Readers letters
In 1954 I was a (very) junior member of the structures department at the Royal Aircraft Establishment, and so a minor part of the investigation team into the Comet disasters.
Mike West and Roger Allen are correct that low cycle fatigue was the cause and that it was not understood at the time. As I remember it the failure originated at the corner of a rectangular astrodome cutout in the roof of the fuselage. The main stress was generated by the cabin pressure cycles. What I was told by senior members of the team was that cracks occurred at the corners of the cutout when forming the curved edges. A hole would have been drilled at the end of the crack to stop it running - normal practice in those days. The cutout had reinforcing plates on both sides. The three layers were riveted together, with plenty of chromate jointing, which would not have helped inspection. The scuttlebuck was that it was due to the use of carpenters (ex Mosquito workers) who had been converted to metalworkers, but who didn't really have the background of experienced metal workers. If so then management would have to bear responsibility. I have seen it said that the three layers should have been bonded, but that seems unlikely to me. Certainly the assemblies I saw were chromated - which acts as an anti fretting, anti corrosion gap filler. I started as an apprentice in the aircraft industry and this assembly would be entirely consistent with the practices of the day.
I had moved on, but later work established that the punch riveting procedure could initiate fatigue cracks more easily than drilled hole riveting, and indeed, on subsequent testing, fatigue cracks did start from rivet holes at window apertures. The Elba aircraft failure was traced to the roof aperture.
I stand to be corrected, but it seems to me that rather than design being to blame, it was lack of knowledge about the minute things that can affect fatigue failures, with, perhaps, the adoption of less than best practice work that was the cause. The company, and the country paid a heavy price for this failure. The global industry certainly learnt from it.
Remember as well that UK WW2 bombers were unpressurised and generally had short life. The American Fortresses were pressurised. Boeing therefore had quite a lot of experience.
If it is any comfort we were not the only ones to experience disaster. On the roll out of the first Boing 707 the undercarriage went up through the wing. It was another 9 months before the 'official' roll out. This 'disaster' was much easier to get overlooked than the Comet, but what if it had happened on a service aircraft landing with passengers aboard?
I agree that politicians (off all parties) were more damaging than Comet, but the industry didn't always help itself.
Mike Bowden, Exeter, Devon
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