De Havilland Comet

DH 106 Comet
British European Airways (BEA) Comet 4B arriving at Berlin Tempelhof Airport in 1969
Role	Narrow-body jet airliner
Manufacturer	de Havilland
First flight	27 July 1949
Introduction	2 May 1952 with BOAC
Retired	14 March 1997 (Comet 4C XS235)
Status	Retired
Primary users	BOAC British European Airways Dan-Air Royal Air Force
Number built	114 (including prototypes)
Unit cost	Comet 1: £275,000 (1952)
Developed into	Hawker Siddeley Nimrod

The de Havilland DH 106 Comet was the world's first commercial jetliner. Developed and manufactured by de Havilland at its Hatfield Aerodrome, Hertfordshire, United Kingdom headquarters, the Comet 1 prototype first flew on 27 July 1949. It featured an aerodynamically clean design with four de Havilland Ghost turbojet engines buried in the wings, a pressurised fuselage, and large square windows. For the era, it offered a relatively quiet, comfortable passenger cabin and showed signs of being a commercial success at its 1952 debut.

A year after entering commercial service, the Comets began suffering problems, with three of them breaking up during mid-flight in well-publicised accidents. Two of these were found to be caused by catastrophic failure resulting from metal fatigue in the airframes, not well understood at the time. The other one was due to overstressing of the airframe during flight through severe weather. The Comet was withdrawn from service and extensively tested to discover the causes of the fatigue failures. Design flaws, including dangerous stresses at the corners of the square windows and installation methods, were ultimately identified. As a result, the Comet was extensively redesigned with oval windows, structural reinforcement, and other changes. Rival manufacturers meanwhile heeded the lessons learned from the Comet while developing their own aircraft.

Although sales never fully recovered, the improved Comet 2 and the prototype Comet 3 culminated in the redesigned Comet 4 series which debuted in 1958 and had a productive career of over 30 years. The Comet was adapted for a variety of military roles such as VIP, medical and passenger transport, as well as surveillance. The most extensive modification resulted in a specialised maritime patrol aircraft variant, the Hawker Siddeley Nimrod. Nimrod remained in service with the Royal Air Force (RAF) until June 2011, over 60 years after the Comet's first flight.

On 11 March 1943, the Cabinet of the United Kingdom formed the Brabazon Committee to determine the UK's airliner needs after the conclusion of the Second World War. One of its recommendations was for a pressurised, transatlantic mailplane that could carry non-stop, one long ton (1.0 t) of payload at a cruising speed of 400 mph (640 km/h). De Havilland chose to challenge the widely held scepticism of jet engines as too fuel-hungry and unreliable, So committee member Sir Geoffrey de Havilland, head of the de Havilland company, used his personal influence and his company's expertise to champion the development of a jet propelled aircraft; and proposed a specification for a pure turbojet-powered design. The committee accepted the proposal, calling it the "Type IV" (of five designs), and awarded a development and production contract to de Havilland under the designation Type 106 in February 1945. The type and design were to be so advanced that De Havilland had to undertake the design and development of both, the airframe, and the engines. This was because in 1945 no turbojet engine manufacturer in the world was drawing up a design specification for an engine with the thrust and specific fuel consumption, that could power an aircraft at the proposed cruising altitude (40 thousand feet), speed, and transatlantic range as was called for by the Type 106. First-phase development of the DH 106 focused on short and intermediate range mailplanes with a small passenger compartment and as few as six seats, before being redefined as a long-range airliner with a capacity of 24 seats. Out of all the Brabazon designs, the DH 106 was seen as the riskiest both in terms of introducing untried design elements and for the financial commitment involved. Nevertheless, the British Overseas Airways Corporation (BOAC) found the Type IV's specifications attractive, and initially proposed a purchase of 25 aircraft; in December 1945, when a firm contract was laid out, the order total was revised to 10.