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De Havilland Comet

DH 106 Comet

Picture - Comet 3 G-ANLO in BOAC markings at Farnborough in September 1954

Role: Airliner
Manufacturer: de Havilland
First flight: 27 July 1949
Introduced: 2 May 1952 with BOAC
Retired: 14 March 1997 (Comet 4C XS235)
Status: Retired
Primaryusers: BOAC Royal Air Force Dan-Air Aerolx­neas Argentinas; See Operators
Number built: 114 (including prototypes)
Unit cost: £250,000 in 1952
Variants: Hawker Siddeley Nimrod

The de Havilland DH 106 Comet was the world's first commercial jet airliner to reach production. Developed and manufactured by de Havilland, it first flew in 1949 and was a landmark in aeronautical design. It featured an extremely aerodynamically clean design with its four de Havilland Ghost turbojet engines buried into the wings, a low-noise pressurised cabin, and large windows; for the era, it was an exceptionally comfortable design for passengers and showed signs of being a major success in the first year upon launching.

However, a few short years after introduction into commercial service, the Comet suffered from catastrophic metal fatigue, which in combination with the pressurisation, caused two well-publicised accidents where the aircraft tore apart in mid-flight. The Comet had to be withdrawn and extensively tested to discover the cause; the first incident had being incorrectly identified as having been caused by an onboard fire. Several contributory factors, such as window installation methodology, were also identified as exacerbating the problem. The Comet was extensively redesigned to eliminate this design flaw. Rival manufacturers meanwhile developed their own aircraft and heeded the lessons learnt from the Comet.

Although sales never fully recovered, the redesigned Comet 4 series subsequently enjoyed a long and productive career of over 30years. The Comet was adapted for a variety of military roles, such as surveillance, VIP, medical and passenger transport; the most extensive modification resulted in a specialised maritime patrol aircraft variant, the Hawker Siddeley Nimrod. Nimrods are still in service with the RAF and are expected to be retired in March 2011, over 60 years after the Comet's first flight.

Development

During the Second World War, the Brabazon Committee was formed on 11 March 1943 to determine Britain's postwar airliner needs. One of the recommendations set a design "target" of a pressurised, transatlantic mailplane that could carry a ton of payload at a cruising speed of 400 mph. Challenging the widely-held scepticism of jet engines as too fuel-hungry and unreliable, committee member Sir Geoffrey de Havilland, head of the de Havilland company, used his influence and the company's expertise with jets to specify a turbojet-powered design. The committee accepted the proposal, calling it the "Type IV" (of five designs), and awarded the production contract to de Havilland's Type 106. The first-phase designs focused on short and intermediate range mailplanes with a small passenger compartment and as few as six seats, later redefined as a long-range airliner with 24-seat capacity. Out of all the Brabazon designs, the DH 106 was seen as the riskiest. Nevertheless, British Overseas Airways Corporation (BOAC) found the Type IV's specifications attractive, initially proposing a purchase of 25 aircraft and, in December 1945, when a "firm contract" was laid out, revising the number to 10.

A design team was formed in 1946 under the leadership of Chief Designer Ronald Bishop, who had been responsible for the Mosquito fighter-bomber. A number of unorthodox configurations were considered, all of which were subsequently rejected. The Ministry of Supply was interested in the most radical of the proposed designs and issued Operational Requirement OR207 to Specification E.18/45 for two experimental DH 108s ordered as "proof-of-concept" aircraft to test swept-wing configurations in both low speed and high speed flight.

Picture - Design studies for the DH 106 Comet 1944-1947 (Artist's impression)

Even before the DH 108s were completed, further requests from BOAC necessitated a redesign of the DH 106 from the original four-engined (Halford H.1 Goblin-powered) 24-seat airliner to a larger 36-seat version to specification 22/46 in September 1946. With no time to develop the technology required for the tailless configuration, Bishop opted for a more conventional 20Ëšswept-wing design with unswept tail surfaces, married to an enlarged fuselage accommodating 36 passengers, arranged four abreast with a central aisle. Four new, more powerful Rolls-Royce Avons were to be incorporated in pairs buried in the wing roots, but Halford H.2 Ghost engines were eventually specified as an interim solution while the Avons cleared certification. The redesigned DH 106 was named the DH 106 Comet in December 1947. First revised orders for both BOAC and British South American Airways for a combined total of 14 aircraft had a projected delivery schedule set for 1952.

During 1947-1948, de Havilland undertook an extensive research and development phase, utilizing a number of stress test rigs at Hatfield for small components and large assemblies. Sections of the pressurised fuselage were subjected to the conditions of a flight at altitude in the company's decompression chamber. The DH 108s were also modified to test the DH 106's power controls.

The first flight of the first prototype DH 106 Comet (carrying Class B markings G-5-1) took place on 27 July 1949 from Hatfield, and lasted 31minutes. The pilot was de Havilland Chief Test Pilot John Cunningham, a famous wartime night-fighter pilot, who later commented, "I assumed that it would change aviation, and so it has proved. It was a bit like Concorde." Also on board were co-pilot Harold "Tubby" Waters, engineers John Wilson (electrics) and Frank Reynolds (hydraulics), along with flight test observer Tony Fairbrother. Fairbrother commented, "The world changed as our wheels left the ground."

G-5-1 was publicly displayed at the 1949 Farnborough Airshow before beginning flight trials. A year later, the second prototype made its maiden flight. On 2 April 1951, this aircraft was delivered to the BOAC Comet Unit at Hurn under the registration G-ALZK and carried out 500 flying hours of crew training and route proving.Both prototypes were distinguished by large main wheel units that were replaced by four-wheeled bogies on each main leg for the subsequent production series.

The British Government considered the development of the Comet a highly ideological matter, as high-ranking officials perceived the need to meet foreign competition and surpass them when there was the opportunity to do so:

-Duncan Sandys, Minister of Supply, 1952.

