The de Havilland DH.106 Comet was the world's first commercial jet airliner. Developed and manufactured by de Havilland in the United Kingdom, the Comet 1 prototype first flew in 1949. It featured an aerodynamically clean design with four de Havilland Ghost turbojet engines buried in the wing roots, a pressurised cabin, and large windows. For the era, it offered a relatively quiet, comfortable passenger cabin and was commercially promising at its debut in 1952.
Within a year of the airline's entry into service, three Comets were lost in highly publicized accidents after suffering catastrophic mishaps mid-flight. Two of these were found to be caused by structural failure resulting from metal fatigue in the airframe, a phenomenon not fully understood at the time; the other was due to overstressing of the airframe during flight through severe weather. The Comet was withdrawn from service and extensively tested. Design and construction flaws, including improper riveting and dangerous stress concentrations around square cut-outs for the ADF (automatic direction finder) antennas were ultimately identified. As a result, the Comet was extensively redesigned, with structural reinforcements and other changes. Rival manufacturers heeded the lessons learned from the Comet when 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 remained in commercial service until 1981. The Comet was also adapted for a variety of military roles such as VIP, medical and passenger transport, as well as surveillance; the last Comet 4, used as a research platform, made its final flight in 1997. The most extensive modification resulted in a specialised maritime patrol derivative, the Hawker Siddeley Nimrod, which remained in service with the Royal Air Force until 2011, over 60 years after the Comet's first flight.
Development
Origins
On 11 March 1943, the Cabinet of the United Kingdom formed the Brabazon Committee, which was tasked with determining the UK's airliner needs after the conclusion of the Second World War. One of its recommendations was for the development and production of a pressurised, transatlantic mailplane that could carry of payload at a cruising speed of non-stop. Aviation company de Havilland was interested in this requirement, but chose to challenge the then widely held view that jet engines were too fuel-hungry and unreliable for such a role. As a result, 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; proposing a specification for a pure turbojet-powered design.
The committee accepted the proposal, calling it the "Type IV" (of five designs), and in 1945 awarded a development and production contract to de Havilland under the designation Type 106. 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 (), 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 small passenger compartments 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 created, the order total was revised to 10.