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de Havilland 106 Comet

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:D As a number of people have asked me about the Comet following the Mosquito strand, here is the first part of its story:

At 3:10 p.m. on 2 May 1952 a de Havilland Comet 1 airliner of British Overseas Airways Corporation (BOAC) inaugurated the Worlds first fare-paying jet passenger service - less than a decade after the concept of a gas turbine airliner had first been visualised during the Second World War.

The Brabazon Challenge

In December 1942 the first of two 'Brabazon Committees' began their work to evaluate and advise on what types of aircraft Britain would need for civil transport after the war. The Committee was headed by Lord Brabazon of Tara and also included a fellow British aviation pioneer, sixty year old Sir Geoffrey de Havilland.

Inspired by the Wright brothers, de Havilland had built his own aeroplane in 1908-9, and was employed as an aircraft designer at the Royal Aircraft Factory, Farnborough. During World War I he both designed and flew British military aircraft before founding his own De Havilland Aircraft Company in 1920. Building on the great success of the lightweight Moth and Tiger Moth biplanes he turned his attention to airliners - such as the beautiful wooden D H Albatross in the 1930s. His DH 88 twin-engine racing monoplanes of the period had also given rise to the wooden Mosquito - introduced to RAF service in September 1941 as fighter, bomber and reconnaissance type. It was finish the War as one of the fastest of all Allied aircraft - rivaled only by the first of the new jet fighters.

Indeed, the Committee were fully aware of gas turbine propulsion among many wartime and pre-war aviation developments. Despite its early limitations in performance and reliability the jet engine seemed the only realistic alternative to piston engines driving propellers. Supercharging had been used in piston engines for many years but it was clear that their inherent respiratory problems at higher altitudes were marking the limit of their design capability and operational envelope. However the technical adviser to the Committee, then Dr. Harold Roxbee-Cox, later Lord Kings Norton, thought that 'propeller-turbines' would always be more efficient than pure jets, even on long routes. Like pure jets, "turbo-props" would perform efficiently at high altitudes above the turbulent weather that was the lot of even the best contemporary piston engined machines.

More immediately though, American progress in all-metal stressed-skinned design techniques - linked to an enormous building capacity - had already created the ability of the United States to efficiently mass-produce military transports on a scale unimaginable in Europe. It was also clear that when the war ended US production of military aircraft would give way to civilian transports. Indeed, the classic piston powered Lockheed Constellation airliner - with wings based on the P-38 Lightning fighter - was to begin life as a military transport. Britain, of necessity, had been forced to concentrate on the production of fighters and bombers for the immediate needs of the RAF.

Given this situation The Brabazon Committee submitted - in February 1943 - recommendations to the British Government for the development of five specific 'Types': designs solutions with the objective of meeting all perceived post war civilian needs. In addition, the Committee proposed as a stop-gap measure, that wartime bomber designs were to be converted for civilian operations.

The immediate post-war years in fact saw the Vickers Wellington bomber developed into the Viking. From the Avro Lancaster came the Lancastrian and York, and from the Halifax the Halton. Unfortunately these aeroplanes were as crude uncomfortable, noisy and slow as their wartime ancestors - a poor second even to the DC3 - a pre-War airliner which had carried so many men and munitions in the Allied cause. In marked contrast to the Boeing Stratocruiser - which had evolved from the B-29 Superfortress - offered pressurised double decks and a bar! Before then, however, the reccomendations of the Committee were generally accepted by the Government. Work on detailed draft specifications began.

Division of work

The Brabazon Committee continued to meet between August 1943 and November 1945 and various Types soon became closely associated with different aircraft manufacturers. Bristol, for example, opted to build the ill-fated Type III a large turboprop long-range airliner -later to be named the Brabazon. Bristol also opted for the smaller Type Va - which became the successful Britannia.

Vickers chose a medium range turboprop - the very successful Viscount - while Avro was to build the ultimately less successful Tudor. de Havilland had their eye on the Type Vb - which became the legendary Dove - and also the challenging Type IV - defined as a 'jet propelled mail-plane for the North Atlantic'. Initially the objective of Type IV was to carry a ton of cargo at a cruising speed of 400 mph. (644 Km/h) or better. Politically and financially, such an advanced aeroplane would bring enormous prestige to a nation wearied by the effort of war.

Early de Havilland jet projects

The Brabazon Committee was concerned that transatlantic capability did not seem realistic with the current thirsty, inefficient state of contemporary jet engines. But de Havilland had more confidence and the Air Ministry too saw enormous prestige in a successfully developed Type IV. A revised Type IV specification was thus laid down in 1944 - featuring two or more jet engines, the capacity to carry 14 plus passengers over a range of 700 to 800 miles (1127-1287 Km) at a cruising altitude of 30,000ft, with a cruising speed of 450 mph.(724 Km/h). This aeroplane was to be used on the overland Empire routes - where the potential for stop-overs and re-fuelling existed - while experience was gained for the development of a larger, probably re-engined, version for the prestigious North Atlantic run.

BOAC also discussed the Type IV proposal with the Brabazon Committee and the Ministry of Aviation, indicating that it would probably require about twenty-five aeroplanes. This represented an enormous gamble on the part of the airline because the Ministry of Aviation's Procurement Division, with its specification 20/44, had only loosely outlined the design parameters for the project. But BOAC's clear and confident trust that there would a demand for the final product encouraged de Havilland to begin detail design studies.

The Hatfield based firm were committed to powering the Brabazon Committee Type IV, now designated DH 106, with a prime mover designed 'in house' by their own engine genius Frank Halford. His 1941 vintage H.1 turbojet, later to be known as the Goblin, was built by the de Havilland Engine Division and had already featured in a design study of a twin gas turbine version of the Mosquito fighter/bomber.

This work eventually evolved into the D H 100 single-engine twin-boom Vampire fighter, first flown in 1943. And, folk-lore has it, de Havilland's C.C. Walker told BOAC's Campbell-Orde that the airline could have Vampire performance, and a cruising speed 530 mph., in a civilian transport aeroplane if it was powered by turbojets. This 'vision' sold the concept to the Chairman.

By 1941 a twin Goblin engined medium range transport called the D H 95 Flamingo had been under consideration. This would have been a unique de Havilland product, both as a jet passenger aircraft, and as the first all metal stressed skin type assembled at Hatfield. However it was never destined to receive jet propulsion. Yet another design study involved a larger four-engine version of the Vampire, which R E Bishop - Chief de Havilland Designer - described as a "stupid aeroplane".

The obvious choice of engine for the DH 106 was the Ghost - a development of Goblin - which had a first run on the test bed on 2nd September 1945 and later powered the Venom, a twin-boom development of the Vampire.

The main design team under Bishop working on the DH 106 included Chief of Aerodynamics Richard Clarkson and his assistant was David Newman. However, many different design concepts were to pass across their desks before the 106 design was finalised in 1946.

Sweeping changes

Indeed, after initial Goblin and Ghost powered variations were considered, the design of the DH 106 was to change radically with revelations of captured German aerodynamic, jet and rocket technology. Of great interest to de Havilland designers was the use of swept wing configurations in high-speed flight. After all, just as the Hertfordshire based company had built the fastest bomber of World War II so Messerschmidt had built the fastest fighters - the jet powered swept wing Me 262 Schwalbe (Swallow) and the tail-less rocket propelled Me 163 Komet.

Bishop made a fact-finding visit to Germany in late 1945 and - perhaps influenced by what he saw - made a radical new proposal for the DH 106 in May 1946. Configured as a 24-passenger airframe and featuring sharply swept back wings it would also dispense with rear horizontal controls! Power would be from four 5000lb thrust Halford designed engines located in pairs either side of, and next to, the fuselage and buried in the wing root. In this respect, Bishop's new design owed more to the "flying wing" fighters of the German Horten brothers than Willy Messerschmidt's 262. The latter's Jumo engines were mounted in pods under each wing for three practical reasons. The new and unpredictable gas turbines were kept away from the rest of the fuselage in case of explosion or other powerplant malfunction, the jet efflux was similarly kept away from the fuselage and podded engines were easier to maintain.

From an operational perspective, Bishop's new tail-less design could offer an all metal pressurised fuselage some 8ft in diameter designed to take eight rows of seats arranged three abreast. It was anticipated that this version would operate on Empire routes where a maximum stage range of 2200 miles would not be an embarrassment. A reduction in payload (to 18 passengers) would give North Atlantic capability - but only with a stop-over en-route.

Pushing the envelope

The Ministry of Aviation accepted that such a radical configuration required detailed evaluation and so commissioned the building of the D H 108 development aircraft in August 1945. Unofficially named Swallow, the DH 108 was based on the wooden Vampire fuselage with metal wings swept back at an angle of 40 degrees and a fin and rudder topping the engine nacelle. Two prototypes were ordered, one - Goblin 2 powered TG 283 - to test low speed flight characteristics and another - TG 306 with first a Goblin 3 and later Goblin 4 (3750 lb. thrust) turbine - was destined for high speed trials.

During practice for an attempt on the World air speed record - set at 616 mph by a Gloster Meteor IV on 7 September 1946 - TG 306 achieved 637 mph at 9000 ft. Tragically though - on 26 September 1946 - it broke up killing Test Pilot Geoffrey de Havilland Jnr.

A third prototype - VW 120 - was strengthened and made more aerodynamic. This finally set a new record of 605.23 mph over a 100km closed circuit on 12 April 1948 in the hands of a de Havilland test pilot John Derry. Derry also piloted VW 120 when, in a dive, it became the first British plane to exceed the speed of sound. This event came after the American air launched rocket powered Bell X1 had broken the sound barrier for the first time on 14 October 1947.

Sadly all three 108s were destined to crash with fatal consequences, although a less well known but equally import research endeavour was British European Airway's Gust Research Programme of 1946. This involved two civilian registered de Havilland Mosquitos and investigated the jet streams and other upper atmosphere phenomena that the new pressurised gas turbine aircraft would soon encounter.

Lessons learned

By now the technical risks inherent in tail-less designs, and the apparent cost and weight penalties involved, were beginning to be appreciated. Experience with the 108 confirmed fears that this configuration was not yet viable. Back at the drawing board a swept-back conventional tailplane was added to the design, and this - revised - version was outlined when the first Public Relations brochure for the DH 106 was published in May 1946.

Finally, in July 1946, the design team announced a change to the angle of wing sweep. By opting for a 20° sweep - instead of the original 40° - over a ton of weight in wing structure was saved. The change significantly improved handling characteristics - particularly at takeoff and slow speed . Cruising speed was however down from a projected 535 mph to 505 mph. As development continued the length of the fuselage was increased to accommodate 32 passengers seated four abreast in a fuselage of diameter 9ft 9 inches. Gross weight was now projected to be around 100,000 lb

Problems and solutions

In September 1946 the Ministry of Supply (formerly Ministry of Aviation) placed an order for two prototypes to specification 22/46. A price of £ 250,000 for these was set by de Havilland before the final design was fixed. Clearly there was to be no profit with the first batch.

As months slipped by, increased production costs and all-up-weight problems began to dog the design team. It was proposed that a large, single wheel design of undercarriage be adopted early on so that there would be the minimum of delay in getting the prototype airborne - it was never intended for production. Development was well underway of a new type of four-wheel bogie and, it was hoped, it would be available by the time production aircraft were under construction.

Drag calculations also indicated that the design was now 18 percent above specification. So critical did performance calculations become that it was decided to compensate for a possible 'over-shoot' in all-up-weight targets by making provision for rocket assistance on takeoff! The design was modified to incorporate a DH Sprite 5,000lb thrust rocket engine - located between the two Ghost jet pipes on each side of the fuselage. Also evaluated was ammonia injection to boost the Ghost's power. Even in-flight

refuelling was considered!

At 53 inches diameter, Halford's original military version of the Ghost turbojet also created difficulties for the design team too. A slimmer, more powerful, alternative engine (the axial-flow AJ65 - later known as the Avon) was due to be available from Rolls-Royce in the early 1950s (and promised to BOAC for later batches of production DH 106) , but de Havilland decided to "civilianise" its Ghost and avoid delay, although sixty percent of the detail design drawings had to be re-drawn. Development of the "civilian" Ghost was undertaken using two modified Lancastrian aircraft for low altitude evaluation. For this purpose, the two outer Rolls-Royce Merlin engines of VM703 and VM749 were replaced by Ghosts. For high altitude work a Vampire -TG278 - was modified. Finally in June 1948 the Ghost - rated at up to 5000lbs static thrust - received type approval as a civilian power unit.

Further systems and equipment tests were conducted using Vampires, Lancastrians and various other aeroplanes. The shape of the nose, for example, was finalised by modifying a Horsa glider. This strange looking craft was towed behind a Halifax bomber during evaluations!

Further progress came in January 1947 when the Ministry of Supply placed an Intention to Proceed with de Havilland for the construction of eight aeroplanes - all intended for BOAC. Later six more aircraft were ordered for use by British South American Airways thus making a total of 14 orders. However BOAC merged with BSAA. and the total order was revised to nine aircraft. The price per aircraft was still set at £250,000 each and against this figure costs were rapidly rising. The first eight production aircraft were purchased by BOAC before they had even been built with the proviso that they should enter service in May 1952. In December 1947 the DH 106 was christened the 'Comet'.

Comets under pressure

On 23 March 1948 a new World altitude record was set at 59 446 feet over Hatfield by Group Captain John Cunningham flying a de Havilland Vampire specially modified with the perspex bubble canopy replaced by metal alternative. 12 July 1948 also saw the start of the first Atlantic crossing by jet aircraft when six Vampires of 54 Squadron RAF flew from Stornoway via Iceland and Greenland to Goose Bay, Labrador.

The Comet meanwhile was designed to operate at up to 40,000ft for relatively long periods in an environment that was little understood at the time. Designers had to create a structure that was robust enough to withstand high internal and external pressures and sustain very low temperatures - parameters that in many respects could only be guessed at. On military aircraft limited pressurisation had already been used. Now the intention was to pressurise the whole crew / passenger environment at 8.25 psi. : twice the pressure used on other airliners of the time.

A de Havilland innovation - subsequently to become standard practice on all passenger turbojets - was to use compressed air taken directly off the engine's compressors for cabin pressurisation but for a while this practice caused problems with engine over-heating. The Engine Division were constantly under 'pressure' themselves to improve the Ghost's specific fuel economy and 'bleeding off' of hot compressed air did not help matters. Eventually compressed air destined for the cabin was directed via coolers, pressure regulators and humidifiers. More 'bled' hot compressed air was used for de-icing purposes.

The Comet was to be the first aircraft in which the pressure loads were higher than the flight loads. In simple terms previous aircraft had pressure cabins that were much stronger than necessary in order to withstand the flight loads and they had not, therefore, been exposed to the phenomena of 'pressure fatigue' in the same way. This was to be of major significance later on in the Comets history when failures of the pressure cabin were to occur.

Recognising that the company was moving into unknown territory with the unique Comet, de Havilland devised special testing facilities specifically for it. At Hatfield a test chamber was specially constructed, designed to operate at up to an equivalent of 70,000 ft and down to a temperature of -70 degrees centigrade - and allow a considerable margin of safety with respect to both. Whole sections of the pressure cabin structure along with the windows were tested. Test windows were subjected to pressure loads of 8.25 psi. 2000 times and then, for good measure, tested at 100 psi. A forward section of the fuselage was subjected to 16,000 cycles in the water-tank.

The Royal Aircraft Establishment (RAE) at Farnborough had also been conducting extensive tests to investigate the fatigue-life of aircraft structures. Much work had been done on devising methods of measuring various types of loading, for example, gust loading. The RAE had devised an instrument that could automatically count the number of 'accelerations' in an upper atmosphere gust and grade them for severity.

RAE research had led them to believe that continuously repeated testing of the main components and such things as spar joints - if applied to at least six examples - would give very accurate data. The procedure was to apply a constant load and upon that superimpose a heavy and continuous reciprocating load thus simulating positive and negative 'g'. One minute in the test rig was equivalent to one hour of flight. By extrapolating results it was thought the fatigue life of any structure could be accurately determined.

The RAE would test full-scale specimens - such as wings -to destruction on a strength-testing rig. Loads were applied by hydraulic rams. In the case of the Comet the wing and a section of the fuselage were first tested through a certain life-span and then the same specimen was loaded to destruction-point in the strength test rig! There was also a 'cold-box' to simulate temperatures at high altitude and another form of testing was to make the structure vibrate at its natural frequency.