Picture - Comet interior, National Museum of Flight, East Fortune

Design

The Comet is an all-metal low-wing cantilever monoplane powered by four jet engines, approximately the length of a Boeing 737, carrying fewer people in a significantly more spacious environment. The earliest Comets had 11 rows of seats with four seats to a row in the 1A configuration used by Air France; BOAC used an even roomier arrangement of 36 seats. The Comet's four-place cockpit held two pilots, a flight engineer, and a navigator. The cabin was quieter than those of propeller-driven airliners. Amenities included a galley that could serve hot and cold food and drinks, a bar, and separate men's and women's washrooms. For emergencies, life rafts were stored in the wings near the engines and life vests were stowed under each seat bottom.

Picture - DeHavilland Comet 4 flight deck

The clean, low-drag design featured many unique or innovative design elements, including a swept wing leading edge, integral wing fuel tanks, and four-wheel bogie main undercarriage units designed by de Havilland. Two pairs of de Havilland Ghost 50 Mk1 turbojet engines were buried in the wings close to the fuselage. Chief Designer Bishop chose this configuration because it avoided the drag of podded engines and allowed a smaller fin and rudder, since the hazards of asymmetric thrust were reduced. The engines' higher mounting in the wings also reduced the risk of ingestion damage, a major problem for turbine engines. These benefits were compromised by increased structural weight and general complexity, including armour for the engine cells (in case of an engine explosion) and a more complicated wing structure. This arrangement also carried higher risk of catastrophic wing failure in case of an engine fire, cited as the main reason the Boeing Aircraft Company chose podded engines in their subsequent jet bomber and airliner designs.

Picture - The air intakes of preserved Comet 4C at Imperial War Museum Duxford.

The Comet was originally intended to have two hydrogen peroxide-powered de Havilland Sprite booster rockets for takeoff under hot and high conditions from airports such as Khartoum and Nairobi. These were tested on 30 flights, but the Ghosts were considered powerful enough without them, although Sprite fittings were kept on production aircraft. The later Comet 4 was highly rated for its takeoff performance from high altitude locations such as Mexico City. Newer and more powerful AJ.65 Avon engines replaced the Ghosts on the Comet 2. High engine performance combined with a low weight (compared to the Boeing 707 and Douglas DC-8), and exceptionally clean design all contributed to its high performance. Early-model Comets had the advantage of requiring low maintenance, the de Havilland Ghost engines being a key contributing factor. Mounting the engines in a low-wing position combined with numerous service panels allowed for "easy" and efficient maintenance.

Picture - Comet 4C landing gear

The Comet's thin metal skin was composed of advanced new alloys (Directorate of Technical Development 564/L.73 and DTD 746C/L90) and was both chemically bonded using the adhesive Redux and riveted, which saved weight and reduced the risk of fatigue cracks spreading from the rivets. When it went into service with BOAC on 2 May 1952, the Comet was the most exhaustively tested airliner in history. After the Comet entered production, for safety reasons, and to limit the damage to the specimens, a water tank was used instead of the decompression chamber. The entire forward fuselage section was tested for metal fatigue by repeatedly pressurising to 2.75psi overpressure (11psi = 76kPa) and depressurising through more than 16,000 cycles, equivalent to about 40,000hours of airline service. The windows were tested under a pressure of 12psi (83kPa), 4.75psi above the normal service ceiling of 36,000ft (10,973m). One window frame survived a massive 100psi (690kPa), about 1,250% over the maximum pressure it would encounter in service.

In 1953, Sud-Est's design bureau, while working on the Sud Aviation Caravelle, licensed several design features from de Havilland, a company Sud had previously collaborated with on earlier licenced designs, including the DH 100 Vampire. The entire nose and cockpit layout from the Comet 1 was grafted onto the Caravelle.

Operational history

Introduction

The first production aircraft (G-ALYP) flew on 9 January 1951 and subsequently was on loan to BOAC for development flying by the Comet Unit. On 22 January 1952, G-ALYS was the first Comet to receive a Certificate of Airworthiness, six months ahead of schedule. As part of the BOAC route proving trials, on 2 May, G-ALYP took off on the world's first "jetliner" flight with fare-paying passengers, beginning scheduled service to Johannesburg. The last Comet from the initial order (G-ALYZ) began flying in September 1952, carrying 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 30 June 1953 hosted by Sir Geoffrey and Lady de Havilland, and thus became the first members of the British Royal Family to fly by jet. A total of 30,000 passengers was carried during the first year of service. For the travelling public, the Comet offered flights about 50% faster than advanced piston-engined types such as the Douglas DC-6 (490mph for the Comet compared to 315mph for the DC-6B), and its rate of climb was also far higher, which could cut flight times in half. The passenger experience was relatively unique compared to the contemporary piston-engined airliner. The Comet cabin was roomy, with the BOAC-designed "slumberseat", a comfortable, reclining design, allowing for greater leg room, both in front and behind. The large "picture window" view and accommodations for a table setting for a row of passengers afforded a "feel of comfort and luxury" atypical of most airliners of the period. One of the most striking aspects of flight on the Comet was the quiet, "vibration-free flying" touted by BOAC.

Commercial success was widely expected, with a profitable passenger load factor as low as 43%. The Ghost engine was smooth, relatively simple, fuel-efficient above 30,000ft (9,144m), had low maintenance costs, and enabled operations above weather the competition had to fly through. At the height of Comet's early flying career, the BOAC Comet 1 fleet flew routes such as London-Singapore, London-Tokyo, and London-Johannesburg several times a week.

