De Havilland Comet

The de Havilland DH.106 Comet is a four-engine narrow body aircraft developed and manufactured by de Havilland in the United Kingdom. The world's first commercial jet airliner, the Comet 1 prototype first flew in 1949. It features an aerodynamically clean design with four de Havilland Ghost turbojet engines located 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 airliner's entry into service, three Comets were lost in highly publicised 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 The Comet was withdrawn from service and extensively tested.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 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.