The RAE were consulted early on in Comet development. The first prototype G-5-1 ended up at Farnborough in early 1953 for further testing. By then it had been 'flown' the equivalent of 10,000 hours during de Havilland test flying and structural testing. It was noted though, even after this punishment, that there were few minor deteriorations. The main structure continued to creak and groan reliably under this continuous reversal treatment in which loads from 0.7 to 1.3 'g' were being applied.

Despite this however, as late as 14 November 1951 the Ministry of Supply wrote a letter to both BOAC and De Havilland. This advised that in the opinion of the Ministry - due to lack of conclusive fatigue test data - a life of more than 1 000 hours could not be reliably guaranteed for the Comets. This would represent about one year of airline service rather than the ten years that BOAC would need to recoup its investment. In the end the RAE, BOAC and De Havilland agreed a compromise. Full scale stress testing would be completed after the Comet had entered BOAC service.

Other changes Bishop made for the Comet was the extensive use of Redux metal glue for attaching the skin to stringers and doublers. Although used previously on aeroplanes, bonding had never been used as extensively as on the Comet, but this allowed the use of thinner aluminium plate and avoided riveting. Essentially weight was saved and sealing problems did not arise. In fact Redux bonding added greatly to the structural strength of the aircraft.

At the end of 1948, de Havilland also took the gamble of setting up the BOAC Comet 1 production line before the prototype had flown. The prototype then had to fly perfectly if the line was not to be expensively halted for modifications.

Comet rising

First engine test runs of prototype G-5-1 were made on 2 April 1949 with roll out on 25 July after a

complex program of engine tests. This Comet carried the manufacturer's Class B markings but was otherwise unpainted. It later transpired that painting the prototype would have been at the loss of four seats, so critical was the ratio of thrust to weight. Two days later - on 27th July - the Comet made its historic 31 minute maiden flight. de Havilland Chief Test Pilot John Cunningham piloted the shining silver craft with John Wilson as co-pilot and Tony Fairbrother as flight test observer was. Fairbrother was quoted as saying (in Aeroplane Monthly of August 1989) that, "The Comet must have been one of the all-time technical achievements. I don't think it is too much to say that the world changed from the moment its wheels left the ground".

Less than three years was to elapse from the finalisation of the detailed design specification of the Comet to its historic first flight! Exactly one year later - in July 1950 - G-5-2 the second prototype was ready and development flying accelerated rapidly. Early indications were that the Comet met most of its design specifications. It could cruise at 490 mph. (788 Km/h) at 40,000ft (12,200 m) and, with an all-up weight of 105,000 lb. (47,600 Kg), could carry 36 passengers over 2,600 miles (4,180 Km). There was some flexibility too - with a modest range reduction up to 48 passengers could be accommodated.

The first public view of the Comet was at the 1949 Show of the Society of British Aircraft Constructors at Farnborough, Hampshire on 8th September. Described at the time as "The finest show ever held" it also featured the Bristol Brabazon that had made its maiden flight on 4 September - just four days earlier! Other civilian transports on display included the 351 mph Handley Page Hermes V prototype which -powered by four Bristol Theseus turboprops - was the fastest turboprop transport at the show. Slightly smaller was the prototype Vickers Type 630 Viscount, powered by four Rolls-Royce Dart turboprops. In 1950, the Vickers Viscount became the World's first turboprop airliner to enter passenger service.

However, John Wilson recalls that on flying past the Farnborough crowd at 340 knots a loud bang was heard in the cockpit. On inspection after landing, a thin metal panel in the nose was found to have dished in with air pressure. To save the airframe weight relative to engine power, much of the skin of the Comet had been made with 22 gauge metal - not much thicker than paper - rather than the more conventional 14 gauge.

G-5-1, later given the civilian registration G-ALVG, continued test flights concerned with range and fuel consumption assessment. In October 1949 a round trip to Castel Benito, Libya, achieved an average speed of 448 mph while endurance tests also were completed around the British Isles. In February 1950 the first pressurisation flight to 40,000ft was undertaken (with a cabin pressure of 8.25 psi equivalent to an altitude of 8,000 ft.). Trials during the first year went smoothly with very few problems. The results gained were critical to the success of pure-jet transports in general and to Comet sales potential in particular. There were still many people in the industry who thought that pure-jet transports would never be economically viable. In the event the prototype G-5-1 performed superbly and without difficulty met its design specification. However, all-up weight (AUW) issues still prompted investigations of possible rocket assistance on take-off and in-flight refuelling!

Rockets and refuelling

De Havilland Test Pilot Peter Bois, who joined the Company in 1950, recalled a number of experimental 'Sprite' assisted test flights made between May 1951 and May 1952. These tests were carried out on G-ALVG (ex G-5-1) in which two 5,000lb thrust Sprites rocket motors had been installed, one located each side of the fuselage between the jet pipes of the Ghost engines. They gave a 55 second burn and effectively gave an (approximate) 50% increase in the total available thrust. The technique used was to fire them on reaching 'decision speed' and this would have allowed a, quote,

"very worthwhile increase in the Comets maximum AUW in high temperature/altitude conditions."

However, the 'Sprite' option was not adopted for a number of practical reasons. The fuel used in the Sprite was hydrogen peroxide, which initially required a potassium permanganate catalyst to release the hydrogen, which burned in oxygen - which was also released in the catalytic reaction. This was effective but unfortunately dyed everything in sight a delicate shade of violet!

Things improved somewhat when platinum mesh was used as the catalyst instead of permanganate - the drawback was however that platinum was much more expensive. In practice though the specific problems associated with handling peroxide were not significantly greater than those encountered with high-octane fuel. They were however different. An electric spark in the vicinity of permanganate was of no consequence but even a small impurity in the fuel tank could make it explode.

Large quantities of water always had to be on hand to dilute accidental spills and soon it was decided that the expense of bringing Sprites into regular use would be difficult to justify. Factors included the cost of the peroxide, peroxide fuel availability problems, and the fact that ground crews at all prospective Comet destinations would need special training were taken into account. In addition, peroxide fumes rapidly turned the experimental handling crew into platinum blondes and they were greatly relieved when the project was dropped! However before the project was cancelled the public were treated to demonstrations of Sprite rocket assisted takeoffs at the SBAC show at Farnborough in September 1952.

Under the right conditions however the De Havilland Comet was already capable of some impressive speeds under jet power alone. On 18 March 1950 John Cunningham flew G-ALVG from Hatfield to Rome's Ciampino Airport in 2 hours 2 minutes and returned the same afternoon in 2 hours 4 minutes: thus breaking his record made in a Vampire on 4 November 1948. That journey took a slothful 3 hours 50 minutes and 40 seconds and produced an average speed of 323 mph compared to the Comet's 450 mph!

On 14 December 1950 meanwhile John Cunningham and Peter Bois made a ninety-minute flight in G -ALVG to assess the difficulties of flight refuelling. Unfortunately the tanker aircraft was a converted Lincoln which had a cruising speed considerably less than that of the Comet. The jet was also fitted with a dummy probe and the tanker's supply hose was empty. Peter Bois recalls:

"This increased the difficulty of coupling considerably as there was no weight to stabilise the hose. It needed all John's considerable skill to make the connection and neither of us felt we would have enjoyed being paying passengers in the cabin while the struggle was in progress."

As it happened BOAC pilots said that they were not prepared to be responsible for flying their aircraft so close to another as a matter of routine on scheduled services.

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:D Testing times

In the first 11 months of testing 324 flying hours were completed. Tropical trials took place at Eastleigh, Nairobi, in April and May 1950 where the availability of a high altitude runway in high ambient air temperatures was ideal for the testing purposes. In contrast, Khartoum provided higher temperatures but at a lower altitude. No great problems were encountered during any of these trials.

John Cunningham, when asked to recall how he felt about the Comet as a flying machine, is quoted as saying,

"It felt wonderful, right from the start. The smoothness and comfort were absolutely marvellous. It was my pleasure and enjoyment to help put it all together".

Peter Bois recalled that in the course of development very few faults were discovered. The prototype satisfied the requirements of the Air Registration Board - who, it must be added, were also attempting to write their own manuals on 'pure-jets', literally, as they went along. On one occasion though there was a minor difference of opinion between the two parties. Dave Davies (ARB Chief Pilot) was extensively involved with the Comet certification program. Peter Bois described him as, "an exceptional pilot." But on this occasion he requested that the Company modify the fire-warning bell as he considered that it was not loud enough! The DH pilots thought otherwise.

At the next ARB flight the flight engineer was primed to set off the fire-warning bell during takeoff!

The ARB Chief Pilot was comfortably settled at the controls. Peter continues, "everything proceeded normally, until I called "V1" (decision speed) when, as arranged, the fire bell was set off. Amid loud ringing, To his credit Dave took it pretty calmly and called 'Engine Fire - identify engine - fire warning checklist'. He did however look rather relieved when I answered 'Disregard - just checking your hearing aid!' 'You bastard' he replied." The request to make the fire bell louder was dropped!

One incident that could have been more serious occurred after the Comet had long since passed all the flight tests designed to produce flutter. Peter comments,

"On one of these test flights the aircraft was a few knots below its maximum. When flutter started, the instruments became a blur and break-up seemed imminent. John Cunningham, in the left seat, immediately closed the throttles, while I extended the speed brakes. The aircraft seemed to take an age to decelerate and only stopped shaking at 270 Knots." All were shaken.

It was not possible though to tell whether it had been rudder or elevator flutter that had been induced. A series of test flights were undertaken with the aircraft fully instrumented in an attempt to reproduce and identify the source of the problem. Peter explains,

"Mach and altitude were explored, but it only occurred at a particular Centre of Gravity. It was then realized that this C. of G. resulted in there being zero elevator hinge moment, i.e. under this exact condition you could, theoretically, remove the elevator altogether and still be in trim. As a result there was no aerodynamic damping to prevent flutter starting. This led to the conclusion that the existing mass balance, which was not directly connected to the elevator but to the servodyne linkage, was in no way doing the job! How fortunate that the Comet had power controls, which had the effect of limiting the amplitude of flutter. A manual controlled elevator would certainly have broken away and the aircraft lost."

The problem was solved temporarily by the attachment of an external balance weight. The final solution on production aircraft was an arm and weight fitted directly to the elevator torque tube within the tail-cone fairing.

In July 1950 the second prototype G-5-2 with John Cunningham and Peter Buggé made its maiden flight and was delivered - as G-ALZK - on 2nd April 1951 to the BOAC Comet Unit at Hurn Airport for a '500 hour crew training and route proving program'. During this time, in addition to fuel consumption tests, techniques of holding and descents were extensively evaluated.

Twelve long distance proving flights were made to destinations such as Johannesburg, Beirut, Delhi, Djakata and to Singapore. These flights were not only intended to evaluate the Comet on the longer BOAC routes but were also used to ascertain the need for, and facilities available at, a number of re-fuelling points en-route. The Comet required BOAC to re-think its established handling procedures and re-assess the turn-around times before they could attempt to schedule services.

The Comet had little difficulty in satisfying the ARB and being granted it's Certificate of Airworthiness.

Often, in the early days, it was a scramble to get the aircraft into the air for a series of test flights because some component or other was not yet available. The majority of Comet components were manufactured 'in-house' - although some specialist items would be supplied from external sources.

On one occasion during a flight the crew detected the unmistakable smell of hot electrics. A frantic search ensued. After a while smoke began to curl out from below the windscreen pillar - the problem was eventually traced to a faulty wiper motor. It turned out that this particular motor was a 'one-off' having been disabled with a locking pin, because it did not work too well! Someone had accidentally knocked 'on' the switch so the wiper was trying to operate while being prevented from doing so by the pin! The motor had over-loaded!

On another occasion the DH team were performing in-flight re-light tests on the Ghost engines. On one such test some insulation material located between the engine jet-pipes filled with fuel and ignited. Fortunately one of the flight observers saw the flames and alerted the crew. In this case the fire burned itself out - with only minor damage to the surrounding structure. Following this incident there was a rapid redesign of the fuel drainage system so preventing fuel leaking into this critical area.

Standard practice is that when a problem of this nature occurs, the cause is properly identified. Where there are possible safety implications - the Company would routinely notify the Ministry of Supply of the facts so that they could pass on details to other manufacturers. Sadly, not long later, a similar fire broke out on a prototype Vickers Valiant bomber which resulted in its total loss. In the case of the Valiant the fire could not be seen from anywhere onboard and continued to burn unchecked until it caused a major structural failure and a subsequent loss of control.

On one occasion G-5-2, the second prototype, was being tested in a high-speed dive. Suddenly there was a loud bang and then nothing else to indicate a problem - no unusual noises or buffeting. Later it was discovered that a panel measuring some 6ft by 2ft from the top of one of the engines had broken away! The panel was subsequently returned to de Havilland. By a farmer into whose field it had fallen! The cause of this failure was self-evident - a complete line of rivets was missing! Amazingly the aircraft had already flown several hundred hours and at higher speeds than on the day of the panel loss.

The stall characteristics of an aeroplane are extremely important and some controversy about those of the Comet on, or near, the ground - arose after a couple of accidents in later service. However, Peter Bois was quoted as saying

"After relatively little development the Comet had excellent stall characteristics. Of course, the ARB required the stall behaviour to be checked over the whole weight range, at all centres of gravity, power on and power off, gear up, gear down, clean (no flaps), take-off flap, landing flap and at low and high altitudes. In addition to stalls in level flight, accelerated stalls i.e. at various bank angles, had to be done".

The permutations and combinations were endless. de Havilland test pilots liked nothing more than to impress 'visiting' crew who often joined the more 'routine' test flights. They were extremely confident too! A pilot from an American airline had been invited to take the right seat and was clearly impressed by how dark the sky became when the aircraft climbed above 40,000ft. On this particular flight the crew had planned to do some stalls at low weight and aft CG on the descent between 20,000 and 10,000ft.

Unfortunately the weather deteriorated as the aircraft met a frontal system and they entered cloud at 22,000ft. Our visitor was speechless, when I started a series of stalls in different configurations, all on instruments."

Speed for sale.

When Concorde was introduced there were very few military aircraft that could catch it and fewer still could maintain Concorde's speed - but then only for minutes at a time! When Comet was introduced a similar situation arose ! On a demonstration flight for Air Chief Marshal, Sir Ralph Cochrane, the Comet demonstrated this. An interception by Gloster Meteors had been laid on. The Comet was cruising at about 35,000ft when a Meteor managed to pull along side. Peter Bois recalls:

"John Cunningham increased power to maximum thrust and put the nose down a little. The pilot followed but, very soon our speed exceeded the Meteor's critical Mach number and it started to get wing drop. He struggled to hold station for a short time, then had to pull away, shaking his fist in fury."

The pilot of the Meteor was unaware of the identity of the VIP passenger who found the incident highly amusing!

The world's first Certificate of Airworthiness (C of A) for a commercial jet passenger aircraft was granted on the 22nd January 1952. During January simulated passenger operation flights were undertaken to South Africa so that flight deck crew, cabin crews, and the aircraft handlers could familiarise themselves with the Comet.

G-ALYP (known as Yoke Peter) was delivered to BOAC on 8th April 1952. The last of the line G-ALYZ was delivered on 30th September that year. Airlines now began to sit up and take notice of the Comet. Overnight, it seemed, BOAC's rivals had been disadvantaged. They could not compete with slower, less glamorous aeroplanes - the only solution was to offer jet services too.

Carriers were soon converting their options into firm orders - the sales drive had begun. Some airline operators had more foresight than others. In December 1949, following the SBAC show of that year, Canadian Pacific ordered two Comets - in this case opting for an up-rated version - the Comet 1A.

Early on in the Comet program it had been proposed to offer an up-rated version of the Comet. It was to be powered by a development of the Ghost 50 Mk.1 engine. Equipped with four 50.Mk.2s, it had a greater all-up weight and increased full capacity (6,909 Imperial gallons) this version - designated the Series 1A - it was ideal for Canadian Pacific's Vancouver-Hong Kong route. The 1A also attracted other orders - one each from Air France, U.A.T., and two more for the Royal Canadian Air Force. Panair do Brasil joined the queue placing orders for four Comet 2's, which too had just been announced, they also negotiated options for two Comet 3s. Now the problem for de Havilland was one of production capacity. Shorts of Belfast were given work on sub-assemblies and a second assembly line was set up at de Havilland's Chester factory.