Early accidents and incidents

Picture - DH106 Comet 1 preserved in the colours of BOAC G-APAS, this aircraft also served with the RAF as XM823, now at RAF Cosford

On 26 October 1952, a BOAC flight departing from Ciampino airport near Rome failed to become airborne and ran into rough ground at the end of the runway. Two passengers sustained only minor injuries, but the aircraft was a total loss. The following March, a new Canadian Pacific Airlines Comet 1A (CF-CUN), known as "Empress of Hawaii," being delivered to Australia, also failed to become airborne on takeoff from Karachi, Pakistan. The aircraft plunged into a dry drainage canal and collided with an embankment, killing all five crew and six passengers on board, the first fatal crash of a passenger jet airliner.

Both of these accidents were originally attributed to pilot error as over-rotation had led to a loss of lift from the leading edge of the aircraft's wing. It was later determined the wing profile led to a loss of lift at high angle of attack, and the engine inlets suffered from a lack of pressure recovery in these conditions as well. The wing leading edge was re-profiled with a pronounced "droop", and a wing fence was added to control spanwise flow. A fictionalised investigation into these takeoff accidents was the subject of the 1959 novel, Cone of Silence by Arthur David Beaty, a former BOAC captain. Cone of Silence was made into a film in 1960, and Beaty also recounted the story of the Comet's takeoff accidents in a chapter of his 1984 non-fiction work, Strange Encounters: Mysteries of the Air.

The next fatal accident involving passengers was on 2 May 1953, when a BOAC Comet 1 (G-ALYV) crashed in a severe tropical storm six minutes after taking off from Calcutta/Dum Dum (now Netaji Subhash Chandra Bose International Airport), India, killing all 43 on board. The crash was attributed to structural failure of the airframe with witnesses observing the wingless Comet on fire plunging into the Indian Ocean.

India Court of Inquiry

A court of inquiry was convened by the Central Government of India to examine the cause of the accident. The conclusions of the inquiry focused on the extreme negative G forces encountered in the thundersquall. A large proportion of the aircraft was recovered and reassembled at Farnborough. The break-up was found to have began with a left hand elevator spar failure in the stabiliser. The immediate focus was on the severe turbulence encountered that induced down-loading which subsequently precipitated the loss of the wings. Examination of the cockpit controls led to a belief that the pilot may have inadvertently overstressed the aircaft when pulling out of a steep dive by over-manipulation of the fully powered flight controls.

Recommendations from the court revolved around the enforcement of stricter "rough air" speed limits. The tragedy led to two significant developments: all Comets were equipped with "weather radar" and the introduction of "Q feel", a system that ensured that control column forces (invariably called "stick forces") would be proportional to control loads. The artificial feel was the first of its kind to be introduced in any aircraft. The Comet 1 and 1A had been criticised for a lack of "feel" in their controls, although test pilot John Cunningham contended, "it flew extremely smoothly and responded to the controls in the best way de Havilland aircraft usually did".

Picture - DH.106 Comet 1 of BOAC at London Heathrow on 2 June 1953.

Comet disasters of 1954

Rome's Ciampino airport, the site of the first Comet hull loss, was again the origin of more disastrous Comet flights just over a year later. On 10 January 1954, 20minutes after taking off from Ciampino, Comet G-ALYP ("Yoke Peter"), BOAC Flight 781, broke up in flight and crashed into the Mediterranean off the Italian island of Elba, with the loss of all 35 on board. With no witnesses to the disaster and only "sketchy" and incomplete radio transmissions left behind, there appeared to be no obvious reason for the crash. Engineers at de Havilland immediately recommended 60 modifications aimed at any possible design flaw while the Abell Committee met to determine potential causes of the crash.

Abell Committee Court of Inquiry

Media attention centred upon sabotage; other speculation ranged from "clear-sky" turbulence to an explosion of vapour in an empty fuel tank. The committee soon focused on six potential aerodynamic and mechanical causes: control flutter (which had led to the loss of the de Havilland DH 108 Swallow 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 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 which might lead to another fire.

"The cost of solving the Comet mystery must be reckoned neither in money nor in manpower."

During this investigation, the Royal Navy conducted recovery operations. The first wreckage was discovered on 12 January and the search continued until August, by which time, 70% of the main structure, 80% of the power section and 50% of the aircraft systems/equipment had been recovered. The forensic reconstruction effort was only lately underway when the Abell Committee reported their findings. On 4 April, Lord Brabazon wrote to the Minister of Transport, "Although no definite reason for the accident has been established, modifications are being embodied to cover every possibility that imagination has suggested as a likely cause of the disaster. When these modifications are completed and have been satisfactorily flight tested, the Board sees no reason why passenger services should not be resumed." Comet flights resumed on 23 March 1954.

On 8 April 1954, Comet G-ALYY ("Yoke Yoke"), on charter to South African Airways, was on a leg from Rome to Cairo (of a longer flight from London to Johannesburg), when it crashed in the waters near Naples. The fleet was immediately grounded once again and a large investigation board was formed under the direction of the Royal Aircraft Establishment (RAE). Prime Minister Winston Churchill tasked the Royal Navy with helping locate and retrieve the wreckage so that the cause of the accident could be found. The type's Certificate of Airworthiness was revoked and line production suspended at Hatfield while the BOAC fleet was grounded.

Cohen Committee Court of Inquiry

On 19 October 1954, a court of inquiry was set up under the chairmanship of Lord Cohen to examine the causes of the Comet crashes. Investigators under the leadership of Sir Arnold Hall, Director of the RAE at Farnborough, began considering fatigue as the most likely cause of both accidents and initiated further research into measurable strain on the skin. With the recovery of large sections of G-AYLP from the Elba crash and G-ALYU, an extensive "water torture" test eventually provided conclusive results. 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, the levels of stress at these corners could be two or three times that across the rest of the fuselage.

