1. Comet aircraft Fatigue failure Group 6

2. Background  de Havilland –Jet powered aircraft –Comet became first commercial jet airliner  First prototype flew 27th July 1949.

4. Background  Passenger flights began 1952  Tokyo – London flight time from 85 to 36 hours  Comet deemed a success –high pressure refuelling –hydraulic actuation of control surfaces –air-conditioned cabin.

5. Things go wrong  Soon after introduction, Comet 1 ran into difficulties. A string of accidents followed  March 1953, Comet CF-CUN –Crew killed during takeoff  May 1953, Comet G-ALYV –Plane disintegrates mid-air  January 1954, Comet G-ALYP –Plane explodes and crashes into sea killing all on board

6. Things go wrong  All Comet 1 aircraft subsequently withdrawn from service  Design modified and re-enters service. However…  April 1954, Comet GALYY –Ran into difficulty 30 mins into flight and crashed  12 th April 1954 –Certificate of airworthiness removed from Comet

7. Investigation  Crashes initially assumed due to unfamiliarity of pilots with new aircraft  De Havilland knew there could be problems with take-off performance and was relying on pilot skill to over-ride this  Weather also blamed  Evidence showed the aircraft suffered a catastrophic explosion of the fuselage

8. Causes of Failure  Extensive testing gave the following reasons for failure: –stresses of 315MPa at edge of rear ADF window and bolt hole around window of 70MPa stress at the bolt position –New technology introduced new load cases (high altitude flight for turbojet engines requiring cabin pressurisation)

9. Causes of Failure  Main cause of failure determined to be... Fatigue failure

10. Lessons Learned  Revision in estimates of safe loading strength requirements of airliner pressure cabins  Discovery that stresses around sharp-cornered cut-outs around pressure cabin apertures were considerably higher than had been appreciated –future jet airliners feature windows with rounded corners  Different materials used for specific situations  New testing methods

11. Technological Outcomes  Full-scale testing of aircraft structures utilised in future aircraft.  Better understanding of fatigue testing achieved  Concept of ‘one-bay’ crack tolerance in fuselage probably formulated

12. Re-design  Modifications made to design of aircraft and the Comet 4 re-entered service October 1958  Opened trans-Atlantic route with 80 passengers  A few weeks later Boeing 707 flew same route with 120 passengers and a safer, more flexible design engine  The loss of 6 years to the Comet problems instrumental in losing the lead in future jet transportation to the US  Only 113 produced  Production ceased 10 years after redesign

13.  Thank you!!