At 3:10 p.m. on 2nd May 1952 BOAC, with Yoke Peter, inaugurated the World's first fare-paying jet passenger service from London, Heathrow to Johannesburg via Rome, Beirut, Khartoum, Entebbe and Livingstone and was completed in 23 hrs. 37minutes. After 6,724 miles (10,810 Km) it arrived three minutes ahead of schedule! The crew comprised Captains A. M. Majendie, J. T. A. Marsden and R. C. Alabaster and First Officer Ken Emmott.

Only time and fate however would decide the true legacy of the de Havilland Comet.

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;) The Jet Set

As early as May 1952 the new Comet jetliner received Royal patronage when Queen Elizabeth the Queen Mother and Princess Margaret, along with their hosts Sir Geoffrey and Lady de Havilland, enjoyed a four hour 'leisure' flight round Europe. The following year they used Comet to attend the Rhodes Centenary celebrations at Salisbury, Southern Rhodesia.

Meanwhile mid May 1952 also saw route proving and crew training extended to the Far East. In August 1952 services began to Colombo - the journey taking 21½ hours. Singapore services began in October 1952 and, on 3rd April 1953, a service was opened to Tokyo. The 10,200 miles covered in just over 33 hours. Previously it had taken 86 hours! The Comet 1 operated at an amazing 89 percent of maximum possible load. Generally it cut flying times by fifty percent.

With its superb appearance and performance the Comet became an over-night success with crew and

passengers alike. It attracted the sort of public interest that only Concorde would be able to match twenty years later. It is easy to forget how revolutionary Comet was, and how modern and sleek it appeared compared to its contemporaries. BOAC Comet seats between London and Johannesburg sold out months in advance and celebrities aboard included Frank Sinatra, Trevor Howard, Countess Mountbatten of Burma, Grace Kelly and Clark Gable.

But the Comet had grown: the prototype was bigger and, inevitably, heavier than 1946 targets. Span was now 115ft (35m), length 93ft 1inch (28.37m) and weight - initially increased by some 5000lb (2273Kg) - was to increase by a further 2000lb (909Kg) before introduction into service. To offset this, and improve the seat costs/mile ratio, capacity was increased to 36 - arranged as before. Other Mk.1 vital statistics included a wing area of 2015 sq.ft. and maximum range (with an 8 800 lb maximum payload and allowing for standard airline reserves of fuel) of 2,100 statute miles (3,360Km) Stage length was reduced to 1,830 miles (2,928Km) with a payload of 11,600lb (5273Kg).

With an all-up weight (AUW) of around 105,000 lb. (47,727Kg) a cruising speed of 490 mph at an altitude of 35,000 ft. (10668m) represented marginally less than projected performance. Four Ghost 50 Mk.1 (D.Gt.3) engines, each now offered 5,050 lb.static thrust at 10,250 rpm while later the Mk.4 version of the Ghost 50 provided an equivalent 5,050 lb but at a slightly lower 10,000 rpm. Integral wing tanks held a total of 6050 Imperial Gallons.

Comet 1A

Soon after the Comet 1 was introduction into service the need for greater operational range and higher passenger payloads became readily apparent. Indeed the prospect of future foreign sales would hinge on rapid development of the type. The first result of de Havilland deliberations was the Mk.1A - an evolution of the Comet 1. Designed to carry up to 44 passengers over slightly longer distances (1770 miles) the increased all-up weight (now 115,000lb (52273Kg) was compensated for by the introduction of a slightly more powerful version of the Ghost. The 50 Mk.2 (D.Gt.3) was rated at 5,125 lb thrust at 10,350 rpm and made use of methanol injection. Fuel capacity was increased by the installation of extra centre bag tanks giving an additional capacity of 856 Imperial gallons. Externally the Mk.1 and 1A were little different. Dimensions of the 1A were as for the Comet 1 in length, height, span and wing area. Now 36-44 passengers could be accommodated seated four abreast. Range was estimated at 1770 miles cruising at 490 m.p.h. at 40,000 ft. Total fuel capacity was now 6909 Imperial gallons.

The first two losses

Ten Mk1 Comets were delivered to BOAC between G-ALYP in April and G-ALYZ in September 1952. However, just one month after delivery G-ALYZ - Yoke Zulu - was written off when it failed to get airborne and overshot the runway from Ciampino, Rome. It was raining on the night of 26 October 1952 and during the takeoff run 36 year old Captain Harry Foote concluded that the Ghost engines were lacking thrust and abandoned the takeoff. There were no casualties - but the loss reduced the BOAC fleet to nine.

On 3 March 1953 a very similar "ground stall" afflicted the first Canadian Pacific Airlines (CPA) Mk.1A on its delivery flight while attempting to leave Karachi en route to Sydney. On this occasion all eleven people on board CF-CUN "Empress of Hawaii" - the five strong Canadian crew, five de Havilland technicians and an Australian - were killed

Investigators attributed the cause of both losses to pilot error: specifically to over-rotation [lifting of the nose] during the takeoff. This, it was claimed, resulted in the nose of the aircraft being too high, thus the wing 'angle of attack' was too steep to get sufficient lift. Around the World, however, pilots' professional organisations took up the matter on behalf of the discredited crews. In particular, Captain Foote - according to his widow interviewed on a 2002 British Channel 4 documentary - was forced by BOAC to confess that the accident was his fault to protect the good name of the Comet. Foote was then demoted to the airline's freighter fleet.

The BOAC Training Manual noted that at an increase in wing incidence [angle] to 9° would result in a stalled, or semi-stalled, wing - appreciably affecting acceleration. The official investigation showed that Yoke Zulu, with the tail bumper scraping the ground, would have assumed an incidence of 11°! Therefore, with a takeoff weight of 100,370lb, the aircraft could never have flown!

Findings of the Yoke Zulu Investigation were discussed in Parliament. The British Airline Pilots' Association (BALPA) repeatedly requested the Minister of Transport and Civil Aviation to re-open the inquiry, which had been conducted by its own Accident Investigation Department, because, they said, further information and new evidence had come to light. However the Chief Inspector of Accidents did not think BALPA's evidence relevant. So BALPA quoted the current Comet Training Manual as giving a 15% margin of safety. Translated this meant that 'unstick' could be made at 1.15 times stall speed. But, they argued, this was not reflected in the Company's Operations Manual. In this Manual, for the given weight, 'unstick' speed was given as 112 Knots.

Now the Flight Manual gave the power-off stall speed as 102 Knots - a margin of only 10% - and not consistent with training notes! BALPA also believed that the case of the Canadian Pacific 1A accident revealed a phenomenon new to the study of aerodynamics. When or near the ground the Comet was found to have appreciably higher stalling speeds than in free air. This was proportional to weight - in the circumstances the stall speed would be some 9 Knots higher than previously assumed.

BALPA further pointed out that since the accidents BOAC had twice altered the recommended takeoff technique by increasing the 'unstick' speed by six Knots and more attention was paid to this phenomenon in crew training.

Nowadays - partly thanks to experience with the Comet 1 - takeoff speeds are laid down for all normal conditions and are calculated for each particular takeoff. Ground stalls are thus rare because of the introduction of the concept of 'Rotation Speed'. The pilot does not attempt to lift the nose - rotate - until a certain speed - Vr. This along with the 'decision speed' V1 - and V2 initial climb speed - allow a smooth and safe transition between having all the wheels on the ground, maintaining a speed above the stall, to being airborne at V2.

CF-CUN 'Empress of Hawaii' meanwhile had commenced its takeoff run but before reaching V1, it seemed, the pilot rotated too soon to generate enough lift. The 1A was at the weight limit for the conditions. The crew had planned to leave at night so that the air temperature would be lower but, even so, it was still 8° above ISA (International Standard Atmosphere). Water/ Methanol injection was used to compensate for the Ghost's power loss and there was no wind.

No official report was published into this accident. But a summary was issued later which stated, inter alia,

"at this high weight, strict compliance with the take-off technique would be necessary for a successful take-off".

Again the International Federation of Airline Pilots Associations was concerned about the summary conclusion which amounted to 'pilot error' by Capt. C. H. Pentland. The Association was frustrated in its investigations and felt that not all the relevant evidence had been made available to them. They wanted more information as to the actual stalling speed of the Mk.1A, in the prevailing conditions. Weight, ambient air temperature and humidity were taken into account, particularly in the light of subsequent knowledge as to the adverse influence of 'ground effect' on the stalling speed. They reasoned - it was possible that the Karachi Comet was "scheduled to unstick at one or two knots above or below the stall".

Concerning the accident to Yoke Zulu the International Association again argued: if there had not been a problem with the Comet 1's ground stall characteristics why was there a new paragraph dealing with takeoff in the proposed UK edition of the International Standard of Recommended Practices?

This edition advised that 'no attempt should be made to takeoff until a speed of 1.15 times minimum 'unstick' speed is reached. These 'margins' may be reduced to 1.1 or 1.05, relatively, when the limitation is due to undercarriage geometry, and not to ground stall, characteristics'.

The response of de Havilland was that modifications were necessary to prevent even the inadvertent application of 'over-rotation'. Mock-ups of a modified 'drooping' leading edge - ordered by Chief Designer R E Bishop - gave acceptable results during test flights and only had a marginal detrimental effect on the aircraft's speed. Interestingly prototype G-5-1 had been fitted with leading-edge slats to prevent stalling but, in numerous tail-down takeoffs, they were found to offer little benefit. On the negative side they increased significantly mechanical complexity of the wing and contributed to an additional weight penalty (already problematic) so it was decided to dispense with them. In testing it had been proved that at normal weights and operational temperatures the Comet would take off, tail bumper touching the ground, with no problem. However, a new leading edge design was applied to future Comets as a result.

In fact both 'ground stall' incidents had one factor in common - both occurred when the aircraft was 'heavy' and operating at higher than average temperatures. Normally scraping the tail in no way critically affected takeoff performance. Peter Bois (de Havilland Test Pilot 1950 - 1956 - Comet Development) explained,

"In both these accidents the high weight and temperature were critical. The crew rotated to a point where the wing stalled - thus the drag was so high that the aircraft could not accelerate beyond the stall speed, before running out of concrete".

Indeed de Havilland had demonstrated to Canadian Pacific crews tail-down takeoffs during both day and night training flights - thereby possibly adding to the very accident they were trying to avoid. Peter Bois continues:

"The most probable explanation of this accident was that it was caused by extreme fatigue. The pilots spent the whole day before departure making final arrangements, which they did not complete until about 2 a.m. the next morning. They had, perhaps, three of four hours of sleep before a, circa 8 a.m., departure for Beirut. The flight time was about 5½ hours. The Beirut ground stop lasted some two hours and the flight to Karachi another 5½ hours. A further lengthy ground stop meant that the crew had been active for some 40 hours, with inadequate sleep, before the accident occurred."

The most tragic fact was that the crew almost got away with it. "Score marks on the runway indicated that the tail bumper was touching for a distance of about eight hundred metres. Shortly before the end of the runway, the marks ended. Tracks in the sand, past the runway end, showed the nose wheel in ground contact. Some distance on, the nose-wheel tracks ceased, followed by those of both main landing gear. Clearly, the aircraft became airborne for a short time before striking a low stone wall bordering a deep gully, into which it plunged and exploded."

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:huh: Dakar and Calcutta

The Comet had an excellent safety record and was much respected by the industry as a whole. But such was the importance of the Comet that even minor 'incidents' became particularly significant. However, in those pioneering years of jet passenger flight, all such events had a major influence, one way or another, on aircraft design, construction, operation or on safety; on public opinion or, in a general sense, on industry practice world-wide. One example of this - allied to the need to look again at the stall characteristics of the wing leading edge - was criticism about the power assisted controls which were said to lack feel. In general the systems simplicity and lightness outweighed any risk of over-control but de Havilland continued to work on this with the resultant introduction of 'Q feel' - first seen on the development Mk.3. As the name suggests, the controls, although still fully powered, had been given an artificial degree of feel and were much more pleasant to use.

On 25th June 1953 another Mk.1A was written off at Dakar, Senegal when F-BGSC, belonging to Union Aéromaritime de Transport (UAT), skidded off the runway. No one was hurt but the aircraft, which only been in service for just over seven weeks, was an insurance write-off! Much more mysteriously though, on 2nd May another BOAC Comet 1 - G-ALYV, Yoke Victor - broke up in a violent tropical storm near Calcutta. 37 passengers and a crew of six were lost - commanded by Capt. Maurice William Haddon - one of BOAC's original Comet Captains and a very experienced pilot.

Newspaper headlines ran 'Airliner knocked down by tempest'. There had been reports of extreme turbulence at approximately 10,000 ft in cumulous-nimbus clouds. Opinion was that the storm would have downed any aircraft. The last contact with the aeroplane was 6 minutes into the flight when the pilot routinely reported that he was climbing. The aircraft would have been at approximately 10,000ft.

Comets had by now flown over a 100 million revenue passenger miles and had carried 28,000 passengers, but there was much concern because of the apparent suddenness of the accident. A special meeting was convened in London with senior executives headed by the BOAC Chairman Sir Miles Thomas. After a careful review of reports they decided that, for the time being, scheduled Comet services would continue. British crash investigators assisted an Indian Investigation team. T. R. Nelson was Senior Inspector of Accidents, Ministry of Civil Aviation Accident Investigation Branch and J. B. Folliott was BOAC's Chief Investigating officer. The British authorities came to the conclusion that the loss of the aeroplane was directly or indirectly due to the severe turbulence. However the Indian Court of Inquiry decided the 'probable' cause of the loss was due to:

"severe gusts encountered in the thunder-squall, or over-controlling or loss of control by the pilot when flying through the thunderstorm."

Either way, the results of the Inquiry were unsatisfactory. BOAC and de Havilland issued a combined statement which made it clear that they did not agree that over-control or loss of control was the likely cause. They concluded that the Indian findings were theoretical and were not based on a detailed examination of the wreckage. Perhaps the true reason for the loss of Yoke Victor will never be established. Very little wreckage was recovered as it was distributed over a wide area. Could a structural failure have occurred ?

Peter Bois, a de Havilland Test Pilot during those years, proposed one personal theory to account for the loss of control and subsequent break-up of the aircraft. Explaining that the Captain of Yoke Victor was extremely experienced and highly respected by his colleagues, the investigators considered it impossible that he would have taken the aircraft into extreme turbulence at speeds higher than those recommended. Conversely, could he have taken the aircraft into the turbulence at too low a speed? It was possible. He may have concluded that such a manoeuvre may be the safer option. Certainly he may not have realised that it was perhaps far more dangerous to fly into severe turbulence at below the recommended rough-air speed. He was not after all a test pilot.

Peter Bois described the strange sensation that can be experienced. Reducing speed,

"can easily lead to a low speed stall. The stall is followed by the aircraft pitching nose down and accelerating very rapidly to a speed vastly beyond the aircraft's structural limit."

Peter explained that unless one has experienced it oneself it is very difficult to appreciated the degree of, "lateral upset" which can be induced. On one later occasion, a very sturdily built Douglas DC8, encountered extreme clear-air turbulence which resulted in the aircraft being thrown into a sixty degree bank, "against full opposite aileron." The flight recorder registered structural stresses close to structural limits - the crew thought they were going to lose control at one point!

"this took place under visual flight conditions, in daylight. The Comet accident took place at night and in cloud, so it seems possible that the aircraft became inverted. There was also some evidence in the wreckage, consistent with this idea."

Yoke Peter

Then disaster struck again. On January 10th 1954 G-ALYP - commanded by Capt. Alan Gibson with Capt. Livingstone (BEA) and Capt. V. Wolfson (BOAC General Manager subsidiary companies) and 29 passengers - including the famous War Correspondent Chester Wilmot - crashed into the sea south of Elba shortly after taking off from Rome. It was during the climbing phase and this factor led to much speculation that the accident could be linked in some way to the fate of Yoke Victor in Calcutta. 20 minutes after takeoff, Capt. Alan Gibson had a conversation with a colleague in an propeller driven Argonaut departing Ciampino Airport, Rome. The Comet had cleared 26,000ft, no problems were reported and there was no record of severe turbulence. Although there was no clue as to the possible cause, as a precaution, BOAC suspended all Comet services.