Before the Elba accident, G-ALYP had made 1,290 pressurised flights and at the time of the Naples accident, G-ALYY had made 900 pressurised flights. Dr. P.B. Walker, Head of the Structures Department (RAE) said he was not surprised by this, noting that the difference was about 3 to 1 and previous experience with metal fatigue suggested a total range of 9 to 1 between experiment and outcome in the field could result in failure. Thus, if the tank test result was "typical", aircraft failures could be expected at anywhere from 1,000 to 9,000 cycles. Engineers subjected an identical airframe, G-ALYU, to repeated re-pressurisation and over-pressurisation, and on 24 June 1954, after 3,057 flight cycles (1,221 actual and 1,836 simulated), G-ALYU burst open. Hall, Geoffrey de Havilland and Bishop were immediately called to the scene, where the water tank was drained to reveal the fuselage had ripped open at a corner of the forward port-side escape hatch cutout. A further test reproduced the same results. By then, the RAE had reconstructed about â…” of G-ALYP at Farnborough and found fatigue crack growth from a rivet hole at the low-drag fiberglass forward "window" around the Automatic Direction Finder, had caused a catastrophic breakup of the aircraft in high altitude flight.

The rivet problem was exacerbated by the punch rivet construction technique employed. The windows had been engineered to be glued and riveted, but had been punch riveted only. Unlike drill riveting, the imperfect nature of the hole created by punch riveting may cause the start of fatigue cracks around the rivet. Hall, the principal investigator, concluded, "In the light of known properties of the aluminium alloy D.T.D. 546 or 746 of which the skin was made and in accordance with the advice I received from my Assessors, I accept the conclusion of RAE that this is a sufficient explanation of the failure of the cabin skin of Yoke Uncle by fatigue after a small number, namely, 3,060 cycles of pressurisation."

The "Cohen Court" closed on 24 November 1954. Although the court "found that the basic design of the Comet was sound", nonetheless, de Havilland began a refit programme that involved strengthening the fuselage and wing structure, employing thicker gauge skin and replacing all square windows and panels with rounded ones.

As is often the case in aeronautical engineering, other aircraft manufacturers learned from, and profited by, de Havilland's hard-learned lessons. Although the Comet had been subjected to the most rigourous testing of any contemporary airliner, the "dynamic stresses" of pressurisation were not well known, and the "Comet had pushed 'the state-of-the-art' beyond its limits." According to John Cunningham, representatives from American manufacturers such as Boeing and Douglas, (privately) "admitted that if it hadn't been for our problems, it would have happened to one of them".

Resumption of service

Picture - Dan-Air London Comet 4 G-APDB preserved at Duxford, July 1985

The Comet did not resume commercial airline service until 1958. Following the structural problems of the early series, all remaining Comets were withdrawn from service, with de Havilland launching a major effort to build a new version that would be both larger and stronger. 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. The remaining Comet 1s and 1As were either scrapped or modified with oval window rip-stop doublers (a thick, structurally strong ring of material that prevents a crack from spreading further), but a program to produce a Comet 2 with more powerful Avons was delayed. All production Comet 2s were modified to alleviate the fatigue problems and most of these served with the RAF as the Comet C2. Development flying and route proving with the Comet 3 allowed BOAC to accelerate the certification of what was destined to be the most successful variant of the type. On 24 September 1958, the Comet 4 received a Certificate of Air Worthiness and, the next day, BOAC took delivery of its first two Comet 4s.

The Comet 4 enabled BOAC to inaugurate the first regular jet-powered transatlantic services to begin that same year, albeit the North Atlantic crossing still required a fuel stopover at Gander. Despite the publicity garnered by being the first across the Atlantic with the London-New York crossing on 4 October 1958, by the end of the month, Pan Am was flying the Boeing 707 along the same route and, by the end of the year, the Douglas DC-8 would be ready for service. Both of the American jets were larger, faster, longer-ranged, and more cost-effective to operate than the Comet. In analysing the route structure the Comet could fly effectively, BOAC reluctantly cast about for a successor and, by 1958, had entered into an agreement with Boeing to purchase the 707.

In 1959, BOAC began shifting its Comet operations from the Atlantic run gradually to other routes and releasing the Comet to the associate companies, the moves resulting in the Comet 4's ascendancy as a premier airliner being relatively brief. Besides the 707/DC-8 duo, the imminent introduction of the Vickers VC10 meant the Comet's competitors assumed more of the role initially pioneered by the Comet, that of high-speed, long-range passenger service. Orders from other air carriers were gradually falling off in the 1960s with a total of 76 of the Comet 4 family delivered from 1958 to 1964. BOAC retired its Comet 4s from revenue service in 1965 but other operators continued flying Comets in commercial passenger service until 1981. Dan-Air played a significant role in the fleet's later history and, at one time, owned all 48 remaining airworthy civil Comets. On 14 March 1997, a Comet 4C (XS235) which had been acquired by the British Ministry of Technology and used for radio, radar and avionics trials, made the last documented Comet flight.

Picture - RCAF Comet 1A, c. 1953

Variants

Comet 1

The square-windowed Comet 1 was the first model produced, a total of 12 aircraft in service and test. Following closely the design features of the two prototypes, the only noticeable change was the adoption of four-wheel bogie main undercarriage units, replacing the single main wheels. Four 5,050 lb/st Ghost 50 Mk 1 (later 5,700 lb/st Ghost DGT3 series) engines were fitted. The span was 115 ft (35.05 m), length 93 ft (28.35 m), Maximum Takeoff Weight 105,000 lb (47.628 kg) with 36-48 passenger configurations.

An updated Comet 1A was offered with higher allowed weight and water-methanol injection; 10 were produced. In the wake of the 1954 disasters, all Comet 1s and 1As were brought back to Hatfield, first placed in a protective "cocoon" and retained for testing. All were substantially damaged in stress testing or were scrapped entirely.
Comet 1X: Two RCAF Comet 1As were rebuilt with heavier-gauge skins to a Comet 2 standard for the fuselage, and renamed Comet 1X.
Comet 1XB: Four Comet 1As were upgraded to a 1XB standard with a reinforced fuselage structure and oval windows. Both IX series were limited in number of pressurisation cycles.

