COMET AIRCRAFT Fatigue Failure Group 6

THE COMET - BACKGROUND De Havilland Engines Aircraft Standard piston engines before 1929 First commercial airline using turbojet engines

THE COMET - BACKGROUND Passenger flights began 1952 London – Johannesburg flight time from 40hrs to 23hrs Comet deemed a success Fully pressurised cabin Quiet & smooth flight Flew 28,000 passengers in first year

Human Factors British v’s Americans Politics, time, market pressures 3 years testing, not 7 BOAC concerns over fatigue Fleet in service before testing

INITIAL ACCIDENTS 1952 – Accident on take off Blamed on pilot error 1953 – Failed to gain altitude Initially blamed on pilot error Subsequently found to be design flaw in wing Calcutta accident – plane disintegrated Blamed on tropical storm

INITIAL ACCIDENTS 1954 - Comet explodes over Mediterranean Flights Suspended & recovery of wreckage Design modified: Shields between engines and fuel tanks However ... 2 months later ... Yet another accident Comet flying from Rome disappeared Wreckage retrieved from the sea

The Real Problem Investigation began Large water tank = cabin loading Wings flexed by hydraulic jacks = flexing due to wind load

The Real Problem Sudden pressure drop at equivalent of 9000 flight hours Corners of square windows – high stress concentration

Stress Concentrated at Windows

METAL FATIGUE The Real Problem Navy recovers 70% of wreck & confirms test results METAL FATIGUE

Lessons Learned Unforeseeable possibilities – 1st jet airliner Fatigue failure Minimising stress concentrations Materials for specific situations New aircraft testing Testing to simulate ‘real life’ conditions

Redesigned as Comet 4 First scheduled trans-atlantic service 113 produced Production ceased 1968

Finally … Thank You