comet

1. BOAC Flight 781BOAC Flight 781
Fatigue failureFatigue failure
ByBy
Kandagatla vinay kumarKandagatla vinay kumar
sandeepsandeep

2. INTRODUCTIONINTRODUCTION
 BOAC Flight 781 is an air craft of de Havilland DH.106BOAC Flight 781 is an air craft of de Havilland DH.106
Comet 1.Comet 1.
INCIDENT: The incident took place in 10 January 1954,INCIDENT: The incident took place in 10 January 1954,
when it took off from Ciampio airport in Rome,when it took off from Ciampio airport in Rome,
Italy and on the way to HeathrowItaly and on the way to Heathrow
airport inairport in London, England.London, England.

4. GENERAL ASSUMPTIONSGENERAL ASSUMPTIONS
 After approaching 27000 feet high the aircraft suffered an
explosive decompression and crashed into the
Mediterranean sea.
 Gerry Bull, a former BOAC engineer, said that when he
inspected the aircraft in Rome he looked for "incidental
damage". He did not find any, so he believed Flight 781
was fit to flight.

5. INVESTIGATIONINVESTIGATION
 To find out what caused the first failure, BOAC donated G-
ALYU ("Yoke Uncle") for testing.
 The airframe was put in a huge water tank and water was
pumped into the plane to simulate flight conditions.

6. Comet testing tankComet testing tank

7. TESTING PROCESSTESTING PROCESS
 In order to probe the origin of cabin explosion the cabin isIn order to probe the origin of cabin explosion the cabin is
subjected to alternate pressurization and De-pressurizationsubjected to alternate pressurization and De-pressurization
over 57 kpa over atmospheric pressure by repeatedlyover 57 kpa over atmospheric pressure by repeatedly
pumping water in to it and removing it. During suchpumping water in to it and removing it. During such
simulated cabin pressurization the wings of an aircraft weresimulated cabin pressurization the wings of an aircraft were
also stressed by hydraulic jack to mimic wing loadingalso stressed by hydraulic jack to mimic wing loading
during typical flight conditions after about 3000during typical flight conditions after about 3000
pressurization cycles a fatigue crack originating in thepressurization cycles a fatigue crack originating in the
cabin window until the metal skin was pierced,cabin window until the metal skin was pierced,

8. SECTIONAL VIEW OF CRACKSECTIONAL VIEW OF CRACK

9. Causes of FailureCauses of Failure
 Extensive testing gave theExtensive testing gave the
following reasons for failure:following reasons for failure:
 The failure was a result ofThe failure was a result of
metal fatigue caused by themetal fatigue caused by the
repeated pressurisation andrepeated pressurisation and
de-pressurisation of the airde-pressurisation of the air
craft cabin.craft cabin.
 Many investigators were ableMany investigators were able
to conclude that the crash hasto conclude that the crash has
been due to failure of window.been due to failure of window.

10. MANUFACTURING DEFECTSMANUFACTURING DEFECTS
 Another fact was that the supports around the windowsAnother fact was that the supports around the windows
were only riveted not glued, as the original specifications ofwere only riveted not glued, as the original specifications of
the air craft.the air craft.
 The problem was exacerbated by the punch rivet
construction technique employed. Unlike drill riveting, the
imperfect nature of the hole created by punch riveting
caused manufacturing defect cracks, which may have
caused fatigue cracks to start around the rivet. The
investigators examined the final piece of wreckage with a
microscope and found this defect.

11. CONCLUSIONCONCLUSION
 To overcome these defects the design of aircraftTo overcome these defects the design of aircraft
components must be done by considering pressures atcomponents must be done by considering pressures at
high altitudes and it should be examined thoroughly.high altitudes and it should be examined thoroughly.
 https://www.youtube.com/watch?https://www.youtube.com/watch?
v=_BZnn5OYcBcv=_BZnn5OYcBc

12.  Thank youThank you