However, within a year of entering airline service, problems started to emerge, with three Comets lost within twelve months in highly publicised accidents, after suffering catastrophic in-flight break-ups. 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 The Comet was withdrawn from service and extensively tested.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 concentrations of stress around some of the square windows, were ultimately identified. As a result, the Comet was extensively redesigned, with oval windows, structural reinforcements 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 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. To read more of the originas, development and operational history of the Comet, click here. Specifications below are for the Comet 4. Details of the other models are in the above link.
