Fatigue Failure Group 5

Background Turbojet engine invented in 1930 German’s first to fly jet powered aircraft in 1939 Aircraft improved during the Second World War British needed a long range mail plane after the war De Havilland company undertook the task Design concept changed to serve passenger flights Proposed design eventually named the DH 106 Comet in 1947

Aircraft Features All metal composed of advanced alloys Panels riveted and chemically bonded Flew at 490 mph Powered by 4 de Havilland Mk 150 Ghost turbojet engines Pressurized Cabin 36 seats Large windows Had kitchen, bar and restrooms Cost £250,000

Early Problems and Launch First flight at Farnborough Air Show in July 1949 Panel peeled off Rolls Royce Avon turbojet originally proposed in design Ghost Turbojet less powerful Skin made too thin to reduce weight Eventually certified airworthy in ,000 passengers flew in first year of service Notables included Queen Elizabeth and other members of royalty

Initial Accidents October 1952 – Plane crashes on take-off No casualties Blamed on pilot error March 1953 – Plane fails to become airborne 11 casualties Blamed on pilot error May 1953 – Plane disappears mid-flight Killing all 43 people on board Blamed on severe storm

Accidents of 1954 January Comet Aircraft explodes mid-flight Crashing into Mediterranean Killing all 35 on board March 1954 – Comet Aircraft breaks up after take off Aircraft breaks up as it reached it maximum height of climb Wreckage recovered near Naples Comet Aircrafts grounded by Ministry of Civil Aviation

Investigation Investigation carried out by RAE Model Aircrafts are put through re-pressurization and over-pressurization tests Results show that these accidents occurred as a result of metal fatigue failure

Reasons for Failure Research showed that the aircraft could not resist the strain of continuous pressurized climbs and descents The rectangular windows would begin to crack as the metal experienced stresses of up to 315MPa at the edge of windows and 70MPa of stress at each individual bolt position The small weaknesses would deteriorate rapidly under pressure, leading to the fuselage breaking up, causing an explosion Pre flight tests never accounted for this fatigue failure

Comet 4

Boing 707

Conclusions Revolutionary Someone had to fail for technology to advance Comet knew it was originally flawed, and hoped pilot skill would make up for it! Impartiality of 1953 enquiry was unhelpful. UFO’s were not responsible!!