DH 111 Comet Bomber

Originally proposed in 1948 as the "PR Comet", a "high level photo reconnaissance" adaptation of the Comet 1, de Havilland further developed a bomber variant to Air Ministry specification B35/46 as the DH 111 Comet Bomber with a submission to the Air Ministry on 27 May 1948. The substantially altered airframe powered by four 5,700 lb/st Ghost DGT3 engines, was designed around the "special bomb", and featured a "narrowed fuselage" along with a bulbous nose to accommodate the H2S Mk IX radar; the crew of four would be housed in a pressurized cockpit under a large bubble canopy. Additional fuel tanks carrying 2,400 gallons were built into the fuselage to attain a range of 3,350 miles. The DH 111 proposal was evaluated by the Royal Aircraft Establishment but serious concerns regarding weapons storage led to a negative RAE review. The capability of the proposed V bomber trio also made the DH 111 redundant and further development work at de Havilland was abandoned on 22 October 1948.

Comet 2

Picture - Comet C2 XK715 of No. 216 Squadron Royal Air Force at Filton Bristol in 1964.

The Comet 2 had a slightly larger wing, higher fuel capacity and more powerful Rolls-Royce Avon engines, which all improved the aircraft's range and performance; some of these changes had been made to make the aircraft more suitable for transatlantic operations. Following the Comet 1 disasters, these models were rebuilt with heavier gauge skin and rounded windows, and the Avon engines featuring larger air intakes and "outward-curving" jet tailpipes. A total of 12 of the 44-seat Comet 2s were ordered by BOAC for the South Atlantic route. The first production aircraft (G-AMXA) flew on 27 August 1953. Although these aircraft performed well on the South Atlantic routes, their range was still not suitable for the North Atlantic. All but four Comet 2s were allocated to the RAF with deliveries beginning in 1955. Modifications to the interiors allowed the Comet 2s to be used in a number of different roles. For VIP transport, the seating and accommodations were altered while provisions for carrying medical equipment including iron lungs was incorporated. Specialised ELINT and electronic survelillance capability was later added to some airframes.

Comet 2X: Limited to a single Comet Mk 1 powered by four Rolls-Royce Avon 502 turbojet engines and used as a development aircraft for the Comet 2.
Comet 2E: Two Comet 2 airliners were fitted with Avon 504s in the inner nacelles and Avon 524s in the outer ones. These aircraft were used by BOAC for proving flights during 1957-1958.
Comet T2: The first two of 10 Comet 2s for the RAF were fitted out as crew trainers, with the first aircraft (XK669) flying for the first time on 9 December 1955.
Comet C2: Eight Comet 2s originally destined for the civil market were completed for the RAF and assigned to No. 216 Squadron.
Comet 2R: Three Comet 2s were modified for use in radar and electronic systems development, initially assigned to No. 90 Group (later Signals Command) for the RAF. In service with No. 192 and No. 51 Squadrons, the 2R series were equipped to monitor Warsaw Pact signal traffic and operated in this role from 1958.

Comet 3

The Comet 3, which flew for the first time on 19 July 1954, was a lengthened Comet 2 powered by Avon M502 engines developing 10,000 lb/st with greater capacity and range, including the addition of wing pinion tanks. The Comet 3 was destined to remain a development series since it did not incorporate the fuselage-strengthening modifications of the later series aircraft, and was not able to be fully pressurised. Only two Comet 3s were constructed with G-ANLO, the only "flying" Comet 3, demonstrated at the Farnborough SBAC Show in September 1954. The only other Comet 3 airframe was not completed to production standard and was used primarily for ground-based structural and technology testing during development of the similarly sized Comet 4. Nine additional Comet 3 airframes were not completed and their construction was abandoned at Hatfield. In BOAC colours, G-ANLO was flown by John Cunningham in a marathon round-the-world promotional tour in December 1955. As a flying testbed, it was later modified with Avon RA29 engines fitted, as well as replacing the original long-span wings with reduced span wings as the Comet 3B and demonstrated in BEA livery at the Farnborough Airshow in September 1958. Assigned in 1961 to the Blind Landing Experimental Unit (BLEU) at RAE Bedford, the final testbed role played by G-ANLO was in "autoland" experiments. When retired in 1973, the airframe was used for foam arrester trials before the fuselage was salvaged at BAE Woodford, to serve as the mock-up for the Nimrod.

Picture - BOAC Comet 4C

Comet 4

The Comet 4 was a further improvement on the stretched Comet 3 with even greater fuel capacity. The design had progressed significantly from the original Comet 1, growing by 18ft 6in (5.64m) and typically seating 74 to 81 passengers compared to the Comet 1's 36 to 44. The Comet 4 was considered the definitive series, having a longer range, higher cruising speed and higher maximum takeoff weight. These improvements were possible largely because of Avon engines with twice the thrust of the Comet 1's Ghosts.

BOAC ordered 19 Comet 4s in March 1955, with G-APDA first flying on 27 April 1958. Deliveries to the airline began on 30 September 1958 with two aircraft. BOAC's G-APDC initiated the first transatlantic Comet 4 service and the first scheduled transatlantic passenger jet service in history, flying from London to New York with a stopover at Gander, Newfoundland on 4 October 1958. Rival Pan Am's inaugural Boeing 707 service began shortly afterwards.

BEA's Comets received a welcome response from crews and passengers but they were not so well liked by the baggage handlers. This was because the baggage/cargo holds had dorsal doors accessed directly underneath the aircraft, so each item of baggage or cargo had to be loaded upwards from the top of the cab of the baggage truck, through the little hole, then slid along the hold floor to be stacked inside. Likewise, the individual pieces of luggage and cargo had to be retrieved slowly with great effort on arrival.

