The de Havilland Comet was the most beautiful airliner ever built. It was also the most deadly — and its failures saved more lives than any single aircraft in history. We’ve written about the Comet before — see our earlier piece on its legacy. This article focuses on the investigation that changed aviation forever. When the Comet 1 entered service with BOAC on May 2, 1952, it was a revolution. Passengers stepped aboard an aircraft that flew twice as fast, twice as high, and infinitely smoother than any propeller-driven airliner. The cabin was pressurised to a comfortable altitude. The engines — four de Havilland Ghost turbojets buried in the wing roots — were virtually vibration-free compared to piston engines. For the first time, crossing the Atlantic felt like the future. Then the future started falling out of the sky.

Three Comets Lost

On January 10, 1954, BOAC Flight 781 disintegrated at 29,000 feet shortly after takeoff from Rome. All 35 people aboard were killed. The wreckage fell into the Mediterranean near the island of Elba. The Comet fleet was grounded. Engineers inspected every airframe, found nothing conclusive, and returned the type to service. Fifteen days later, on April 8, 1954, South African Airways Flight 201 — a BOAC-operated Comet — broke apart at altitude near Naples. Twenty-one dead. The Comet was grounded permanently. A third Comet had already been lost: BOAC Flight 783 crashed on takeoff from Calcutta in May 1953 during a violent storm, but this was attributed to structural overload in turbulence — a design problem, but a different one.

“The Comet disasters led to the most important and far-reaching investigation in aviation history. Every modern airliner flies more safely because the Comet failed first.”
— Royal Aeronautical Society, on the legacy of the Comet investigations

The Investigation That Changed Everything

The Royal Aircraft Establishment at Farnborough launched the most thorough accident investigation the world had ever seen. Engineers recovered wreckage from the Mediterranean seabed — a pioneering underwater salvage operation — and painstakingly reconstructed the fuselage of Flight 781. Then they did something no one had attempted before. They took a complete Comet fuselage, placed it in a water tank, and subjected it to repeated pressurisation cycles — inflating and deflating the cabin thousands of times to simulate years of service. After the equivalent of 3,060 flights, the fuselage burst. The crack originated at the corner of a square window — specifically, at a rivet hole near the automatic direction finder (ADF) antenna cutout in the roof. Under repeated pressurisation loads, microscopic cracks formed at stress concentration points around the square-cornered openings. After roughly 1,000 flight cycles, these cracks propagated through the skin until the fuselage failed catastrophically.

TIL the world’s first commercial jet airliner, the De Havilland Comet, suffered numerous fatal crashes in the 50’s because the windows were square

Square Windows Kill

The discovery was devastating in its simplicity. Square corners concentrate stress. Round corners distribute it. Every subsequent airliner — without exception — has used oval or round passenger windows. The Comet’s square windows were not the only factor (the fuselage skin was also thinner than it should have been, and the rivet holes created additional stress risers), but they became the iconic lesson. More broadly, the Comet investigation established the discipline of metal fatigue analysis in aviation. Before the Comet crashes, fatigue was poorly understood and rarely tested. After them, every aircraft manufacturer was required to demonstrate that their designs could withstand tens of thousands of pressurisation cycles without failure. The fail-safe design philosophy — build structures so that a crack in one element does not cause catastrophic failure — became standard.

The Bitter Irony

De Havilland redesigned the Comet with oval windows, thicker skin, and structural improvements. The Comet 4 entered service in 1958 and was perfectly safe. But it was too late. Boeing had used the years of the Comet’s grounding to develop the 707, which was bigger, faster, and more economical. The 707 defined the jet age. The Comet, which should have owned it, became a footnote. The Comet killed 99 people in two crashes. The investigation it triggered has saved hundreds of thousands. No airliner since has suffered a pressurisation-fatigue failure of the kind that destroyed Flights 781 and 201. That is the Comet’s true legacy: the beautiful jet that taught the world how aircraft actually break.

“The Comet was a beautiful aircraft. It was smooth, quiet, and fast. Passengers loved it. But it was built at the very edge of what metallurgy understood, and the edge was not far enough.”
— Bill Withers, de Havilland test engineer

Sources: FAA Lessons Learned, RAF Museum, Admiral Cloudberg, Plane and Pilot, New Atlas