1. COMET AIRCRAFT
Fatigue Failure
Group 6

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

3. 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

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

5. 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

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

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

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

9. Stress Concentrated at Windows

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

11. 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

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

13. Finally …
Thank You