Fatigue Failure

Group 5

BackgroundTurbojet engine invented in 1930German’s first to fly jet powered aircraft in 1939Aircraft improved during the Second World WarBritish needed a long range mail plane after the warDe Havilland company undertook the taskDesign concept changed to serve passenger flightsProposed design eventually named the DH 106 Comet in

1947

Aircraft FeaturesAll metal composed of advanced alloysPanels riveted and chemically bondedFlew at 490 mphPowered by 4 de Havilland Mk 150 Ghost turbojet

enginesPressurized Cabin36 seatsLarge windowsHad kitchen, bar and restroomsCost £250,000

Early Problems and LaunchFirst flight at Farnborough Air Show in July 1949Panel peeled offRolls Royce Avon turbojet originally proposed in designGhost Turbojet less powerfulSkin made too thin to reduce weightEventually certified airworthy in 195230,000 passengers flew in first year of serviceNotables included Queen Elizabeth and other members

of royalty

Initial AccidentsOctober 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 1954January 1954 - 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

InvestigationInvestigation 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 FailureResearch 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

ConclusionsRevolutionarySomeone had to fail for technology to

advanceComet 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!!