de Havilland Comet

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Meet Genesis! When you travel on holiday by jet airliner, you can owe the speed and comfort (depending on the airline) to this, the de Havilland Comet, the world’s first commercial jet airliner and the start of what would become the most revolutionary age in aviation. With the invention of the jet airliner, the demographics of the world quickly changed. Speedy travel from continent to continent could now be done in a matter of hours rather than days or weeks, the once luxury privilege of travelling abroad by plane would soon be handed to the masses, and it would destroy the tourist industry of many domestic holiday resorts such as Skegness and Blackpool. But the Comet, the leader of the pack, would soon become the biggest victim, as the cutting edge was the one to find all the problems, and would become the beginning of the end for Britain’s aviation industry.

Considerations for the Comet went back to before the end of World War II in 1943. While plans were being made for Britain’s first jet fighter to combat the Luftwaffe, there were also ideas for a new and revolutionary airliner to be built upon the war’s conclusion. With developments in presusrisation and increased range being placed onto contemporary high-altitude bombers such as the B-17 Flying Fortress and the Avro Lancaster, designers were eager to incorporate these into the their new airliner, which, at the time, was a proposed transatlantic mail carrying plane that would travel at

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An early shot of the 1949 prototype Comet in-flight over England.

400mph and could carry 1 ton of mail between London and New York. The contract for building such an aircraft was given to De Havilland founder Sir Geoffrey de Havilland, whose personal influence and expertise was used to champion the development of a jet propelled aircraft; and proposed a specification for a pure turbojet-powered design, dubbed the Type IV.

The Type IV was quickly renamed into the De Havilland Type 106, and by 1944 a small framed aircraft had been drawn up. Various demands for increased size and performance quickly meant that the design had to evolve. Following the end of World War II, British national carrier Imperial Airways merged with British Airways (not related to the current airline) to form BOAC, British Overseas Airways Corporation. BOAC desired to start their new career and enter their brave new world with a world beating aircraft, and became involved with the Type 106 project, requesting that the 1946 design, which consisted of 24-seats, be increased in size to 36-seats. By 1947, the Comet had almost completely taken shape to its final design, a long smooth body with an angled rudder and powered by four Rolls Royce Avon engines mounted within the wings next to the fuselage. The aircraft was christened the name Comet in December 1947, by which time BOAC had ordered 14 for delivery by 1952.

In order to achieve perfect, the Comet had to be tested to destruction. From 1947 to 1948, de Havilland conducted an extensive research and development phase, including the use of several stress test rigs at their Hatfield factory for small components and large assemblies alike. Sections of pressurised fuselage were subjected to high-altitude flight conditions via a large decompression chamber on-site, and tested to failure. However, tracing fuselage failure points proved difficult with this method, and de Havilland ultimately switched to conducting structural tests with a water tank that could be safely configured to increase pressures gradually. The entire forward fuselage section was tested for metal fatigue by repeatedly pressurising to 2.75 pounds per square inch overpressure and depressurising through more than 16,000 cycles, equivalent to about 40,000 hours of airline service. The windows were also tested under a pressure of 12 psi, 4.75 psi above expected pressures at the normal service ceiling of 36,000ft. One window frame survived 100 psi, about 1,250% over the maximum pressure it was expected to

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A BOAC Comet is seen at Heathrow in 1953, demonstrating the original square window design.

encounter in service.

The first DH 106 Comet Prototype, G-5-1, was completed in 1949, and after several ground tests, the first production jet airliner took to the skies on July 27th of the same year, flying for 31 minutes. Registered G-ALVG, the aircraft made a spectacular public performance at the 1949 Farnborough Airshow prior to the start of flight trials. A year later, the second prototype G-5-2 made its maiden flight. The second prototype was registered G-ALZK in July 1950 and it was used by the BOAC Comet Unit at Hurn from April 1951 to carry out 500 flying hours of crew training and route proving. Australian airline Qantas also sent its own technical experts to observe the performance of the prototypes, seeking to quell internal uncertainty about its prospective Comet purchase. Both prototypes could be externally distinguished from later Comets by the large single-wheeled main landing gear, which was replaced on production models starting with G-ALYP by four-wheeled bogies.