American operator Capital Airlines ordered 14 Comet 4s in July 1956. The Comet 4A was designed for short-range operations and had a stretched fuselage with short wings (lacking the pinion (outboard wing) fuel tanks of the Comet 4). This order was cancelled but the aircraft were built for British European Airways (BEA) as the Comet 4B, with a further fuselage stretch of 38in (97cm) and seating for 99 passengers. The first Comet 4B (G-APMA) flew on 27 June 1959 and BEA aircraft G-APMB began Tel Aviv to London-Heathrow service on 1 April 1960.

Picture - DeHavilland Comet 4C cockpit

The last Comet 4 variant was the Comet 4C with the same longer fuselage as the Comet 4B coupled with the longer wings and extra fuel tanks of the original Comet 4, which gave it a longer range than the 4B. The first Comet 4C flew on 31 October 1959 and Mexicana began scheduled Comet 4C flights in 1960. The last two Comet 4C fuselages were used to build prototypes of the Hawker Siddeley Nimrod maritime patrol aircraft. Comet 4C (SA-R-7) was ordered by Saudi Arabian Airlines with eventual disposition to the Saudi Royal Flight for the exclusive use of King Saud bin Abdul Aziz. Extensively modified at the factory, the aircraft included a VIP front cabin, a bed, special toilets with gold fittings and was distinguished by a resplendent green, gold and white colour scheme with polished wings and lower fuselage that was commissioned from aviation artist John Stroud. Following its first flight, the special order Comet 4C was described as "the world's first executive jet."

Comet 5 design

The Comet 5 was proposed as an improvement over previous models, including a wider fuselage with five-abreast seating, a wing with greater sweep and podded Rolls-Royce Conway engines. Without support from the Ministry of Transport, the proposal languished as a "paper project" only.

Hawker Siddeley Nimrod

The last two Comet 4 fuselages produced were modified as prototypes to meet a British requirement for a maritime patrol aircraft for the Royal Air Force, designated Type HS 801. This variant became the Hawker Siddeley Nimrod and was built at the Hawker Siddeley factory at Woodford Aerodrome. Entering service in 1969, five Nimrod variants have been produced, with two still in service. While the highly modified Nimrod MRA4 was originally scheduled to enter service in 2003, however, following almost a decade of delays and overruns, the project was cancelled in the Strategic Defence and Security Review in October 2010. The Nimrod MR2 fleet was retired in 2010 and the Nimrod R1 Signals intelligence variant (three airframes) based at RAF Waddington in Lincolnshire, and flown by No. 51 Squadron will be retired in March 2011.

Aircraft on display

Picture - A preserved Comet 4C painted in BOAC livery.

Comet 1 The only complete surviving Comet 1 is a Comet 1XB on display at the RAF Museum Cosford, painted in BOAC colours with the registration G-APAS, although it never flew for that airline, having been delivered to Air France and then to the Ministry of Supply after conversion to 1XB standard. Mk 1A F-BGNX, the fuselage of which is preserved at the de Havilland Aircraft Heritage Centre in Hertfordshire, is the only surviving fuselage displaying the original "square" windows. The aircraft is currently under restoration.

The only complete surviving Comet 1 is a Comet 1XB on display at the RAF Museum Cosford, painted in BOAC colours with the registration G-APAS, although it never flew for that airline, having been delivered to Air France and then to the Ministry of Supply after conversion to 1XB standard.
Mk 1A F-BGNX, the fuselage of which is preserved at the de Havilland Aircraft Heritage Centre in Hertfordshire, is the only surviving fuselage displaying the original "square" windows. The aircraft is currently under restoration.

Comet 2 Comet C2 Sagittarius serial XK699, later maintenance serial 7971M) is displayed at the gate of RAF Lyneham in Wiltshire. Lyneham was previously the operational base for all RAF operated Comets.

Comet C2 Sagittarius serial XK699, later maintenance serial 7971M) is displayed at the gate of RAF Lyneham in Wiltshire. Lyneham was previously the operational base for all RAF operated Comets.

Picture - Comet 4C Canopus at the British Aircraft Heritage Museum, Bruntingthorpe Aerodrome

Comet 4 Comet 4B (Registration G-APYD) is stored at the Science Museum facility at Wroughton, Wiltshire. Comet 4C (Registration N888WA) is being restored and on display in BOAC livery at the restoration facility of the Museum of Flight at Paine Field next to Boeing's Everett, Washington widebody plant. It is being restored to its original Mexicana livery and interior. Comet 4C (Registration N777WA) is on display at the Parque Zoolx³gico Irapuato in Mexico. Comet 4 (Registration G-APDB) , is on display at the Imperial War Museum Duxford, England. Long displayed outdoors in Dan-Air colours as part of the Flight Line Display, it is now in BOAC livery in the new AirSpace building. Comet 4C (Registration G-BDIW) is on display at the Flugausstellung Leo Junior at Hermeskeil, Germany in Dan-Air colours. Comet 4C (Registration G-BDIX) is on display at the National Museum of Flight at East Fortune near Edinburgh, Scotland in Dan-Air livery. Comet 4C (Registration SU-ALM and later G-BEEX) on display at the North East Aircraft Museum, Sunderland, United Kingdom - Cockpit Section only. The last Comet to fly was Canopus (Serial XS235), which is kept in running condition at Bruntingthorpe Aerodrome, where fast taxi runs are regularly conducted.