Sabotage was considered - witnesses reported hearing explosions. Others concentrated on more practical possibilities such as an explosion of a kerosene-air mixture - possibly somewhere in the wing structure - or an explosion of vaporised hydraulic fluid. Both kerosene/air mixtures and hydraulic fluid vapour concentrations were known to be explosive in certain circumstances. But this was pure speculation.

With the Corporation's entire Comet fleet grounded, a though examination of the remaining Comets began. The feeling began to grow that the problem could be more fundamental - something not previously considered. But by routine examination it was unlikely that incipient structural failure, if the was the cause, would be detected. All this attracted wide publicity. It reassured the public that the authorities were determined to discover the cause. Air France and UAT gave their Comets similar examinations. The Canadian Air Force, in contrast - not being subject to civilian constraints - did not follow the lead.

The Comet was not after all the first new civil aircraft to suffer mysterious failures early on in its service life. The DC6 suffered two accidents (one with fatalities) after mysterious fires broke out. These were eventually traced to a fuel immersion pump which, when accidentally left on, caused excessive pressure and fuel to vent into the airflow and onto a combustion heater. For a long time the actual cause evaded the investigators.

The withdrawal of the Comet from service resulted in great difficulties for BOAC. If suspension was temporary, other aircraft could be drafted in to cover the vacant routes. If, however, matters were to drag on indefinitely the Corporation would have a major problem on its hands.

With no indications as to the cause extensive testing of the remaining Comets was stepped up, undertaken by de Havilland, BOAC and the RAE. The Engineering Divisions inspected all aircraft for structural problems - particular attention being paid to those aircraft having flown the greatest number of hours. The Royal Aircraft Establishment also conducted specific tests on a prototype airframe. In addition BOAC were studying component failure in one aeroplane and electrical, hydraulic or control systems failure on another example.

Everybody was under pressure to do something. De Havilland had to restore confidence in the Comet. BOAC had to get the Comet back into service. Politicians and the public alike needed an explanation for the losses. In the meantime a number of precautionary modifications were adopted for the Mk.1. Armour plated shields were placed between the fuel tanks and the turbine blades - the fear was that a hot turbine blade could shear and rupture the fuel tank. Modifications were made to allow the battery area to be vented so as to prevent the accumulation of hydrogen gas. Additional fire warning detectors were to be installed in the engine cells. Special metal-braided fuel hoses were used with more frequent routine inspection of them. Other changes included better engine breathers, another temperature gauge provided in the equipment bay and additional ducting of cool air to electric motors to prevent overheating. There was also the re-siting of hydraulic drain points and a new relay was provided for the battery change-over. There were improvements too in the ventilation to the rear fuselage under-floor area, and extra smoke detectors were installed at the rear. There was also a reduction of the fin spark gap (designed to discharge static electricity more readily). Also the removal of the rudder trailing-edge strip, provision of drain holes in the rear-spar centre section inspection door, and the reinforcing of the wiring to the ADF aerial amplifier in the aileron booster bay. Another modification was the fitting of larger clips on the booster pump circuits.

Most of these modifications were destined for later models anyway, many having been devised as a direct result of operational experience. Once the decision to ground Comet had been taken the opportunity was taken to 'update' the aeroplane as much as possible. Hopes were high - few aircraft had been more thoroughly and realistically tested than Comet.

Meanwhile initial attempts to locate the wreckage had failed. The Navy was asked to assist. The Commander in Chief, Mediterranean - Admiral the Earl of Mountbatten of Burma - coordinated a Royal Navy task force. HMS. 'Wrangler' and 'Sursay' were joined by the salvage vessel 'Sea Salvor' and the boom defense ship 'Barhill' . Now specialist equipment was available in the form of under-water television, special diving suits, a diving chamber and heavy lifting gear. By early April an amazing 65% of the Comet had been recovered.

On March 12 1954 - after extensive modifications - BOAC G-ALYW made a test flight with ARB and Ministry of Civil Aviation engineers. This was necessary prior to the re-introduction of scheduled services. No-one could think of anything else that could be usefully done to increase the safety of the aeroplane and while out of service the aircraft was not producing any return for the heavy financial investment committed to it. So it was on 23 March 1954 that the decision was taken by the Corporation - with the approval of the Minister, the ARB and the Air Safety Board - to resume jet services.

Yoke Yoke

Seventeen days later, 8th April 1954 BOAC announced that it had ordered the grounding of all Comet airliners throughout the world. This decision followed the news that Yoke Yoke, carrying fourteen passengers and a South African crew of seven, was missing. After leaving Rome the crew had signalled that they were "over Naples and still climbing". Nothing more was heard. At the crash site in the Tyrrhenian Sea, north of Stromboli (NNW of Messina, Sicily) five bodies and some wreckage was recovered early on. The depth of water in this region was estimated to be around 500 fathoms - far deeper than Yoke Peter's Elba crash site.

Comets grounded

Certificates of Airworthiness withdrawn and all Comet operations were suspended. Special crews were dispatched to ferry Comets home from wherever they were when the order to cease operations was received. No fare-paying passengers were carried aboard these aircraft. The only exception was the development of the new Comet 3 which continued its test flying programme. The Royal Aircraft Establishment began a major investigation under the direction of Sir Arnold Hall. Sir Miles Thomas of BOAC summed up feelings when he said,

"we have got to do some fundamental thinking about the Comet altogether."

In April 1954 John Profumo, Joint Parliamentary Secretary to the Ministry, made a statement to Parliament announced that a public inquiry would be held into both Comet accidents. The Ministry of Supply would arrange and co-ordinate an exhaustive investigation into, and tests upon, the aircraft. The full resources of his department would be put at the disposal of the investigators. The RAE, Boscombe Down and de Havilland would be heavily involved. Lord Selkirk said,

"It should be recognized that this is not a time for despair, but rather a challenge to the whole engineering and scientific ability of this country."

Looking for clues

A major investigation was set up and a Court of Inquiry sat to consider all the evidence. Apart from specific examinations of those aircraft having accumulated as many hours as the two lost Comets, three lines of investigation were pursued: one of the returned Comets was stripped down and used for extensive structural testing, another underwent special test flights with RAE and de Havilland crews. This aircraft was loaded with strain-gauges and huge amounts of data was obtained for further analysis. Lastly, despite the problems associated with the depth of water at the Yoke Peter crash site, it was hoped that enough wreckage could be recovered to enable the investigation team to pin-point the cause

of the disaster.

All Comets were recalled for investigation and tests. At BOAC maintenance work was concentrated on two aircraft - one with 3510hrs and the other 3471hrs which made them of particular interest since Yoke Peter had 3605 hrs at the time of the crash. All stripped out parts were set aside, labelled, and meticulously examined. The engines were removed for separate examination. The frame of the Comet was further stripped of sound-proofing and trim to expose the structure both inside and out. Another aircraft had its electrical systems examined in detail.

de Havilland were hard at work too. G-ALYU returned to Hatfield in April 1954 for detailed examination. It too had flown over 3,500 hours so it was of particular interest. At Hatfield the fuselage was modified for under-water pressure testing. However the actual testing was performed at Farnborough where, after the wings had been refitted, the structure was subjected to pressure testing at the same time as wing loading cycles were being applied

So to sum up the other British Comets were distributed thus:

G-ALVG was at RAE Farnborough undergoing structural fatigue and proof loading tests

G-ALYS was undergoing a more general detailed examination at Farnborough.

G-ALYX was flown back from Cairo to Hatfield for fuel seepage testing using specially dyed fuel.

G-ALZK the second prototype aircraft (G-5-2)

G-ALYT had been fitted with Avon 501 engines for Mk.2 development.

G-ALYW was flown from Colombo to London Airport in April before transfer to Hatfield.

G-ALYP (lost at Elba),

G-ALYV (lost at Calcutta)

G-ALYY (lost at Stromboli)

G-ALYZ (lost at Rome)

G-ALYR was severely damaged when it ran off a perimeter track while taxiing for take-off. Repaired and ferried back to London Airport it was unlikely to go back into service after structural testing

BOAC had bought the second Canadian Pacific Comet (CF-CUM) and re-registered it G-ANAV. This aircraft had strain gauges installed at London Airport and was then transferred to Farnborough for flight-testing. de Havilland and RAF crews undertook these flights. Leading the flight test team was Sqd. Leader Roger Topp (later famed for his 'Arrow Nine' formation when he commanded the RAF aerobatics team). de Havilland Test pilots accompanied these flights as advisers, for example, as to whether a particular manoeuvre had been performed by the Company or whether they were operating in 'unknown territory'! Peter Bois accumulated some eighty hours with this team and described them as skilful and highly professional, "a pleasure to fly with."

The flights could be extremely hazardous! One unexpected problem that could be encountered was from the 'bends'. Test aircraft operated un-pressurized - so for most of the flight oxygen was necessary. Some crew members were more susceptible to the bends than others - it was unpredictable and could be related to a particular flight. Because of this phenomena all the crew members were tested in a decompression chamber - the sort of chamber used by divers. When suffering from the 'bends' aircrews could experience varying degrees of discomfort, ranging from mild to excruciating pain.

On one occasion a replacement de Havilland Flight Engineer, who had successfully passed the decompression tests, joined the test flight. Take-off was at 4:20 am to allow four hours of flight before the sun could affect fuel cooling -the object of the test. They climbed to 34,000ft and then a low speed cruise was started. After 20 minutes the F/E was taken ill and clearly was in great pain. He gallantly elected to continue with the flight but he was over-ruled and the flight abandoned. This engineer was to fly at even greater altitudes without mishap.

G-ANAV had been fitted with strain gauges at various critical points on the aircraft. Loads were measured during turns, pull-ups and pushovers at various speeds and at various altitudes. de Havilland had already performed many of these tests themselves. Peter describes a typical test flight with RAE personnel,

"A number of flights were made through cloud, to check the stresses during turbulence. At the several flight observer stations positioned in the cabin section, instrumentation allowed the stress figures to be observed in real time as well as recorded. A Dr. Burns directed this programme from one of these stations. Brilliantly clever, this lady was equally decorative, but she possessed far more courage than was comfortable!"

After several passes through turbulent cloud, increasing speed each time, Dr. Burns had registered what she regarded as some interesting readings but they were not 'very high'. She requested that the manoeuvre be performed at some 30 knots faster! The crew dissented having registered some very high readings on the cockpit accelerometer during that previous run! Dr. Burns, scathingly, "Well, if you don't like it, make it twenty knots, but thirty would give a worth while figure!"

"Much as I admired her, she scared the hell out of me!"

The RAE tests also required evaluation of the accelerated stall. In these the Comet was exceptionally well behaved. When stalled in a 45° turn the Comet's nose would drop and the aircraft gently roll to some 30-35° in the other direction, before the ailerons became effective. Successive flights were undertaken at increasing bank angles. The RAE wanted to determine whether the Comet had a tendency, as was the case with some other aircraft, to roll to an inverted position in stall recovery. Even with 80° of turn at the stall the opposite roll in recovery, could be stopped at about 65°. Some aeroplane!

There was much speculation as to the cause of the last two fatal Comet losses. For example, it was suggested that some form of catastrophic engine failure may have been to blame for the loss. It was argued that in each case the Comets were climbing on full power. Yet this had not been borne out in tests ... the Ghost had been spun to some 17,000 rpm without failure...whereas in the takeoff phase only 10,250 rpm would normally be required - and of course the engines would be throttled back once airborne. In any case there was no evidence of engine failure in wreckage from the Calcutta or Naples sites. It will be recalled that one of the modifications made before Comet services resumed in March 1954 had been the fitting of amour plated shields between the engines and the fuel tanks on all Comets. It was extremely unlikely that turbine failure could have been the cause. Another possibility was an explosion - perhaps in a nearly empty belly tank, which could, under certain conditions of temperature and pressure, explode. Was there a possibility of a spark igniting the vapour given off from the hydraulic fluid - which is not flammable under normal conditions - but may be so under exceptional conditions? Both phenomena were known. The ability of hydraulic fluid to ignite was demonstrated by an incident that occurred during the testing programme. On this occasion Peter Bois had been involved in a series of acceleration/stop tests. The disc (the Comet was the first aircraft to have disc brakes) became so hot that when leaking hydraulic fluid was accidentally sprayed on to it caught fire.

"In the cockpit, we noticed nothing, braking was completely effective and it was only the arrival of a rapidly dispatched fire wagon and a call from the Tower that stopped us from continuing the tests." The Comet was also the first civil aircraft to be pressure re-fuelled. Could this have been the problem - at a rate of 300 gallons a minute could the aircraft be accidentally overloaded? It was believed that this was exactly what happened to an RCAF 1A on a training flight.

Some pilots speculated that with fully powered flight control systems a lack of feel could result in the pilot not being able to sense the excessive loading on the airframe (from excessive stress for example) and, by over correction exacerbate the problem?

In the early part of the investigations, failure of the pressure cabin was not considered a strong possibility. It was recognised that if there had been a sudden decompression - and the passengers had blacked out - the pilots were provided with there own oxygen masks that were triggered automatically on decompression. They at least should have been OK. In fact there had been many reported examples of sudden decompression at 20,000ft - particularly after windows or astrodomes had failed in flight - and usually a safe landing had been made. However none of the Comets had been at cruising altitude when disaster struck.

One step back

In early May production of the Avon powered Mk.2 Comet - first flown on 27 August 53 - was suspended, as was work on the prototype Mk.3. All the modifications appeared not to be been sufficient to prevent further losses. So the Company had no choice but to await the findings of the official investigations and the conclusion of the Inquiry. Meanwhile BOAC found themselves acutely short of aeroplanes. They were forced to suffer the embarrassment of having to negotiate with rival carriers in order to offer their passengers seats.

Piston aircraft were urgently needed to provide carrying capacity pending the arrival of the Britannia. Discussions took place with South African Airways and with Qantas Empire Airways, with whom the Corporation was negotiating, to loan from them a number of aircraft. Qantas were already operating Lockheed Constellations. BOAC had ordered eight Super Constellations and fortunately deliveries were just beginning. It would make sense for BOAC to lease aircraft of a type compatible with those they were purchasing and thus economise on crew training.

To purchase American produced aircraft required Governmental approval because of Dollar exchange

considerations. The Government indicated that it would, in the circumstances, be sympathetic to further purchases of Constellations, DC6s and DC-M4s.

The results of all the investigations - both by the RAE and de Havilland - were presented to the Court of Inquiry, which met in the Autumn of 1954.

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:) Court of Inquiry

As it turned out, it was the water pressure tests on G-ALYU at Farnborough that unlocked the Comet mystery. After being pressurised and depressurised for the equivalent of 9 000 flying hours, metal fatigue led to cracks appearing on each side of a rivet close to a cabin window. This in turn caused the cabin to crack open and explosively decompress. Based on this evidence, RAE scientists were able to help the Royal Navy locate the part of Yoke Peter that had similarly failed. On being examined at Farnborough, it too was found to bear "the fingerprint of fatigue."

Lord Brabazon of Tara gave evidence as Chairman of the Air Registration Board to the Court of Inquiry -held at Church House, Westminster, London between 19 October and 24 November 1954 - and said

"The Elba accident was completely unexplained to us. The Comet was a machine that was being talked about all over the world, being as it was, the most remarkable machine in the world and if we grounded the type of every aircraft that had unexplained accidents you would scarcely have a machine in the air. The cause of the accident was the adventurous pioneering spirit of our race ...here was a great imaginative project...we were conscious of the dangers that were lurking in the unknown.. of course we gave hostages to fate .. but I cannot believe that this Court, or our country, would censure us because we ventured. Everything in the realm of human knowledge and wisdom was put into this machine .. it is metallurgy not aeronautics that is in the dock.

Certainly no aircraft in history had ever been subjected to such an examination, which would ultimately offer results of the greatest value not only to the British aviation industry but to the whole world, by enabling high speed air travel to be developed with increased safety and efficiency. In analyzing the test results it was clear that the Comet 1s cabin had low resistance to pressure fatigue and that, combined with the aircraft's age, would predispose the aircraft to fail in that area.

The concept of metal fatigue - then little known outside engineering circles - was defined to the Inquiry in terms of a structure - which had an ample reserve of strength when new - failing under its normal working load after a certain length of time. Such a failure could not - with 1950s technology - be easily detected prior to a potentially disastrous fracture but in any complex structure, however perfectly manufactured, there were bound to be points where there were local concentrations of stress. If at one of these points the concentration was such as to exceed the ability of the metal to withstand a stress of this nature then - when it is repeatedly applied - the structure would fracture sooner or later no matter how strong the rest of it might be. A crack might develop from a notch, a curve, an edge or a screw thread.