For ease of training and fleet conversion, de Havilland designed the Comet’s flight deck layout with a degree of similarity to the Lockheed Constellation, an aircraft that was popular at the time with key customers such as BOAC. The cockpit included full dual-controls for the captain and first officer, while a flight engineer controlled various key systems, including fuel, air conditioning, and electrical systems. The navigator occupied a dedicated station with a table across from the flight engineer. Several of the Comet’s avionics systems were new to civil aviation. One such feature was irreversible powered flight controls, which increased the pilot’s ease of control and the safety of the aircraft by preventing aerodynamic forces from changing the directed positions and placement of the aircraft’s control surfaces. Additionally, a large number of the control surfaces, such as the elevators, were equipped with a complex gearing system as a safeguard against accidentally over-stressing the surfaces or airframe at higher speed ranges.

Though the Comet prototype was powered by Rolls Royce Avon engines found in the English Electric Canberra bombers, De Havilland chose in-house designs for the production models, these being the De Havilland Ghost gas turbine engine turbojet engines, distinguishable from Rolls Royce models by the smaller engine intakes. Engines were mounted within the plane’s wing so as to reduce the drag of pod-mounted engines. These engines provided 20,000lbf of thrust, whisking the Comet to a 460mph cruising speed, an operational ceiling of 42,000ft, and a range of 1,500 miles.

On January 22nd, 1952, after heavy proving tests, the fifth production aircraft, G-ALYS, received the first Certificate of Airworthiness awarded to a Comet, six months ahead of schedule. This was followed in May of the same year by proving flights by BOAC, flying from Heathrow to Johannesburg as the first scheduled jet airliner service with fare paying passengers. The final Comet from BOAC’s initial order, registered G-ALYZ, began flying in September 1952 and carried cargo along South American routes while simulating passenger schedules. The Comet was a hit with passengers including Queen Elizabeth, the Queen Mother and Princess Margaret, who were guests on a special flight on June 30th, 1953, hosted by Sir Geoffrey and Lady de Havilland, and thus became the first members of the British Royal Family to fly by jet.

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A UAT Comet 1 on the ground during the early 1950’s, again showing the original square window design.

Flying by Comet was 50% faster than even the most advanced Piston-engined aircraft, the Douglas DC-6, being on average 180mph faster and having a faster rate of climb. In August 1953 BOAC scheduled nine-stop London to Tokyo flights by Comet for 36 hours, compared to 86 hours and 35 minutes on their Argonaut piston airliner. The five-stop flight from London to Johannesburg was scheduled for 21 hr 20 min.

In terms of design, the Comet was actually quite a small aircraft, being only the size of a later Boeing 737-100, and only able to carry half its capacity. This didn’t bother designers at the time, as travelling by air was similar to the Victorian ideal of travelling first class by steamship, with luxury service and interiors for the top members of British society. Seats were reclining, known as ‘Slumberseats’, on-board catering was second-to-none, with white-jacket waiter service at your seat. Essentially, early jet travel was the equivalent of a business jet you had to share with other rich fogies. BOAC also lauded the fact that the Comet was infinitely more quiet internally than piston-powered propeller planes, and had no vibrations due to the lack of moving parts.

As mentioned, the Comet’s pioneering speed and comfort meant that it would quickly give rise to foreign tourism, something that previously had not been easily possible. With following successful jet airliners, and the later offering of low-cost carriers spearheaded by Laker Airways and Virgin Atlantic, meant that travelling abroad was no longer a distinction for the extremely wealthy, but for anyone who wanted to take a trip to an exotic location. In my life I’ve travelled to New York 9 times, every one of which I owe to the technology mastered by the Comet. However, such innovation came at the price of the UK tourist industry, which, with our cold, unpleasant and unpredictable climate, meant that potential visitors to British resorts such as Blackpool, Skegness and Southend now had the option to go to places such as the Canary Islands, Florida, Dubai and other modern megaresorts. As such, financially this has sucked many UK towns and cities dry, though some have seen a revival in recent years thanks more to nostalgia and being made incredibly cheap.

