Table of Content
• Features of The
02. The Occurence
• What is Fatigue?
04. The Real Reason
and How we could
have avoided it?
Key features – Aluminium construction – Hydraulic actuation of
the control surfaces – Four de Havilland Ghost Jet engines
(4450lbs thrust each) – 36 passengers – Range 1750 miles (2800
km) – Cruising speed 490 mph (780 kmh-1) – Cruising altitude
35000 ft (10.6 km) – Weight 107,000 lbs (49,000 kg)
The de Havilland DH.106 Comet was the world's first commercial jet
airliner. Developed and manufactured by de Havilland at its Hatfield
Aerodrome in Hertfordshire, United Kingdom, the Comet 1 prototype first
flew in 1949.
About haviland Comet
• 2 MAY 1953 • 10 JANUARY 1954
BOAC Flight 781 suffered an explosive decompression at
altitude and crashed, killing all 35 people on board.
BOAC Flight 783 broke up mid-air and crashed after encountering a
severe squall, shortly after taking off from Calcutta (now Kolkata),
India. All 43 passengers and crew on board were killed.
The horrific incidents continued till 1954.
Stress is the ratio of force over area (S
=R/A, where S is the stress, R is the internal
resisting force and A is the cross-sectional
area). Strain is the ratio of change in
length to the original length, when a given
body is subjected to some external force
(Strain= change in length÷the original
The above picture shows the stress-stength curve
Metals will break under a load that is
repeatedly applied and then removed,
though they can support a much larger
steady load without distress.
The investigation explored a number of avenues, and finally gave structural failure of the pressure cabin brought about by
fatigue as the cause of the accidents. The use of fracture mechanics methods not used in 1954 has enabled the analysis of
these fatigue cracks to be made, and the initial defect size has been estimated to be approximately 100 μm in the case of G-
ALYP. This is not incompatible with the manufacturing techniques of the time, and information regarding cracks in the cabin
identified during manufacture.
The Real Reason
o The failure of the pressure cabin was brought about by
fatigue (In agreement with the 1954 findings)
o The manufacturing process of punch riveting (rather than
drill, rivet and glue) caused small cracks which grew under
the repeated loading of the pressure cabin
o The bolt hole which failed on ‘YP’ had a defect in the
chamfer which indicated the potential for manufacturing
defects on all skin holes
o The interaction of the skin stresses and the
manufacturing defects was beyond the scientific
knowledge base of the early 1950s
fatigue, exacerbated by the squarish window design. Engineers
redesigned the structure of the The cause of the two planes
breaking up in mid-flight was found. It was metal plane, including
adding rounded off windows, for what became the Comet 2, and that
was the end of that issue
Micro-structural picture of the cracks formed near the windows.
HOW IT COULD HAVE BEEN AVOIDED!
• The metals used for manufacturing should be pure without any defect
• To reduce the stress on the most stress region such as the window region, the window shape should be oval shaped
Modern Airplane Windows
• The Comet is widely regarded as both an adventurous step forward and a supreme tragedy;the aircraft's legacy includes
advances in aircraft design and in accident investigations.
• According to de Havilland's chief test pilot John Cunningham, who had flown the prototype's first flight, representatives from
American manufacturers such as Boeing and Douglas privately disclosed that if de Havilland had not experienced the Comet's
pressurisation problems first, it would have happened to them.Cunningham likened the Comet to the later Concorde and added
that he had assumed that the aircraft would change aviation, which it subsequently did.Aviation author Bill Withuhn concluded
that the Comet had pushed "'the state-of-the-art' beyond its limits."
• Aeronautical-engineering firms were quick to respond to the Comet's commercial advantages and technical flaws alike; other
aircraft manufacturers learned from, and profited by, the hard-earned lessons embodied by de Havilland's Comet
"I don't think it is too much to say that the world changed from the moment the Comet's wheels left the ground ."
-Tony Fairbrother, manager, upgraded Comet development.