Comet 4B (Registration G-APYD) is stored at the Science Museum facility at Wroughton, Wiltshire.
Comet 4C (Registration N888WA) is being restored and on display in BOAC livery at the restoration facility of the Museum of Flight at Paine Field next to Boeing's Everett, Washington widebody plant. It is being restored to its original Mexicana livery and interior.
Comet 4C (Registration N777WA) is on display at the Parque Zoolx³gico Irapuato in Mexico.
Comet 4 (Registration G-APDB) , is on display at the Imperial War Museum Duxford, England. Long displayed outdoors in Dan-Air colours as part of the Flight Line Display, it is now in BOAC livery in the new AirSpace building.
Comet 4C (Registration G-BDIW) is on display at the Flugausstellung Leo Junior at Hermeskeil, Germany in Dan-Air colours.
Comet 4C (Registration G-BDIX) is on display at the National Museum of Flight at East Fortune near Edinburgh, Scotland in Dan-Air livery.
Comet 4C (Registration SU-ALM and later G-BEEX) on display at the North East Aircraft Museum, Sunderland, United Kingdom - Cockpit Section only.
The last Comet to fly was Canopus (Serial XS235), which is kept in running condition at Bruntingthorpe Aerodrome, where fast taxi runs are regularly conducted.

Operators

Civilian operators

Picture - Aerolineas Argentinas Comet LV-PLM

Argentina

Aerolx­neas Argentinas ordered six Comet 4s in 1958 and they were delivered in 1959 and 1960, with a service introduction on 16 April 1959, between Buenos Aires to Santiago, Chile. Due to the loss of three aircraft, a replacement Comet 4C was bought in 1962. After being moved from international flights to domestic flights from 1966, the survivors were retired and sold to Dan-Air in 1971.

Australia

Qantas Empire Airways leased seven different Comet 4 aircraft in the early 1960s mainly to operate the Sydney to Singapore route.

Canada

Canadian Pacific Airlines ultimately had none in operation. One Comet 1A aircraft crashed on delivery and another was cancelled.

Picture - Olympic Airways Comet 4B at Manchester in 1966, showing engines buried in wing and revised round windows of all Comet 4s.

Sri Lanka (Ceylon)

Air Ceylon

East African Community (Kenya, Tanzania, Uganda)

East African Airways had two new Comet 4s delivered in 1960 and one Comet 4C delivered in 1962. Four other Comet 4s were leased from BOAC in the 1960s.

Ecuador

AREA Ecuador had one Comet 4 delivered in 1966 that was used on services between Quito and Miami. In 1968, the aircraft was impounded at Miami and remained under legal custody until scrapped in 1978.

Picture - United Arab Airlines (SU-ALD) de Havilland DH-106 Comet 4C, 1965 Le Bourget, credit: Alain Michot

Egypt

Egyptair inherited four surviving Comet 4Cs from United Arab Airlines in 1971 and sold these in the late 1970s.
Misrair had two new Comet 4C delivered in 1960. The airline became United Arab Airlines in 1960a.
United Arab Airlines inherited two Comet 4C from Misrair with seven new Comet 4Cs delivered in the 1960s. The airline became Egyptair in 1971.

France

Air France operated three new Comet 1A briefly in the 1950s before they were withdrawn.
Union Aéromaritime de Transport operated three new Comet 1As briefly in the 1950s, one was destroyed and two were withdrawn from service.

Greece

Olympic Airways had four new Comet 4Bs delivered in 1960, operated in a pooling arrangement with BEA.

Guatemala

Aviateca

Hong Kong

Hong Kong Airways

Kuwait

Kuwait Airways operated one second-hand Comet 4 and two new Comet 4Cs in the 1960s.

Lebanon

Middle East Airlines

Malaysia

Malaysian Airways operated five second-hand Comet 4s in the 1960s. The airline became Malaysia-Singapore Airlines in 1966.

Picture - British Airtours Comet 4B at Manchester Airport, July 1970.

Malaysia / Singapore

Malaysia-Singapore Airlines inherited five Comet 4s from Malysian Airlines in 1966 and two more Comet 4s in 1967 and 1968. All sold to Dan-Air London in 1969.

Mexico

Mexicana

New Zealand

Picture - Comet G-APDT at London's Heathrow Airport, being used for apprentice training with British Airways, c. 1976

Tasman Empire Airways

Portugal

Transportes Aereos Portgueses, between 1959 and 1962, chartered a British European Airways Comet 4B to operate a service between London and Lisbon.

Saudi Arabia

The Government of Saudi Arabia ordered a Comet 4C for use of King Saud bin Abdul Aziz. The Comet 4C was delivered in 1962 but crashed in 1963.

South Africa

South African Airways chartered two Comets from BOAC, 1953-1954.

Sudan

Sudan Airways operated two new Comet 4Cs in the 1960s and early 1970s.

United Kingdom

Picture - Dan-Air DH-106 Comet 4C, G-BDIW at the Flugausstellung Hermeskeil exhibit, credit: Klaus Nahr

BEA Airtours
British European Airways (BEA)
British Overseas Airways Corporation (BOAC) had a total of 10 Comet 1As delivered in the 1950s, with survivors withdrawn after the Cohen Inquiry findings. A total of 19 Comet 4s were delivered from 1957.
Channel Airways obtained five Comet 4Bs from British European Airways in 1970 and these were re-configured to a high-density 109-seat configuration for the inclusive tour charters from the United Kingdom. One aircraft was retired in 1971 as life-experienced, the remainder were obtained by Dan-Air when Channel went into receivership in 1972.
Dan-Air also known as Dan-Air London bought all the surviving flyable Comet 4s from the late 1960s into the 1970s. Some were for spares reclamation but most were operated on the carriers inclusive tour charters; a total of 48 Comets of all marks were inventoried.

Military operators

Picture - RCAF Comet 1X, #3501

Canada

Royal Canadian Air Force
412 Squadron (1953-1963) Comet 1A (later retrofitted to 1XB)

United Kingdom

Royal Air Force
51 Squadron (1958-1975) Comet C2 (RC)
192 Squadron (1957-1958) Comet C2 (RC)
216 Squadron (1956-1975) Comet C2 and C4
Royal Aircraft Establishment

Cancelled orders

Australia

British Commonwealth Pacific Airlines had placed various orders for Comets in the 1950s but the airline closed before any were delivered.