However, before the Comet was even a year old, this cutting edge piece of technology began to suffer losses, and that’s even before we got to the biggest problems of them all. On October 26th, 1952, the Comet suffered its first hull loss when a BOAC flight departing Rome’s Ciampino airport failed to become airborne and ran into rough ground at the end of the runway, injuring two passengers and writing off the aircraft. A year

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A Comet undergoes pressurisation tests inside a giant water tank following multiple fatal crashes of the type. Water was drained and refilled to simulate the effects of pressurisation and depressurisation.

later on March 3rd, 1953, a new Canadian Pacific Airlines Comet 1A, registered CF-CUN and named Empress of Hawaii, failed to become airborne while attempting a night takeoff from Karachi, Pakistan, on a delivery flight to Australia. The aircraft plunged into a dry drainage canal and collided with an embankment, killing all five crew and six passengers on board. The accident was the first fatal jetliner crash, as well as the Comet’s first accident to result in fatalities. In response, Canadian Pacific cancelled its remaining order for a second Comet 1A and never operated the type in commercial service.

The Comet’s second fatal accident occurred on May 2nd, 1953, when BOAC Flight 783, a Comet 1, registered G-ALYV, crashed in a severe thundersquall six minutes after taking off from Calcutta-Dum Dum (now Netaji Subhash Chandra Bose International Airport), India, killing all 43 on board. Witnesses observed the wingless Comet on fire plunging into the village of Jagalgori, leading investigators to suspect structural failure. The inquiry concluded that the aircraft had encountered extreme negative G forces during takeoff; severe turbulence generated by adverse weather was determined to have induced down-loading, leading to the loss of the wings.

However, while these early crashes had been largely associated with Pilot Error, the worst for the Comet had yet to come, and it would spell the end for this pioneering aircraft’s days in the sunlight of success. On January 10th, 1954, 20 minutes after taking off from Ciampino, the first production Comet, G-ALYP, broke up in mid-air while operating BOAC Flight 781 and crashed into the Mediterranean off the Italian island of Elba with the loss of all 35 on board. On April 8th the same year, South African Airways Flight 201, operated by hired BOAC Comet G-ALYY, broke up after departure from Rome, killing all 21 aboard. In both instances, a lack of witnesses and only partial radio communication with the aircraft meant that investigation of these crashes was made difficult.

Almost immediately however, word had spread to the Press regarding these tragic accidents, and speculations of sabotage by rival manufacturers such as Boeing and Douglas began to spread. To investigate the crashes, the Abell Committee was formed by the British Government, and focused on six potential aerodynamic and mechanical causes: control flutter (which had led to the loss of DH 108 prototypes), structural failure due to high loads or metal fatigue of the wing structure, failure of the powered flight controls, failure of the window panels leading to explosive decompression, or fire and other engine problems. The committee concluded that fire was the most likely cause of the problem, and a number of changes were made to the aircraft to protect the engines and wings from damage that might lead to another fire. This was followed later the same year by the Cohen Committee, which superseded the investigation into the crashes.

With the recovery of large sections of G-ALYP from the Elba crash and BOAC’s donation of an identical airframe, G-ALYU, for further examination, an extensive “water torture” test eventually provided conclusive results. This time, the entire fuselage was tested in a dedicated water tank that was built specifically at Farnborough to accommodate its full length. Stress around the window corners was found to be much higher than expected and stresses on the skin were generally more than previously expected or tested. This was due to stress concentration, a consequence of the windows’ square shape, which generated levels of stress two or three times greater than across the rest of the fuselage.

In water tank testing, engineers subjected G-ALYU to repeated re-pressurisation and over-pressurisation, and on June 24th, 1954, after 3,057 flight cycles (1,221 actual and

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A Comet 4 working for BEA, demonstrating the later oval window design.

1,836 simulated), G-ALYU burst open, being ripped apart at a corner of the forward left escape hatch cutout. A further test reproduced the same results. Based on these findings, Comet 1 structural failures could be expected at anywhere from 1,000 to 9,000 cycles. Before the Elba accident, G-ALYP had made 1,290 pressurised flights, while G-ALYY had made 900 pressurised flights before crashing. Dr P.B. Walker, Head of the Structures Department at the RAE, said he was not surprised by this, noting that the difference was about three to one, and previous experience with metal fatigue suggested a total range of nine to one between experiment and outcome in the field could result in failure.

With the discovery of the structural problems of the early series, all remaining Comets were withdrawn from service, while de Havilland launched a major effort to build a new version that would be both larger and stronger. All outstanding orders for the Comet 2 were cancelled by airline customers. The square windows of the Comet 1 were replaced by the oval versions used on the Comet 2, which first flew in 1953, and the skin sheeting was thickened slightly. Remaining Comet 1s and 1As were either scrapped or modified with oval windows and rip-stop doublers.

