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 1952
 30,000 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
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No casualties
Blamed on pilot error
 March 1953 – Plane fails to become airborne
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11 casualties
Blamed on pilot error
 May 1953 – Plane disappears mid-flight
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Killing all 43 people on board
Blamed on severe storm
Accidents of 1954
 January 1954 - Comet Aircraft explodes mid-flight
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Crashing into Mediterranean
Killing all 35 on board
 March 1954 – Comet Aircraft breaks up after take off
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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!!