The Air Registration Board, in 1952 when the Comet received its Certificate of Airworthiness, thought that provided it could be shown that parts of the pressure cabin could be proved to have withstood twice the working pressure that would give an ample safety margin in relation to fatigue. But by the end of 1952 it appeared to have been appreciated that fatigue was more likely to be a serious factor in the case of aircraft relatively highly pressurised - such as the Comet. The ARB. governing aspects of the subject appeared to have been satisfied at the time that - on the information they then had available to them - the maximum concentration caused by pressure loading, under operational conditions, would be only be about 40 to 50% of the ultimate stress strength of the material - therefore there was still a big enough load factor for safety.

However it appeared from the RAE investigation, and their tests on the other Comet airframe, that in the pressure cabin there could be points where there was a loading of as much as 70% of the ultimate stress. That stress had occurred near corners of windows. It was not suggested for a moment that anyone in de Havilland, or the ARB could have known this in 1951. de Havilland made the most of their extensive tests and they had what they believed to be a comparable specimen of the pressure cabin under test which broke down only after 54,000 hours. It was possible that the cabins subjected to this test were not really reliable for the test for without anyone appreciating it - it could in fact be strengthened by having heavy pressure (water) applied to it before the test was carried out. In other words the pre-stressing of the structure by the application of a static load (water pressure) could have improved fatigue life in the test specimen.

The Farnborough tests on G-ALYU, which had already been in service, showed that the cabin had failed at 5,546 pressurization cycles. Translated into structural hours it was equivalent to 9,000 hours. In terms of 'fatigue life' the failure of the test specimen was not unreasonable compared to the hours accumulated by the lost aircraft - Elba Comet 3,681 and Naples Comet 2,701 hours.

The RAE had concluded that the first part of the aircraft to fail was the pressure cabin. Wreckage indicated, furthermore, that this was so. The wings were marked laterally with gold and blue paint and these markings extended across a wing fracture - indicating that the wing was whole at the time of break-up and that it was the pressure cabin that failed first. Similarly markings on the wreckage of the rear fuselage indicted that this was not a primary site of structural failure but followed the disruption of the cabin. Furthermore the RAE were able to demonstrate that the tail section broke away before the nose - this evidence was contained in the type of fracture found in the control cables.

The evidence suggested that the aircraft fractured along the top of the centre line and such was the violence of the event that the structure was thrown sideways and out scoring the wings as it went. Indications were that the primary failure was at the rear of the ADF hatch in the top of the cabin. In tests at Farnborough similar failures had been reproduced. Further a Perspex model of the Comets fuselage, stressed to scale, had been equipped with seats and dummy passengers. Pressurized to 8.25 psi. (40,000ft) the model was ruptured along the top centre line. In 1/10th second there was complete chaos and after 0.5 sec. dummy passengers could be seen hitting the roof with considerable violence.

R. E. Bishop, designer of the Comet, told the Inquiry that he saw no evidence from the many tests, or from the wreckage, to suggest that Redux had been a contributory factor to the failure of the pressure cabin. During production of Dove and Comets de Havilland had made 180,000 test pieces and the integrity of the joints had been repeatedly tested. There had been 425 separate tests for that purpose and now the problem of fatigue in pressure cabins was appreciated nobody need fear that the trouble could not be put right. He had complete confidence in the pressure cabin of the Comet and that it could be made safe and there was no reason why they could not again go ahead with the Comet at full speed.

The Board had already indicated their intention that complete cabins of pressurised aircraft should be submitted to tank tests similar to those used at Farnborough at any rate until knowledge of the fatigue problem was more exact. Before the Certification of certain prototypes could be contemplated a provision would now be required for fatigue testing of entire components. In the Boards view at least two airframes of each type would have to be made available - one for static testing and one for fatigue testing.

Aftermath

The Court of Inquiry ultimately concluded that Comet aircraft could go back into service after modifications and have a very successful career provided a thinker gauge skin was used and there was some strengthening of the fuselage and wings. Indeed, the de Havilland Company issued a statement as soon as the Inquiry was complete outlining their plans for the two later versions of the airliner, the Comet Mk.II and the Mk.III. When work was suspended on them pending the outcome of the Inquiry de Havilland had completed six or seven Comet 2s and construction was well advanced on another 13 or 14. A total of over a million pounds had been spent on these 20 aircraft.

The Company was now faced with the decision as to whether to strengthen the existing fuselages or to dismantle them and rebuild them completely. A total of 32 Comet aircraft were on order - 12 by BOAC and the remainder by Air France, U.A.T., the national airlines of Venezuela, Japan, Canada and Brazil. So far only one prototype Comet III had been built but de Havilland had orders for eleven: 5 for BOAC, 3 for Pan American Airways and two for Air India International and a prototype for the Ministry of Supply.

It was probable that the Comet I was not likely to return to airline service. But one of the important decisions facing the manufacturers was whether, in the interest of good business relations, some form of financial or other form of adjustment should be made to the purchasers of these airliners who were no longer able to use them. The two French companies, Air France and U.A.T. which each bought three Comet Mk.Is had also ordered the Mk.II. The Royal Canadian Airforce had bought two Mk.IAs. BOAC had a total of ten Comet Is of which four were lost in accidents. Three of the remainder were at the RAE, Farnborough, Hants.; one of which has been employed for flight tests, one for general examination and the other for water tank tests. Another BOAC Comet was at the de Havilland works at Hatfield and two were in storage at London Airport.

On November 23, the last day of the Inquiry, de Havilland proposed that the fuselage of the Comets now under construction should be rebuilt. Thicker gauge materials would be used in the cabin pressure area and windows and the cut-outs would be redesigned and strengthened. There would also be a redesigning parts of the Comet wing which were prone to failure fatigue to reduce the overall stress level. Modifications had been devised to the fuel venting system to prevent venting of fuel during takeoff and climb. The Company were also devising a method of preventing damage from pressure-refuelling systems and would consider a modification to the power control system to suit the convenience, and comfort, of the pilot. Investigations would be continued into the use of non-flammable hydraulic fluid and damage from buffeting from the jet efflux would be further reduced by the thickening of the fuselage skin. Door hatches liable to damage from passengers and freight would also be reinforced .

Sir Hartley Shawcross, counsel for De Havilland at the Inquiry also said that -

de Havilland made their stress calculations in 1946. Aircraft designers were not alive to the risk fatigue in pressure cabins and, looking back now, the Company entitled to say that not only had their calculations and tests been above the standard set by every authority but they had demonstrated that there could not have been stress in the pressure cabin of more than 50%. It had therefore been reasonable to assume that the structure was statically strong.

In any case the lessons were learned. The skin of later Comets was to be some 80 percent thicker than on the Comet 1 (19 gauge not 22 gauge sheet). In fact it could be said that out of the Comet experience all the modern approaches to fatigue prevention and routine systematic examination were devised. The principle was that all structures, wherever possible, should be fail-safe.

Comet resurrection

The Royal Canadian Air Force Mk.1A Comets - purchased for military transport use were - after many successful operational flights - reluctantly taken out of service as a result of the grounding of the Mk.1. They were initially put into storage at de Havilland's Canadian factory at Downsview, Toronto in April 1954. Following the Court of Inquiry most Comet 2 pressure hulls were re-built with heavier gauge skins and in addition their jet-pipes were 'swept out' to reduce buffet. These changes were incorporated into the two RCAF 1As at Broughton, Chester, the first of which arrived on 24th May 1956 after a night-stop at Goose Bay. The modified 1As were designated 1XBs. Once the modification were completed it was intended that the 1XB's be ferried back to Canada by John Cunningham and crew. The cost of the work was put at £142,000.

An Air France Comet Mk 1A eventually passed to the RAE with the civilian registration G-APAS and later joined the RAF as XM823. Today it is preserved in BOAC colours at RAF Cosford Aerospace Museum in Shropshire but back in 1954 the first RAF Comets were Mark 2s.

These featured four Avon 503s, rated at 7300 lb.st. The installation of the Avon necessitated enlarging the engine air intake ducts - which gave the Mk.2 a distinctive appearance. These modified ducts were first seen, along with the revised leading edge, on G-AMXA, the first Series 2 production Comet, in January '54. Fuselage length had increased by 3ft (0.91m) to give 96ft 1 inch (29.28m). The span remained the same as was height. Wing area was marginally up at 2027 sq.ft. Gross weight: 120,000lbs (54545Kg) and range, would give a practical stage-length of 2200 - 2400 miles (3520-3840Km) with usual airline reserves.

The Comet 2 now had genuine South Atlantic (but not North Atlantic) capability. Extensive test flights with G-AMXA confirmed true long-range capability. In January 1954, en route for tropical trials, 'XA set a new point to point record between Hatfield and Khartoum of 6hrs. 22min. 7.2 seconds for the computed distance of 3064.1 miles (4902Km) at an average of 481.1 mph. Onboard were crew members John Cunningham and Peter Buggé of de Havilland with Capt. A.M.A. Majendie and Capt. H.J. Field from the Corporation, along with representatives from the ARB and Rolls-Royce. 'XA demonstrated that, even with less favourable weather conditions, impressive stage lengths could be flown on normal tankage. This was to bode well for RAF Transport Command. The tropical trials in Khartoum were followed by high altitude work from the Jan Smuts Airport at Johannesburg which, with an above sea-level altitude of 5,559ft (1694m), enabled high-altitude takeoffs and other testing.

The whole series of African tests was scheduled to last only two weeks because the bulk of testing had been completed in May 1953 with the Avon 2X - which was also flown to Khartoum and Entebbe for tropical trials. Parameters evaluated included normal and engine-out takeoffs. Accelerate-stop distances would be measured with those for all-engine and engine-out climbs as well as baulked landings. Cruise control techniques were evaluated on various inter-stage flights. On the South African route Jan Smuts, Johannesburg was the highest airfield.

Later BOAC decided to operate via Nairobi - at 5,380ft (1,640m). More importantly, it had a runway only 7,980ft (2,432m) in length. So at Nairobi the Mk.2 would have to be operating with a low AUW to be sure to get airborne especially at high ambient temperature. To get round this problem it was decided to schedule Nairobi via Entebbe - a short stage-length of only 317 miles(507Km) and so the fuel load, and consequently AUW, could be kept low.

Once the tropical trials had been completed the bulk of the work for ARB Certification had also been completed. A total of eighteen Comet 2s were eventually completed - though three of these did not fly. Eventually it was decided that all Comet 2s - then on the production line - would be allocated to the Royal Air Force.

Ten Comet C. Mk.2s - with strengthened freight doors - were destined for 216 Squadron. They would be fully ARB certified, have full cabin pressurisation and so would be able to carry troops and other passengers. In addition there would be three unmodified aircraft - Comet Mk.2 R - for reconnaissance duties with RAF 51 and 192 (Signals) Squadrons which would only be capable of limited pressurisation. Finally there would be three unmodified incomplete aircraft for fleet reserve and two flyable examples of Comet T Mk 2 for training.

The 16 aeroplanes listed above cost the Government a total of £4,068,000 which included £1,188,000 for sixty-six Avon 200 series engines for use in the Mk.2s. In addition two more examples were required, at a cost of £555,000. One a modified test specimen for testing in pressure tanks and one a modified aircraft for routine tank testing.

In addition, variants of the '2' had an enormously important series of tasks to perform in research and development - often with BOAC - for crew training and route evaluation too. G-ALYT - fitted with an Avon 524 (R.A.29), had a special water rig assembly attached just forward of the air-intake and was used for de-icing tests.

Comet Mk.2Es

Two Comet 2s were destined to serve 'over and above the call of duty'. They became development test-beds for the Comet 4 program. Mk.2s G-AMXD, and G-AMXK were both modified by having the outboard Avon engines replaced with the latest more powerful variant - the 524. These Mk.2s were designated the 2Es. External modifications were necessary and 2Es featured enlarged intakes at the outer positions. 2Es were used to evaluate the RA29 engine that was destined for Comet 4. It was necessary to build up the certified overhaul life of the engine. The ARB required a minimum life between major overhauls of 1000 hours per engine. Each stage of development had to be authorised and an engine would be certified for, say, 200 hours initially but with ARB approval given for extension up to 500 hours operation. Once proved at the higher figure the certification would extend the 'extension'. And so on.

Each engine was returned to RR for stripping down and wear analysis as they reached successively higher accumulated hours. The first two engines were returned after 250 hours. The third was returned after 350 hours and the forth after 450. 600 hours was the next target and so on.

Between September 1957 and early in 1958 the certified life of 524 was extended from 200 hours to 750 hours - in fact by May 1958 some 7000 hours had been accumulated. Rolls-Royce were confident that by the time the Mk.4 was due to enter service 1500 hours would be achieved but, in the meantime, the ARB had approved an extension to 1000 hours for one 524s in each 2E.

Comet Flight

The 'Comet Flight's' objective was speed Avon development while the crew training program got underway. It was decided to provide the Corporation with two 2E's - the first being delivered on 26th August 1957. This was flown from Hatfield by Capt. A. P. W. Cane, who was to reform the 'Comet Flight' which had been suspended in 1954. The Corporation decided to purchase 'XK outright. 'XD remained the property of the Ministry of Supply. The 'Flight's' team comprised three complete crews and two extras. Ten captains and four engineering officers attended technical courses at Hatfield and Rolls-Royce at Derby. Deputy of the 'Flight' was T. B. Stoney while H.J. Field had responsibility for performance assessment; Eng./Off. J. Kingston handled engineering and radio matters were in the hands of R. J. Dolman.

BOAC's plan called for the accumulation of 3500 hours before the end of May 1958 so 'Flight' they were putting in six flights a week, each averaging 11½ hours! As more crews became available development accelerated.

The 2E performed excellently and the Corporations targets achieved. By January 1958 their 2Es had achieved 1500 hours on proving flights. Also revised were Comet Mk.1 jet holding patterns, climb and descent procedures, cruising techniques, and the 2Es were later used extensively during the evaluation of the Decca/Dectra navigation system.

This system was planned for the transatlantic Mk.4s. There had been much rivalry between the British Decca system and the less sophisticated Vortac system from the USA. The American Loran C - similar to Dectra - was not yet up and running and so the choice was relatively simple.

The MoS 2E G-AMXD equipped with Dectra had been giving a series of demonstrations in an attempt to convince airlines and CAA of its merit. Dectra equipped 2Es were operated on the North Atlantic routes and provided accurate en route tracking and lateral separation.The Ministry of Supply 2E 'XD was returned in May 1958. In June BOAC switched their own aircraft 'XK to transatlantic proving flights to gain valuable operational experience on the North Atlantic route. Schedule jet services were planned from the autumn.

This program ran in three phases:-

Eleven daily return flights to Gander routed west-bound via Keflavic.

Eight three day trips, the first day to Gander, the second day flights from Gander to Goose, Stephenville, Sydney, Moncton and return to Gander, third day back to London.

Eight further trips beginning as on day one of Phase 2 to Gander but then on day two practicing approach and let-down procedures at Baltimore, Montreal, Boston and New York.

This series of transatlantic flights added 423 hours to BOAC experience.

G-AMXD was re-registered as XN453 and joined the RAE, Farnborough for 'radio development' work. G-AMXK was modified to test auto-pilot and automatic landing systems for Smiths Industries (destined for use in the DH 121 'Trident') and later - in 1966 - it found itself at Blind Landing Experimental Unit (BLEU) as XV144. It was used for spares for XN453 when it retired in 1970.

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:) .Comet 4

.

History was made just over four years after the Comet Mk.1s were withdrawn from service. The first series Mk.4 (G-APDA) made its maiden flight on 27th April 1958 at Hatfield. It was airborne for 83 minutes and was crewed by John Cunningham (Chief Test Pilot), Peter Buggé (Chief Development Test Pilot), E. Brackston-Brown (Chief Flight Engineer), J.L. Johnson (test flight observer) with J. Marshall (instruments observer).

The Comet 4 was a completely new aeroplane: one with over 50,000 hours of test and operational flying and a programme of scientific proving and ground testing which was unprecedented in aviation history, behind it - 80%, of which had been completed, with the Mk.3.