India

Air India

Brazil

Panair do Brasil had one Comet 2 on order but did not take delivery.

Japan

Japan Air Lines had three Comet 2s that were not completed. The airline originally ordered two aircraft in August 1952 and later increased the order to three, but the entire order was cancelled.

United States

Capital Airlines ordered the Comet 4 in July 1956 which were to be supplemented by 10 Comet 4As, a variant modified for Capital. Following financial problems and the takeover by United Airlines, the order was cancelled.
National Airlines ordered 12 aircraft, a mix of Comet 2s and Comet 3s in October 1953. The ordered was cancelled.
Pan American Airlines ordered three Comet 3s in October 1952 with options on a further seven. The order was cancelled.

Venezuela

Linea Aeropostal Venezolana had two Comet 2s on order that were not completed.

Accidents and incidents

The following major hull losses and accidents are sourced from Jet Airliner Production List (1992):

26 October 1952: Comet 1 G-ALYZ of BOAC crashed on takeoff from Rome-Ciampino Airport, Italy.
3 March 1953: Comet 1 CF-CUN of Canadian Pacific Airlines stalled on takeoff at Karachi, Pakistan.
2 May 1953: Comet 1 G-ALYV of BOAC crashed at Calcutta, India.
25 June 1953: Comet 1 F-BGSC of Union Aeromaritime de Transport skidded off a runway at Dakar, Senegal, damaged beyond repair.
15 July 1953: A BOAC Comet landed at Juhu Aerodrome instead of Santacruz Airport, Bombay. The aircraft was flown out some nine days later.
10 January 1954: Comet 1 G-ALYP of BOAC, operating Flight 781, crashed into the sea south of Elba, Italy.
8 April 1954: Comet 1 G-ALYY of BOAC, operating a charter as South African Airways Flight 201, crashed into the sea north of Stromboli, Italy.
13 September 1957: Comet 2R XK663 of No. 192 Squadron RAF damaged beyond repair in a hangar fire.
27 August 1959: Comet 4 LV-AHP of Aerolx­neas Argentinas flew into a mountain on approach to Asuncix³n, Paraguay.
20 February 1960: Comet 4 LV-AHO of Aerolx­neas Argentinas damaged beyond repair in a heavy landing at Buenos Aries-Ezeiza, Argentina.
23 November 1961: Comet 4 LV-AHR of Aerolx­neas Argentinas, operating Flight 322 hit a tree on takeoff at Sx£o Paulo, Brazil.
21 December 1961: Comet 4 G-ARJM of British European Airways crashed on takeoff from Ankara, Turkey.
19 July 1962: Comet 4 SU-AMW of United Arab Airlines crashed into a mountain 100km north-east of Bangkok, Thailand.
20 March 1963: Comet 4C SA-R-7 of the Saudi Arabian government crashed in the Italian Alps near Cuneo.
28 July 1963: Comet 4 SU-ALD of United Arab Airlines Flight 896 crashed into the sea near Bombay, India.
22 March 1964: Comet 4 G-APDK on lease to Malaysian Airlines damaged beyond repair landing at Singapore.
12 October 1967: Comet 4 G-ARCO of British European Airways suffered from a bomb explosion and crashed in the Mediterranean Sea, off the coast of Turkey.
28 December 1968: Comet 4Cs OD-ADQ and OD-ADR of Middle East Airlines both destroyed by Israeli troops in an attack at Beirut, Lebanon.
14 January 1970: Comet 4 SU-ANI of United Arab Airlines crashed at Addis Ababa, Ethiopia.
9 February 1970: Comet 4 SU-ALE of United Arab Airlines crashed after takeoff near Munich, West Germany.
3 July 1970: Comet 4 G-APDN of Dan-Air flew into the Monteseny mountains, north-west of Barcelona, Spain.
7 October 1970: Comet 4 G-APDL of Dan-Air damaged beyond repair after a wheels up landing at Newcastle Airport, England.
12 October 1970: Comet 4B G-ARCO of British European Airways Flight 284 crashed into the sea east of Rhodes following bomb explosion.
2 January 1971: Comet 4 SU-ALC of United Arab Airlines Flight 844 crashed near Tripoli Airport, Libya.

Specifications (Comet 4)

Picture - Comet 1 3-view in silhouette (note differences in Comet 4 insert, reproduced in same scale), credit: USAF Recognition Manual 355-10

Data from Jane's All The World's Aircraft 1965-66

General characteristics

Crew: 4 (2 pilots, flight engineer and radio operator/navigator)
Capacity: 56-81 passengers119 passengers could be accommodated in a special "charter seating" package in the later 4C series
Length: 111ft 6 in (33.99 m)
Wingspan: 114 ft 10 in (35.00 m)
Height: 29 ft 6 in (8.99 m)
Wing area: 2,121 sq ft (197m²)
Airfoil: NACA 63A116 mod root, NACA 63A112 mod tip
Empty weight: 75,400 lb (34,200kg)
Max takeoff weight: 162,000lb (73,5000kg)
Powerplant: 4x— Rolls-Royce Avon Mk 524 turbojets, 10,500 lbf (46.8kN) each

Performance

Maximum speed: 526mph (457 knots, 846km/h)
Range: 3,225 mi (2,800 nmi, 5,190km) (with 16,800 lb (7,620 kg) payload)
Service ceiling: 42,000ft (12,800m)

Related development

Hawker Siddeley Nimrod
Sud Aviation Caravelle

Comparable aircraft

Avro Canada Jetliner
Baade 152
Boeing 707
Convair 880
Douglas DC-8
Tupolev Tu-104
Tupolev Tu-110

Citations

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