However, by the time the Comet eventually returned to the air, it was too late to save either itself or its reputation. As British investigators worked on discovering the cause of the Comet crash, waiting eagerly with baited breath were Boeing and Douglas, who, at the time, were planning competitive aircraft, the Boeing 707 and the Douglas DC-8. After discovery of metal fatigue due to square windows, Boeing and Douglas redesigned their aircraft to incorporate the stronger oval windows, and before Comet flights resumed in 1958, Boeing burst onto the scene with the 707, followed by the DC-8 in 1960. Immediately, the 707 was lauded for its design, performance, stylistic beauty and reliability, and before long pretty much every major airline in the world would have at least one on their books, including Comet launch customer BOAC.

Though the Comet had been extensively redesigned with the later Comet 3 and Comet 4 variants, which extended the body, improved the range and increased capacity, it was too late to save the reputation of the ailing aircraft, and both the credibility of the Comet

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Dan-Air were among the last operators of the Comet, using them on European charter flights into the 1980’s.

and the British Aviation Industry in general had been compromised. Many airlines cited the failure of the Comet as a British fault, and thus were sceptical to buy later British aircraft such as the Trident and VC10. In 1965, BOAC retired its last Comets from service after only 13 years, and while the aircraft would go on to be popular among airlines in Asia and Africa, including ex-BOAC aircraft being used by charter airlines such as Dan-Air, only 114 (including prototypes) were ever built, a fraction of the 1,010 Boeing 707’s and 556 Douglas DC-8’s that continued to be built long after Comet production ended in 1964.

Comets remained in commercial passenger service with a variety of large, mostly non-European, airlines into the 1970’s, including carriers such as Malaysia-Singapore Airlines (MSA), East African Airways, British European Airways, Dan-Air London, Kuwait Airways, Middle East Airlines, Misrair, Mexicana and South African Airways. Eventually, by the end of the decade, all airworthy Comets belonged to Dan-Air, and were operated on internal European flights until they were retired from commercial service in 1981 without ceremony. While a few were preserved, several saw later service with the Royal Air Force, largely as trainers for crews flying with the Hawker Siddeley Nimrod, a maritime patrol aircraft that was built from converted ex-BOAC Comets from 1967. RAF Comets were also used as VIP transports and given other useful tasks before the last airworthy Comet, Comet 4C serial XS235, named Canopus, was retired on March 14th, 1997, bringing an end to the pioneer Jet Airliner.

In all, 11 Comets, three Comet 1’s (including the sole surviving square-windowed

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RAF owned Comet 4C “Canopus” was the last airworthy Comet, being retired in 1997.

example), one Comet 2 and 7 Comet 4’s are preserved in varying conditions. While XS235 is kept in a taxiable condition, plans are in progress to possibly return this aircraft to the skies for airshows, though there is difficulty in gaining a license to do so, especially after the Shoreham Airshow crash of 2015.

Today, the Comet is regarded as both one of the greatest successes and most monumental failures of aviation history. While the aircraft was, at the time, arguably the most revolutionary aircraft since the Wright Flyer, and spent its early days being lauded for being the pinnacle of style, luxury and performance, it’s subsequent crashes have tarnished its once gleaming reputation. Today, most aviation enthusiasts will look back on the Comet with mixed opinions. However, one must not blame the Comet for everything as it was a very adventurous leap for mankind at the time. In an age when trains were still powered by steam, the idea of a jet airliner was something utterly audacious and extreme by every definition of the word. But cutting edge came at a price, and it was unfortunately the Comet that had to bear the brunt of entering into a new world of discovery. If the roles had been reversed, and the Boeing 707 had been in the Comet’s shoes, and the Comet profited off the 707’s many crashes, then perhaps the UK aviation industry would still be alive and kicking today.

But as is, the UK paved the way with the Comet and ultimately suffered the blows being a pioneer have to offer. The Comet is sadly now gone, but its legacy remains to this day in all jet airliners that continue to arrive and depart the airports of the world, the Boeing 747’s, Airbus A380’s and so forth of today’s aviation industry can all owe their construction to that plucky Silver Bird that rocketed away from Hatfield in 1949 and would alter the face of society almost overnight.