Comet 4 simply had to be the safest aeroplane ever to fly. The test-rig programme set up to investigate the fatigue failures had continued to work with a view to gaining more information about both materials and new anti-fatigue design concepts. The program was then re-directed to test new components for the Mk.4. Once the designers were satisfied that particular components met their 'new' specification they were incorporated into a 'whole' structure, e.g., into a complete wing. This was then rig-tested, eventually to destruction. Component testing covered materials, windows, canopies, the centre section and spars as well as the undercarriage. All seams and joints were carefully investigated for soundness or signs of impending failure.

All this was necessary because the aim of de Havilland, and the ARB, was to ensure a safe-life for the Comet above its useful operational life - assuming the latter was not less than 30,000 hours. To achieve this exacting requirement components were often tested to factors of 5 times (as in the case of the wing) or 6 times (for the pressure cabin) in excess of this 'life'.

The effectiveness of this programme was demonstrated when, at a later stage, it was decided to produce the short-medium range Comet variant - the 4B. This aircraft would be subjected to greater stresses than long haul types because it would have to operate in more turbulent conditions prevalent at lower altitudes and make many more frequent takeoffs and landings. The basic structure proved to be extremely robust - so much so that the 4B only needed minor modifications.

de Havilland had learned that, in practice, it was not always possible to design components to be fail-safe but, wherever it was possible to do so the company adopted that approach. Sometime though a compromise was necessary and a 'safe-life' for any component or structure would have to be demonstrated.

The number of changes incorporated into the Mk.4 were enormous. They reflected not only the experience gained with Comet 1 but also, after a gap of some eight years, the many new concepts and practices that evolved since. An example, and this was due to experience gained directly from the Comet 1, it was not sufficient just to cant outwards the engines jet pipes, for the Comet 4 there had to be extensive modifications to the rear fuselage to enable it to withstand better the effects of jet-blast. The tailplane and elevators too were given thicker skins and the ribs doubled-up to help withstand the 'noise' vibration induced by the turbo-jets. A new 'aged' aluminium alloy (24ST) was used on the lower tension surfaces of the wings and, on the same theme, Zinc-alloy sinks were eliminated from the fuselage. Much stronger steel lug-forgings were used for the attachment of the wings and tailplane etc. In fact the Comet 4 differed in almost ever respect from the Comet 1.

Many lessons were learned too with the operational Comet 1 with respect to aircraft systems. As a result many changes were incorporated into the Mk.4. For example, electrical distribution was by separate busbars backed up with separate emergency busbars. More powerful alternators were used at 350 amps and all the electrical equipment had been explosion tested! Problematic multi-pin plugs had been eliminated where possible and American type connectors, inverters and terminals were now used. The Comet still featured fully powered flying controls but modified with adoption of 'Q feel' The system gave an artificial feel to the controls proportional to airspeed. The system was applied to the elevators and also used to restrict rudder movement above 180 knots (this was done because too much rudder application at speed could induce excessive yaw and thus induce possible over correction). The system was not applied to the ailerons. Detail changes e.g. to reducing friction within the control system resulted in the criticised break-out force of the Comet 1 being halved to around 10lb.

In the Comet 1 the crew had to manually compensate for trim displacement when using the autopilot. The Mk.4 had the Smiths S.E.P.2 autopilot which automatically adjusted the trim. Also new was an automatic approach (I.L.S.) coupler included in the autopilot system. A stick shaker had been added to give warning when a stall was imminent - this was far superior to the previous stall warning indicator i.e. the whole airframe shaking! This stick shaker, and alterations to the elevator gearing (making displacement of the stick greater during takeoff and landing - i.e. more coarse - than during normal flight), had been incorporated into the Comet 2 also.

A Mach sensitive device (which had been devised for the French and Canadian Mk.1As) was incorporated into the elevator circuits which applied an amount of up-elevator when a pre-set Mach. number was reached - in this case 0.77M. Other safety features included duplicated powered input and output control of the elevators to guard against system failure. To this end too power to the ailerons was duplicated - in fact all the major control systems and undercarriage had duplicated hydraulic supplies Also revised were the recommended flap settings and there was the addition of a yaw-damper.

AiResearch experience had enabled Normalair to produce a very sophisticated pressurization and

air-conditioning system for the comet 4 - and it was to a great extent was automatic in operation. Once the altitude at which pressurization was to begin was determined and set, such things as temperature, air mass-flow, air recirculation and rate of climb were automatically dealt with. There were special cold-air units incorporated into the system and these were made by de Havilland Propellers under licence. De-misting was taken care of by having gold-film heating elements embedded in the cockpit glass.

The Avon engines were protected by a new anti-icing system as was the airframe. These revised systems had been extensively tested on the Comet 2X. In the cockpit the black background to the instruments had been replaced by the fashionable grey - which was said to make the instruments and controls stand out better. The engineers panel had been revised with the various banks more logically arranged. For the 4B and 4C the pilot's windscreen panels were made some 4 ins. deeper and greatly improved visibility.

The fuel system too was extensively revised and, as in the Mk.1, each engine had an independent fuel feed. New safety pressure-relief valves now protected the pressure refuelling system. Fire safety had been a particular concern of the American Civil Aviation Authority because of the Comet's buried engines. R.R. built a special test 'fire tunnel' at Huchnall to demonstrate the extinguisher systems. Rolls-Royce developed noise suppressors for the jet pipes and were developing thrust reversers - at this stage only tested on the Comet 3 (Note: a prototype thrust reverser had been demonstrated in tests on the 2X).

All these modifications made the Mk.4 far superior to its predecessors. For the passenger too a new 'bright' revised cabin interior added to the sense of luxury and was more than a match for its rivals. BOAC were planning to carry 16 passengers, four abreast, in seats with a pitch of 56 ins. in their deluxe class cabin and 43 passengers, five abreast, at 40 ins pitch in tourist class. The spacing was generous by any standards.

Range was now 2720 nautical miles in still-air at maximum AUW, initially 156,000lb with reserves Optimum cruising speed was 505 m.p.h. (438 Knots) at 28,000ft when the rate of fuel consumption would be 9,650lb/hr. Cruising altitude in excess of this was often used, 36,000ft being typical.

So the Mk.4 had North Atlantic capability. However a stop-over was necessary in most cases operating westbound. Capacity payload was 20,286lb and gross weight, less fuel and payload 75,424lb. Max. takeoff weight was 158,000lb (it was gradually increased in stages to 162,000lb) and landing weight 120,000lb. Cabin volume was 2,815 cubic feet with a freight/ baggage volume of 570 cu.ft. The usable floor area was 439 sq.ft in a fuselage with internal dimensions 71ft 8in long, maximum width 9ft 7in and height 6ft 6½in. The Mk.4 would accommodate - as a typical mix - 24 first-class passengers and 43 tourist class. Capacity depended on pitch adopted and number of seats abreast. In Deluxe class with a four abreast/ 56in pitch seating could be provided for 40 passengers. In first-class 40in pitch for 56 passengers; or five abreast/40 in pitch for 71 tourists; and finally Economy class with 34in pitch for a cramped 81 passengers. Power came from four RR Avon 524s (RA.29/1) which were rated at 10,500 lb.st each. Fuel capacity was 8,898 Imp. gallons (the pod tanks each held 440 Imperial gallons)

From the outset it was planned to set up a second production line. This was done at the Hawarden

Aerodrome, Chester - which was part of the de Havilland Company. In fact fourteen of the nineteen Mk.4s for BOAC were to be built there. In all 16 Mk.4s, 2 Mk.4Bs, 9 Mk.4Cs and 5 C.4s were built at Chester.

The Air Registration Board had spent more than 10 flying hours in the Comet Mk.3 on certification work.

Limited certification had been granted for the Mk.4 to enable training and route proving flights to begin. The ARB still required, however, another 250 hours of test flying before full certification would be granted and 100 hours of that had to be under operational route-proving conditions. In practice basic evaluation by de Havilland took few flying hours - such was the accuracy of the Mk.3 data. Some new systems (not found on the Mk.3) were adopted for the flying controls and these, and their new emergency back-up systems, were relatively easily assessed. There were no problems.

Route proving therefore took up most of the necessary 250 hours for the ARB and BOAC were well placed and ready to put the Mk.4 to use. BOAC had at a late stage decided to have emergency passenger oxygen supplies fitted before their scheduled services were due to start. This was already a requirement in the U.S. The Comet system was designed by Walker Kidde Ltd. and in use the masks automatically spring from the hat-rack in the event of decompression.

de Havilland meanwhile undertook a series of their own long distance certification trials/demonstration flights. With G-APDA, for example, John Cunningham covered a distance of 7,925 miles on route from Hong-Kong to London in a flying time of 16 hrs 16 min. - average speed of 487 mph.

During August 1958 G-APDA returned form tropical trials in Africa at Khartoum, Wadi Halfa, Nairobi, and Entebbe. Towards the end of August 'DA made history crossed the North Atlantic New York to Hatfield in 6 hrs and 27 min. knocking 1 hr. 17min off the previous record! Crew: John Cunningham, Peter Buggé and Peter Wilson joined by BOAC pilots Capt. N.A. Mervyn-Smith, Ward and C.T. Farndell. September saw 'DA fly out to Hong Kong for route proving and for a special occasion too - the inauguration of Hong Kong's new runway at Kai Tuk. On the return flight further records were set - a distance of 7925 miles in an elapsed time of 18 hrs. 22 min with two refuelling stops at Bombay taking 1 hr. and at Cairo 1 hr. 6 min. The final de Havilland demonstration / test flight in G-APDA added 48 hours to the ARB total covering 23,000 miles in ten days via Ottawa, Gander, Toronto and to de Havilland's Canadian factory at Downsview. Vancouver, Mexico City, Lima, Buenos Aires, Rio de Janeiro, Caracas and then on to New York and from there a non-stop flight to Hatfield.

On this tour some 600 people flew in the Comet. Records were set on every sector it flew. Later when asked about the Comet's serviceability record John Cunningham said that on the third 23,000 mile tour there had been no snags of any kind. All that had been required was fuel and three pints of oil! On the previous flights too reliability had been excellent. There had been only one minor snag - and that was the failure of an electric actuator. The aircraft had also demonstrated its ability to rely on its own batteries for starting in the absence of ground power supplies.

In September 1959 de Havilland announced an increase in the payload weight of the Comet Mk.4 and Mk.4C from a certified 158,000lb to 162,000lb. This increase (without increasing the tare weight) had been made possible by adopting the 4B stub wing for the Mk.4 and 4C. Carriers could either extend the range with capacity payload or increase payload over longer stages.

On September 29th 1959 the Minister of Transport recommended that the ARB issue a C of A for the Mk.4. The following day - on schedule - de Havilland delivered G-APDB and the second production G-APDC to London Airport for the hand over. Present at the hand over ceremony was the Minister - Mr. Aubrey Burke - who brought with him the Certificate. This he duly handed to Sir Geoffrey de Havilland who, in turn, handed it to Sir Gerard d'Erlanger, Chairman of BOAC.

BOAC transatlantic services began on Saturday October the 4th. Just before Pan American introduced

transatlantic scheduled services. However, Comets were only destined to ply the North Atlantic for two years. Overwhelming competition for America had arrived.

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Alan,

Do you remember when the (I think DC3) crashed into the upper floor of the house, in Gloucester, at the corner of Stroud Rd and Tuffley Ave.

I still have vivid memorys of the main fusilage sticking out of the side wall.

This would have been in the early 60's.

Any info on it.

Nobby

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Hi Nobby! Yes, that Tuffley crash has become something of a legend and I will give you a full report as soon as I have looked into my research material! In the meantime though, here is the end of the Comet story. I hope you have enjoyed it!

On 15 July 1954 - during the Comet 1 fleet grounding - the Boeing 707 -80 made its maiden flight at Renton near Seattle. Featuring a skin four times thicker than that of the Comet 1, the " dash 80" was powered by four gas turbines developed from engines of America's B-47 and B-52 bombers. Like its military forbears, - and the Messerschmidt 262 - the Boeing 707's prime movers were in pods beneath the wings. By 1958 the new jet airliner had, like the Comet, developed intercontinental range and could carry more than twice as many passengers. It had also been bought by Pan American and KLM and would eventually be bought by BOAC. In fact the Boeing 707 became the most widely used airliner in the World between 1960 and 1972 and spawned the even more successful 727, 737 and 747 series of jet airliners, although de Havilland for one did not intend to take this competition lying down.

Comet 5 - the airliner that never was.

Just at the time that de Havilland was well advanced with Comet 4 production informed industry observers were speculating on its successor. Talk was of a major re-development of the Mk.4 - designated 'Comet 5'. This was not in fact pure speculation - there had been discussions within the Company about future projects - including a long-range airliner - but nothing further than that had been done. In this respect de Havilland had four options. To develop the Mk.4 further generally increasing its size and range; to start from scratch and design a new long range jet airliner in house (now as part of Hawker Siddeley); to collaborate with another manufacturer on a similar project (Boeing was a possibility) or to abandon their tentative plans to produce this class of aircraft at all.

At this time there were several reports in the press claiming the existence of the Comet 5 - and, naturally, associating it with BOAC. Perhaps fed by Company leaks, the general consensus of opinion was that the aircraft would be based on the Mk.4 but would have a new design of wing, with greater sweep, to give it higher cruising speeds and to incorporate four R.R. Conway engines installed in pods (as per 707). It was suggested that such a machine would be developed for service in the mid-1960s and that it would be done with the backing of BOAC.

D.H.118 was a design development based on a previous exercise known as the Comet 5. This design featured four pod-mounted R.R. Conway engines. With a projected cruising speed in excess of 550 m.p.h. and a range of 5,000 miles in still air it could provide a London - New York service - even against the prevailing westerly winds - and still have adequate reserves of fuel. Although the company would not admit it a considerable amount of time was spent on this project. In talks between Aubury Burke and Sir Miles Thomas it was clear that de Havilland had the Corporations full backing for the development of the Comet 5. Sir Miles was very enthusiastic about the project.

The project envisaged retaining all the parts of the Comet 1 and 2 that would have been costly to redesign e.g.control systems, flight deck instrumentation, pressurization system and any equipment that had been thoroughly tried and tested. The fuselage would have a thicker skin and would have been widened by inserting a 9 ins. gusset and it thus would be able to seat five abreast in reasonable comfort. Furnishings such as the galley, toilets, doors and windows would be reused. In addition to pod mounted engines the angle of sweep of the wings would have been greater - and thus give a higher maximum speed. In fact it bore a striking resemblance to what was to become the Boeing 707.

Sad to think that with appropriate backing Comet development could have naturally followed that route. After a heated discussion with the then Minister of Transport - Harold Watkinson - the Minister refused to approve the project. At the hands of the Ministry the project died. In truth the Ministry of Transport did not seriously consider what BOAC really wanted. The new Minister of Transport was determined to make his own decisions and not to be influenced or encumbered by any previous Ministers' inclinations nor apparently by what his rival at the Ministry of Supply thought logical.

Sir Miles concluded later that he should have fought harder for the Comet 5 for it would have had a profound effect beyond that of meeting the fleet needs of BOAC. As it happened Britain would have saved a considerable amount in Dollar exchange, the world would have see Britain build upon it's short-held lead in commercial jet transport and the whole country would be given a much needed boost to morale.

The footnote to this story was that on March 8th 1956 Sir Miles Thomas tended his resignation to the BOAC Board. On the 24th October 1956 BOAC, with government approval, placed a record order for 15 707-436 aircraft. The irony is that the power-plant specified was R.R. Conway 508 of 17 500 lb.thrust.!!! It seems that for whatever reason the Ministry had wanted the Boeing all along.

Comet 4s in South America

Aerolineas was founded in May 1949 when the Argentinean Ministry of Transport merged the carriers Fama, Alfa, Aeroposta and Zonda. Aerolineas Argentinas took over all their existing routes and during its first ten years of operation was rarely out of financial difficulties. Brigadier General Fabri, who was President of the Argentine Air Transport Association, claimed that the airline was, "one of the biggest money losers in the world". It was said that the airline had lost £1.400,000 the previous year (1958) yet, despite this, they had made a £9,000,000 commitment to purchase six Comets Mk.4.

