Readers letters
I cannot dispute the interesting information given by Mike Bowden with regard to the cause of the Comet disasters being the design of the rectangular astrodome cut-out in the roof of the fuselage (Letters, PE April). But de Havilland at Hatfield concentrated their investigations on the fuselage windows and escape hatches.
In September 1954, I had just finished my first year of an apprenticeship at the de Havilland technical school and was sent to the experimental department of the factory. This large department was mainly involved in constructing and testing samples of the windows and escape hatches, bolted and sealed to a steel frame.
Each sample was repeatedly pressurised hydraulically to simulate the fuselage cabin pressure cycles. I can distinctly remember seeing, at a certain number of cycles (1,300 comes to mind although this seems now to be too many), cracks appearing at the external corners of the rectangular windows' frames or escape hatches. When any of these tests were repeated, the failure point always occurred at the same number of cycles plus or minus a small margin.
As result of this testing, major design modifications were implemented which mainly consisted of a second external fuselage skin over the entire length of the fuselage side windows and escape hatch areas riveted to the original fuselage skin and frames.
This modification was applied to a number of Comet 1s, 1As and possibly Comet 2s originally delivered to BOAC, Air France and, I think, a Canadian buyer respectively.
Sadly, 1954 & 1954 were difficult years for de Havilland not just because of the Comet disasters but also because of other major projects. The DH110 (later to become the Sea Vixen) second prototype was undergoing intensive flight testing following the terrible first prototype's crash at Farnborough, and behind closed curtains there was a full-scale mock-up of the Trident original design which was never built.
This was because the government owned BEA, who had ordered the plane off the drawing board, insisted on a significant seat capacity reduction at a late stage and thus ruined the international sales prospects with other airlines.
Boeing took advantage and soon after produced the similar but larger and very commercially successful 727 – paradoxically with three engines when the 737 had only two engines.
J David Tingle, Codicote, Herts
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