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

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