In fact the order for Comets was made in order to help in Aerolineas's attempts to regain solvency. In South America, as anywhere, the simple fact was that any airline operator that failed to compete with foreign carriers, if necessary by using the new jet transports, was bound to suffer. The major United States airlines were about to introduce the Boeing 707 on their South American routes - Aerolineas Argentinas was obliged to respond. Strangely, in May 1960 the Argentineans hit the headlines once more because of another 'financial' incident - but this time it was a dispute to which Aerolineas were not directly a party.

One of their new Comet 4Cs was seized by the Italian Authorities after landing at Rome Airport. A Milan court had given an order for the seizure following court action by an Italian industrialist, Franchesco Gronda, against the Argentine Government. It seems that £11.5 million was owing for the construction of an aluminium factory in Argentina. The court released the aeroplane two days later.

There was much concern in Hatfield after another change of Government in Argentina when it became known that considerable pressure was being exerted to force Aerolineas to cancel their order for Comet and buy Boeing 707s (or 720s) in their place. To make matters worse these events happened to coincide with further reports in the financial press of more heavy losses by Aerolineas - said to be £2,500,000 the previous year. However the new Government declared that it favoured a policy of 'continuity' in the field of foreign trade. Aerolineas found it had friends in high places - Government departments, members the Air Force and Navy as well as President Frondizia - all gave the order their support.

Most countries set great store in the prestige conferred by having their own airline and Argentina was no exception. Aerolineas would show their South American neighbours, with whom there was an intense and sometimes bloody rivalry, that they were the leading airline on the continent, the only South American carrier to have their own jets. Further Aerolineas would be carrying the flag into the more remote parts of the area, and such were the particular operating characteristics of the aeroplane that, often they were able to schedule the Comet into airfields that could not accommodate the Boeing 707 or DC8.

By the time the first Aerolineas Comet 4 was being readied to be rolled out at Hatfield, sixteen Aerolineas aircrew were already completing a seven-week training course at Hatfield. Their senior pilot was Capt. L. A. Fortin. Registered LV-PLM, the first aeroplane of the order made its maiden flight on 27th January 1959 and, the same day, was officially handed over to the airline. By March 2nd LV-PLM - soon to be re-registered LV-AHN - had completed its production test flying and crew training programme and was ready to set off on it's delivery flight home to Argentina. Piloted by Captains S. Llense and A. Aguirre the Comet flew via Dakar, Recifé and on to Buenos Aires - a distance of 7075 miles, which they completed in 18 hours elapsed time.

The second Aerolineas Mk.4 LV-AHO (initially registered LV-PLO) made its first flight on 25th February 1959 with Pat Fillingham and L.E.F.Young amongst the crew. It was delivered to Buenos Aires, with Messrs. Buggé and Young, setting off from Hatfield on 18th March - the flight doubled as a promotional opportunity for de Havilland. Lengthy stopovers were made at Paris, Frankfurt, Amsterdam, Rome, Madrid and Lisbon - at each city, two demonstration flights were flown. The journey to Buenos Aires continued via Dakar and Recifé and the Comet arrived in the Argentinian capital on 25th March.

To sum up re-registrations: On 2 March1959 LV-PLM became LV-AHN 'Las Tres Marias'; LV-PLO became LV-AHO 'Cruz del Sur'; and in May LV-PLP became LV-AHP 'El Lucero del Alba'. More training and route proving flights took place during March and early April leading up to the inaugural scheduled

flight from Buenos Aires to Santiago, Chile. The 850-mile hop was completed in a (then) record time of 1 hr 49 min.

The third Mk.4 - LV-AHP - was delivered on the 2nd May 1959 to Buenos Aires (BA) by Pat Fillingham, de Havilland Chief Production Test Pilot - accompanied by Aerolineas Captains Aguirre and Llense.

Soon all three Comets were fully employed training, route proving or operating commercially. Aerolineas Argentinas planned to commence services to London on 19th May - beating BOAC who had advanced plans to service the route themselves. BA to New York was scheduled to begin on 29th May. de Havilland training crews accompanied many of these 'new' flights.

On 8 May Aerolineas signed a contract with BOAC whereby the Corporation would provide maintenance facilities for them in London, Frankfurt, Rome and New York. It was the first contract of its kind between the two rival carriers. However there were no other commercial arrangements with regard to Comet 4 services between the two operators, after all, they were eventually planning to be in competition with each other on a number of routes between BA and Europe.

The interior of the Aerolineas Argentinas Comets differed from those of BOAC - the purchaser could always select their preferred options when it came to furnishings. For example, Aerolineas's first class seats were designed and fitted by de Havilland and were built by Lancefield Aircraft Components Ltd. Whereas the tourist seats were supplied by Aircraft Furnishing Ltd. The cabin was styled by Charles Butler and provided for 24 first and 46 tourist class passengers.

An operational problem arose in August 1959 when Aerolineas were refused Comet 4 landing rights at Rio de Janeiro, which of course was one of their principal destinations. The Brazilian Government claimed that Comets were damaging their runway! In fact this refusal probably owed much to the fact that Aerolineas had criticised the condition of the Rio runway on a previous occasion. Brazilian pride was hurt and the refusal of landing rights was their immediate response. Of course it was nonsense. The Argentineans pointed out in the Comets defence that the aircraft had been using many of the world major airports for more than a year and that there had been no reports of runway damage anywhere else. Eventually the Brazilians gave way.

The second phase of Aerolineas Argentinas expansion was to take place with the delivery, by the mid-1960s, of the remaining three Comets. LV-AHR, originally named 'Alborada', was re-named 'Arco Iris' and LV-AHS, originally 'Las Tres Marias', was re-named 'Alborada'. Both aircraft were delivered in March 1960. The third Comet 4, LV-AHU 'Centaurus', was delivered in July 1960.

So the Argentinean airline purchased a total of six Comets. Three of these they lost in accidents - LV-AHP was damaged beyond repair after hitting a hill-top near Asuncion, Paraguay on 26th August 1959 when it made a forced landing in bad weather. It was carrying 54 passengers and a crew of eleven and was on a flight from Buenos Aires to New York. The very experienced Capt. S. J. Llense was killed and an elderly woman passenger died of shock in the accident.

Soon after the crash the possibility of salvage was assessed but the wings and nose were too badly damaged. Snr. José Guiraldes, President of Aerolineas Argentinas said, soon after, that the cause of the accident was not known but it could have been much worse but for the ruggedness of the Comet and the skill of the pilot. No official report was ever released on the loss.

LV-AHO was destroyed after a heavy landing at Ezeiza Airport, Buenos Aires while on a crew training flight on 20th February 1960.

LV-AHR was destroyed when it hit a clump of trees on takeoff from Vira Copos Airport, Campinas, Brazil on 23rd November 1961. Campinas is 240 miles from Rio de Janeiro. The aircraft was en route from Buenos Aires to New York - and appeared to have been returning to the alternative runway for an emergency landing after a fire had developed in a wing. 40 passengers and the crew of twelve were killed in the accident, which occurred at 03.00 hrs. It seems Campinas was used as an alternative to San Paulo because it offered longer runways and better flying weather conditions. The cause of the accident was to remain a mystery because there was no evidence of any airframe or engine malfunction prior to the crash and, again, there was no official report into the accident.

Despite these incidents the Comet proved to be a great success for the airline and by September 1959, on their North American route, load factors had risen from 49% to 86% following the Comets introduction. Interestingly it had risen only 6% on their European routes, that is, on routes already well served by jets. As a status symbol the Comet was unmatched. On November 26th 1961 President Frondizi set off on a 32-day world tour in a Comet setting out from Buenos Aires.

Underlining their commitment to the Comet, Aerolineas Argentinas signed a contract with Heenan and Froude Ltd. of Worcester in January 1963 for the installation of a Rolls-Royce Avon test facility. It was said to be one of the most comprehensive engine test facilities in use with any airline in the world. It featured a fully sound-proofed test house and could handle turbojet engines up to 30,000lb thrust. The airline was clearly planning for the future.

In 1962 a Mk.4C became available when M.E.A. failed to take up an option due to financial problems. In August 1961 this particular aeroplane had been registered G-AROV by de Havilland. Aerolineas took over the order and it was delivered to Argentina on 27th April 1962 as a replacement for one of their lost aircraft. Initially registered LV-PTS it, like the other Comets, had its registration changed the following month to LV-AIB and named 'President Kennedy'.

LV-AHN, LV-AHS, LV-AHU and LV-AIB, after many years of successful operation, were all eventually sold to Dan-Air, London between October and December 1971.

Aerovias Ecuatorianas C. A. or 'AREA' was founded in 1949 and began operations in 1951 when it took over routes formerly worked by Aero Transporte Ecuatoriano and Transandia Ecuatoriana, both of which had their base in Quito, Equador. The fledgling airline had great plans and in March 1966 announced that intended buying - with a lease purchase arrangement - two ex-BOAC Comet 4s. In the event only one Comet was delivered. In March 1966 a Mk.4 Comet, formerly registered G-APDI, it found its way to AREA via the Mexican Airline, Mexicana. Being existing Comet operators, the Mexicans were familiar with the process of getting their aeroplane certified by the Federal Aviation Authority. Mexicana was the obvious choice to undertake the necessary modifications. The Comet was re-registered HC-ALT and saw service in and around Equador until it was withdrawn in 1968. For a while the aircraft was stored at Miami and after a number of 'nominal' owners it was broken up in 1978.

CAUSA were reported to have bought an ex-BOAC Mk.4 in 1967. Probably the sale fell through. The aircraft concerned - G-APDN - was leased to Dan-Air, London in October 1967 and was finally sold to Dan-Air in May 1968.

In mid-1960 it appeared a distinct possibility that a plan to form a large supranational airline in South America would go ahead. The proposal was AEREA Latinamericanas be set up to replace some smaller carriers and their assorted fleets be augmented, or replaced, by purchasing Comets. The Comet was much liked in South America - it had ideal characteristics for their routes and they envisaged it operating a 'premier service' to oppose the increasing number of U.S. based carriers.

FALA was a projected union of non-IATA member airlines of Chile, Columbia and Peru, they also wanted to get Aerolineas of Argentina to join. It was suggested that Aerolineas would join if the other airlines would purchase Comet 4s so that the group's equipment could be standardised. It was said the de Havilland had approached FALA with an offer to supply 6-8 Comet 4s at competitive prices with early delivery (although the manufacturer would not confirm that).

Almost in the USA

'CAPITAL AIRLINES PURCHASE COMETS' was the headline in the Enterprise magazine - the internal magazine of the de Havilland Company. It referred to a (then) recent joint announcement by Capital and de Havilland, which disclosed an order for 14 Comet aircraft. Thus it appeared that de Havilland had done what every other non-American manufacturer needed to do, broken into the United States airliner market in the face of home competition. The argument went: with a foot-hold in the U.S. market many more 'knock on' sales could be hoped for. So the announcement was of very great significance. The agreement specified that the Comets would be powered by Rolls-Royce engines and, including spares, the cost was put at some £19 million. Deliveries were to commence in late 1958 with four Comet Mk.4s and late in 1959 with ten of the special variant the Mk.4A. J.H. Carmichael, who was President of Capital Airlines, said of the deal,

"The decision to purchase the Comet has been made after a most comprehensive and detailed study of all flight equipment either in production or projected, both in the United States and England. The economical and operating characteristics of the Comet 4A are ideally suited to the Capital system. The Comets will go into service on our major and most competitive routes."

Apparently the same basis for determining economic criteria were used when Capital purchased Viscounts. Projections made before the Viscount purchase had proved accurate when it was introduced on Capital routes in 1955. The Comet order was placed because Capital now wanted a range of pure-jets to operate some 200mph faster than anything else they then had in use. Capital was one of the biggest domestic carriers in the USA as was illustrated by figures for 1955, which showed that Capital carried 2½ million passengers over some 31 million miles!

Capital's Mk.4As were to be furnished to accommodate 74 passengers, "in the utmost luxury" by having 68 persons seated four abreast in two large cabins and six in a forward lounge. The expectation was that passengers would be carried in,

"unprecedented smoothness and quietude, even surpassing the qualities of the earlier Comet models while the speed and economy also show a marked advance".

The 4A was to be assembled at Chester as well as Hatfield. Unfortunately the airline suffered sudden financial difficulties and, after a period of uncertainty, it was forced to give up its routes to rival carriers and was absorbed into United Airlines. The foothold into the US market was lost and the Mk.4A was never produced.

Farewell

On 12 February 1974 the last Dan-Air Comet 4 flew over its Hatfield birthplace en route to preservation at RAF Duxford, by which time the type had evolved into the British Aerospace Nimrod martime patrol aircraft, which is still in service in 2004.

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:D

And here is an account of the Comet 4 from an Argentine angle.

The 'unbelievable' aircraft.

By 1959 Aerolíneas had become both Argentina's leading domestic airline and a prominent player in the international market place. As such the Board decided to add the Comet IV to its fleet and join the jet age. President of the company was Juan José Güiraldes, an airforce man who had the inspiration, strength and necessary experience to head one of the most challenging undertakings in the history of Aerolíneas. Argentina became excited. Europe's proximity became nearer. Enrique Bermudez wrote in his book El Cuarto Cometa ( Comet Captain )

'London is now closer than Río Gallegos, Salta farther than Paris'.

The viability of the plan was cemented by the President of Argentina Arturo Frondizi. Bermúdez continues

"on presentation of our report and listening to our argument Frondizi remained silent. Some minutes later he spoke: 'We will buy six aeroplanes, however, the presidency is resolute, you pay for the aeroplanes - we want no commitments."

The Comet was the unbelievable aircraft - it did not use propellers! The development of the aviation industry has been so rapid that the youth of today cannot begin to imagine the impact those extraordinary aircraft had on us - and the revolution it brought to the industry.

We had to get used to a new engine sound and we were led by Aerolíneas into the modern world. We were touching a reality which had not even been dreamt of by the science-fiction authors.

Here, in Argentina, the first ever jet-pilots were accredited in the history of commercial aviation. Moreno Pacheco became Head of the Airline and Miguel Andreau Head of Operations. Backed-up by key men like Luis Kment, Antonio Torroella, Hialmar Aberg Cobo, Guillermo Ríos, Carlos Regúnaga, Ronald Daintree, Carlos Bustamente, Aníbal Aguirre and Stanley Llense: élite employees of the company, all with an outstanding career history.

It was on 2nd March, 1959, that the first Aerolíneas Comet, LV-PLM 'Las Tres Marías' landed at Ezeiza Airport, it had covered the distance in the, then, world record breaking time of 15h 53m (actual flying time). Aguirre and Llense were the pilots, Hugo Cigliutti the in-flight technician, Carlos Busti the navigator, Tomas Bone was Chief Purser, Maria Crespi and Alicia Corallo the cabin attendants. According to 'The Times' newspaper. It departed from London on the brightest and sunniest winter day ever recorded in the 116 years existence of the London Meteorological Office.

Just one more thought. Does Airfix still do the 1/144 scale model of the Comet 4 in Dan Air colours? Please add your sightings here!

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:) The following obituary appeared in the Times of Monday 15 September 2003:

Fred Jones. Wreckage analyst who was involved in important investigations in the early years of jet powered flight. [ 4 September 1920 - 22 August 2003 ]

In a career of 50 years at the Royal Aircraft Establishment, Farnborough, during which he became an expert in wreckage analysis, Fred Jones was involved in some of the most important accident investigations of the early years of jet powered flight. Among his most telling assignments was the leading role he played in the intensive investigation that followed the - at first seemingly mysterious - series of Comet disasters of the early 1950s, events which gave the death blow to Britain's hopes of leading the world in civil aviation.

Before that, Jones had studied the fragmented remains of the swept wing twin-boom DH 110 prototype and his findings enabled the aircraft to be modified in such a way that it was subsequently able to enter service as the Sea Vixen naval fighter.

A man who lived "within the sound of the RAE hooter" virtually all his life, he had witnessed the horrific break-up of the DH 110 in mid air as it passed virtually over his garden during the 1952 Farnborough Air Show. When he saw the aircraft pitch violently upwards, he already had some idea of what might have happened to it, even before getting among the wreckage. His investigation confirmed that the skin of the leading edge of the wing had separated from it, causing the plane to rear upwards with such violence that the engines broke from their mountings, ripping their way out of the fuselage and ploughing into the crowd. It was a catastrophe that claimed the lives of 28 spectators, as well as those of the pilot, John Derry, and his navigator, Tony Richards.

Fred Jones was born in 1920 in Cove, Hampshire, within earshot of the roar of engines from nearby Farnborough. Educated locally, he left school at 14 to join the Royal Aircraft establishment as an apprentice.

In 1941, at the end of his apprenticeship, he became a member of the newly founded accidents section at RAE, thereafter working as a "disaster detective" on cases occurring both in Britain and abroad. At RAE his habitual place of work was at the "Aeroplanes' Graveyard", three sombre black hangars to which the mortal remains of crashed aircraft were brought from all over the world for reconstruction and examination.

The war provided a flood of work for the new section. Jones' first assignment was to investigate the reasons for the crash of a Stirling bomber. But the age of high speed and hypersonic flight was just around the corner. The jet age brought stresses to aircraft skins and airframes that could scarecly have been envisaged in the era of the piston engine. In early 1944 Jones worked on the first Gloster Meteor (Britain's only operational wartime jet fighter, although it never saw combat) to crash. Later, the remnants of the V1 flying bomb and the V2 ballistic missile, came under the scrutiny of the section, as Air Defence of Great Britain - as Fighter Command had been renamed in June 1944 - sought solutions to these terrifying new weapons.

In the early 1950s, with Jones now in a senior position in accident investigation at Farnborough, his department was soon to be confronted by RAE's most serious challenge. No problem to hit British aviation was to prove more damaging than that which dogged the Comet, the world's first jet airliner, in 1953 and 1954. On May 2 1952, BOAC had inaugurated the world's first passenger jet service, with flights from London to Johannesburg. Travellers who experienced the smooth, swift and silent ride at 40 000 ft declared that they would never return to lurching through storm clouds at half that height in noisy piston-engined aircraft which took twice as long to reach their destination.

The British aircraft industry seemed to have stolen a march on America and be on the way to complete domination of the civil aviation market. Then, on May 2 1953, a year to the day after its introduction into airline service, a Comet broke up in the air during a thunderstorm over Calcutta. On that occasion the storm was blamed for the aircraft's structural failure. On January 101954, a second Comet apparently disintegrated in mid-air and disappeared into the Mediterranean Sea off the isle of Elba, 20 minutes after taking off from Rome.

Yet after this second crash, the type was put back into service after modifications. The decision was a source of deep unease to Jones, who found it incredible that service could be resumed after two such serious accidents whose cause was simply not known. "But mine was a lone voice in the wilderness among all the experts" he was subsequently to say.

It was to take a third crash, on April 8 1954, this time of a Comet flying from Cairo to Rome, before civil flights were suspended indefinitely and RAE's accident investigation team was ordered to swing into action. While one of its teams took an entire Comet fuselage and subjected it to fatigue tests in a huge water tank, Jones headed another team examining every single piece of the wreckage that had been retrieved from the bed of the Tyrrhenian Sea, north of Sicily.

This operation eventually established that the pressurised fuselages of the Comets had simply burst as they climbed to cruising height, weakened by repeated pressurisation and depressurisation. After examining the fragments, Jones's team noted that the fuselage had started to crack to crack at the corner of one of the automatic direction finder aerial cut-outs. Meanwhile, the fuselage testing team found that cracks developed at the corner of one window and rapidly spread throughout the already dangerously fatigued structure.

Such fundamental discoveries meant that the Comet had to undergo radical redesign of many of its features, a process that enabled Boeing to overtake De Havilland in design and production. By the time the new Comet 4 went into service on the transatlantic route in October 1958 the technically superior Boeing 707 was ready to capture the world market, as it did from its introduction only a month later.

Among Jones's other aircraft investigations was that of a Handley Page Victor bomber, which mysteriously disappeared on a test flight over the Irish Sea in August 1959. On that occasion it was impossible to be certain about the precise reason for the aircraft's destruction. Evidence pointed to the failure of a pitot tube, resulting in the involuntary extension of a Mach trim strut, causing a dive at more than Mach 1 into the sea.

Jones also investigated a number of non-aircraft structural disasters. Notable among these was the colapse of a box girder bridge, while under construction, at Milford haven in 1970. Jones's findings led to a rigorous reappraisal of the structure of such bridges, both in this country and abroad.

Jones was appointed OBE for his work in 1980. He retired as a principal scientific officer in the airworthiness division of the structures department at RAE in 1985. His book Air Crash:The Clues In The Wreckage was published in 1985.

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And for a bonus 10 points, what connection does Gloucestershire have with the Comet and Nimrod family...?

<{POST_SNAPBACK}>

:) Mustard, I'm sure you know something that I don't but I would have to say Dowty landing gear, Smiths instruments and possibly sonar equipment from Ultra Hydraulics or someone else in the county? Please give us your answer!

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This may be off the topic Alan, but a couple of days ago I was travelling behind a small truck, which was towing an Atlas Copco road drill generator/compressor.

This brought back memories of my days in engineering in Gloucester.

This would have only been the second or third that I have seen in OZ since getting here in '76.

As I said, this may not be transport but it certainly kept a lot of roads servicable.

Nobby

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This may be off the topic Alan, but a couple of days ago I was travelling behind a small truck, which was towing an Atlas Copco road drill generator/compressor.

This brought back memories of my days in engineering in Gloucester.

This would have only been the second or third that I have seen in OZ since getting here in '76.

As I said, this may not be transport but it certainly kept a lot of roads servicable.

Nobby

<{POST_SNAPBACK}>

Nice to hear from you Nobby - and you are certainly still on message about transport. Where would all the other wheeled vehicles - 4x4s excepted - be without roads and road builders? Come to that, would the Romans have founded Gloucster without roads? I must admit that I had not heard of the Atlas Copco however. Please tell us more. Perhaps we could have a new topic on road building!

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:huh: Dakar and Calcutta

The Comet had an excellent safety record and was much respected by the industry as a whole. But .......................

The results of all the investigations - both by the RAE and de Havilland - were presented to the Court of Inquiry, which met in the Autumn of 1954.

Hi Alan,

I somehow came across your input re-Comet when I was trawling the web for information in respect of things aeronautical.

So ,..... I have joined this group, in order to ask you if you can be of further assistance.

From your detailed and knowledgeable account of happenings involving the Comet, you may be just the man to point me in the right direction. You may even have the information which I am seeking.

I am lead to believe that the Comet was initially equipped with powered flying controls that utilised synthetic "feel", i.e the feel at the control column was dependent only upon a huge spring mechanism and not the a/c speed or the control surface deflection. Thus the load fed to the pilot was really not a lot of use as an indication of what was happening at the sharp end so to speak.

I have also been lead to believe that the early form of "Q" Feel that was eventually introduced depended upon dynamic/pitot pressure being fed into a large diameter "Q" pot, inside of which was a piston that fed loads to the conrol column. Such loads would obviously be directly proportional to the a/c speed.

I have been trying to find out how this early system actually functioned, and to date have met with no success in my quest.

Have you any ideas, or do you know of any sources of information which may be of use to me?

Thanks,

Regards,

Monty

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Greetings Monty! And welcome to the group. I hope that my Comet data has been useful. There are a few references to powered flying controls and "Q-Feel" - mainly connected with the Comet Mark 2 onwards - but I do not pretend to be a complete authority on this topic! From the extra documentary features on the DVD of the Leonardo Di Caprio film "The Aviator" I know that the idea of artificially responsive powered flying controls was developed by Howard Hughes for his Hercules flying boat, the "spruce goose" being too big for pure pilot muscle strength to operate. Nowadays of course all this sort of thing is realised by onboard computers and "fly by wire" systems. However, I do have some contacts within the Messier-Dowty organisation and will try to find out more on your behalf. Although anyone else reading this with the answer is more than welcome to make a contribution!

Hi Alan,

I somehow came across your input re-Comet when I was trawling the web for information in respect of things aeronautical.

So ,..... I have joined this group, in order to ask you if you can be of further assistance.

From your detailed and knowledgeable account of happenings involving the Comet, you may be just the man to point me in the right direction. You may even have the information which I am seeking.

I am lead to believe that the Comet was initially equipped with powered flying controls that utilised synthetic "feel", i.e the feel at the control column was dependent only upon a huge spring mechanism and not the a/c speed or the control surface deflection. Thus the load fed to the pilot was really not a lot of use as an indication of what was happening at the sharp end so to speak.

I have also been lead to believe that the early form of "Q" Feel that was eventually introduced depended upon dynamic/pitot pressure being fed into a large diameter "Q" pot, inside of which was a piston that fed loads to the conrol column. Such loads would obviously be directly proportional to the a/c speed.

I have been trying to find out how this early system actually functioned, and to date have met with no success in my quest.

Have you any ideas, or do you know of any sources of information which may be of use to me?

Thanks,

Regards,

Monty

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:) Hi Monty! I'm still working on your question but I hope that some of the following "inside information" is helpful:

I would start by saying that one mans "nicest control harmonisation" could well be another man's "bag of bolts". Achieving good handling qualities across a wide envelope is more difficult than over a narrow one. This is where modern flight control systems really start to pay dividends. By this I'm talking about flight controls where the "gains" ( known as "q") are variable depending upon whereabouts in the envelope you are and indeed what task you are undertaking. Phantom/Lightning/Harrier etc had gearing to change control response or control travel based on gear being up or down and to some extent depending on Mach number.

In fact the Harrier has a q-feel actuator installed in the nose landing gear.

But the likes of Typhoon has a variable schedule based on all of the above and in addition mass and centre of gravity (cg) location (longitude and latitude). Advances in filght simulation now allow a great deal of refinement to be done in advance of flight test, but the proof of the pudding still (thankfully) comes from flying in the real air.

Test pilot John Farley has said:-

The boffins used to say that a good starting point for harmonisation was aileron forces increasing with indicated air speed (IAS), elevator forces with IAS squared and rudder with IAS cubed. With manual controls the designer needs a bit of control design expertise to keep the forces on ailerons lighter than v squared. Typically you need to put a tab on the aileron itself which moves in the opposite direction to the surface. So aileron up tab down. This lightens the force to displace the aileron. Commonly known as a 'balance tab' or'geared tab' .There are also 'spring tabs' where the linkage driving the geared tab is 'spongy' (incorporates a spring) and can be used to further fine tune the forces left to the pilot.

The advantages of the spring tabs (which made the previously heavy ailerons on the Meteor a joy after they were fitted) is that the spring blows off a bit as speed increases so the designer can make the ailerons super light at low speed (where the spring strut acts as if it is rigid and so gives max tab deflection). At high speed the spring looses the battle and does not move the tab so far thus increasing the stick forces.

If you want to make a control heavier than v squared you again fit a tab to the trailing edge but make it work in the same direction as the surface so making it artificially heavy. Known as an 'anti-balance' tab.

If you have ordinary power controls (without fly by wire) you just have a 'q' feel device which knows the IAS and increases the artificial spring centering forces by fiddling with the position of the fixed end of the spring and hence changing the effective spring rate that the pilot is opposing.

The last paragraph is probably the most interesting. Basically the older aircraft controlled by wires / pulleys /pushrods relied on 'mass balance' (where a weight was placed forward of the pivot of the control surface) or 'balance tabs' (the surface of the control surface extended forward to counteract and balance the air pressure on the surface). When hydraulic powered controls were introduced they were so powerful (compared to mechanical system) that it was possible to move a control surface in flight without experiencing any 'feedback' or resistance pressure at the controls. Apparantly, it was possible to destroy a control surface (and the aircraft!) because the pilot could move the surface to its fullest extent using the power of the hydraulics whereas he never was possible with the old mechanical systems (or he needed large forearms / legs).

Clearly, to prevent the pilot destroying the aircraft something had to be introduced to introduce 'feedback' and a sense of pressure that would be felt if flying a mechanical control system. This could be done mechanically using the properties of springs (whereby the rate of the spring controls the pressure fed back - small deflection, small feedback pressure and then as the spring compresses the greater the force needed to compress) The springs could be located either at the flying surfaces or at the contols or anywhere in between!

More modern day aircraft use a 'Feedback Actuator' which does the same job but uses the hydraulic system to oppose itself. I know it sounds daft, but this is what happens. This can be infinitely variable and easily adjustable. Of course electro feedback actuators are used on the modern day 'fly by wire' aircraft to accomplish the same job, but that's another story...

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Hi Alan/all,

I am an Open University student doing a project on the De Havilland Comet crashes in the 1950’s. During my research I came across your piece on the 106 Comet in the Gloucestershire Transport forum. I must say that I found the piece both informative and enjoyable and was impressed by your depth of knowledge in the subject. To this end I was wondering if you can help me. I have been trawling the web for over a week now looking for information concerning the Comet disasters. What I am particularly interested in is information regarding the structural specifications i.e. fuselage material, construction methods, fuselage thickness, operating pressures etc...What I hope to do is calculate a safe fuselage thickness and whether this would have been viable. I am also looking for information regarding the fracture face characteristics of the wreckage and RAE investigation reports.

If you have any of this information or could point me in the appropriate direction I would be most grateful.

Patrick

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Hi Patrick

Thank you very much for your contribution and I am glad that my article has been helpful. I was going to suggest that you get in touch with the De Havilland Heritage Centre in north London but as they still haven't replied to one of my emails this might not be the most fruitful activity. However, I am going up to RAF Cosford tomorrow - in part to get some new photos of their Comet 1 - and will see what I can find out for you.

Best of luck with your studies in the meantime!

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Hello again Patrick ( and everyone else interested in Comets of course!)

I went up to Cosford yesterday, took some pictures ( see atttached ) and asked about the Comet ( in BOAC colours but really a French owned aircraft ) as the captions were really brief compared to many other more obscure types. The comeback from the man on the desk was try looking on the internet or watching Discovery Wings channel on satellite TV! Sorry I drew a blank but I did leave a comment card asking for more data to be emailed. Sadly there were no books or relevant multimedia in the shop either but I will keep looking on your behalf!

post-27-1142109550.jpg

post-27-1142109587.jpg

post-27-1142109626.jpg

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Hello again Patrick ( and everyone else interested in Comets of course!)

I went up to Cosford yesterday, took some pictures ( see atttached ) and asked about the Comet ( in BOAC colours but really a French owned aircraft ) as the captions were really brief compared to many other more obscure types. The comeback from the man on the desk was try looking on the internet or watching Discovery Wings channel on satellite TV! Sorry I drew a blank but I did leave a comment card asking for more data to be emailed. Sadly there were no books or relevant multimedia in the shop either but I will keep looking on your behalf!

Alan,

Sorry for not getting back earlier. Up the walls at work so had to shelf my studies for a coouple of weeks. Many thanks for looking into this for me. The photographs will be useful to me. It is for some reason comforting to know that there are Comets that survive to this day and not too far away. It would be nice if there was one in Ireland but you never know i may pay a visit to Gloucestershire and check out the comet there. I presume you are not allowed to board the comet in Cosford. What type of a Comet is it? I noticed it had round windows so presume it is not a 106 (i maybe wrong).

Here is a page you may be interested in

http://www.geocities.com/CapeCanaveral/Lab...metcr.htm#local

it contains the crash reports on Yoke Peter and Yoke Yoke. I haven't had a chance to go through them yet but they look quite informative.

Thanks again and if i come across anymore info i think you may be interested in I will let you know.

Patrick

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:) Hi Patrick! And don't worry about having to put work ahead of studies - I know all about it! Indeed, thank you for that link to the Comet site on Geocities. It is very well researched and informative and I'm sure will help your dissertation.

As for the Cosford Comet, it is an Air France Comet Mk 1A that eventually passed to the RAE with the civilian registration G-APAS and later joined the RAF as XM823. Its BOAC colours are therefore not entirely historically accurate and well spotted that it had round windows rather than the fatally weak square ones. I think the answer is that before its final flight in 1968 it was upgraded to Mk 1XB standard at some point but it remains the only preserved example that would have carried the original Ghost engines. I referred to it as a DH Type 106 mainly as I had used this in correspondence with air museums to distinguish it from the twin piston engined DH 88 Comet from the 1930s. The general visitors to Cosford sadly do not have access to the inside of G-APAS but if you got in touch with the curator a special opening might be arranged to further your investigations.

Either way, I'll keep looking for more data on this subject!

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Hi Alan,

I came across another interesting fact:

Later G-ALYP skin recovery from the Mediterranean indicated that the actual site of hull failure was at the forward emergency exit door, and not at the overhead ADF windiw frame site. The investigation was not re-opened because the failure mechansim was identical to the one cited originally, and subsequent design changes were dealing with the problem.

Did you ever come across this?

Patrick

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