The Mystery: What was causing the crashes of the pioneering de Havilland Comet jet?
The Backstory: When it comes to lists of milestone aviation achievements, the de Havilland Comet jetliner is often mentioned prominently. It was not only the first jet airliner, but many regard it as one of the most beautiful aircraft of all time. Others note that its place in history is assured as a design with an early history of mysterious, catastrophic fatal crashes.
Commissioned in the early 1940s by the British government in its quest to find a fast and capable mail plane, famed designer Geoffrey de Havilland answered the call with the Comet, a jet-powered design that would likely be the first such plane in history. The idea was risky. Jet engines were more reliable than large-piston radial engines, like those that powered the rival Lockheed Constellation. Those double-row radial engines were expensive, difficult to maintain and prone to mechanical problems. Turbofans, which are the engine of choice in jet planes today, had not yet come into general use, and the turbojets of the day were fuel guzzlers. Despite this, de Havilland won the competition and began work on the Comet. In 1952, the company delivered the first DH 106 to British Overseas Airways Corporation (BOAC). Other customers appeared, including British European Airways and the British government.
The engines on the first plane were the Halford H.2 Ghost 50 turbojets; they were buried in sleek enclosures in the wing root. If there were going to be troubles with the plane, the new engines, observers worried, were predicted as the likely cause, but they weren’t. Something much worse was.
The first disaster took place in January 1954, around two-and-a-half years after the first Comet delivery, when the first production Comet, operated by BOAC, broke up in mid-air over the Mediterranean Sea 20 minutes after taking off from an airport in Italy. All 36 people aboard died in the accident. Investigators suspected sabotage, fire, flutter and an explosion in a fuel tank. After recovering and examining much of the debris from the plane, the committee heading up the inquiry declared, incorrectly as history would prove, that the plane wasn’t the problem.
De Havilland, which had voluntarily grounded the small fleet, in March okayed the planes for flight once more. But then, in April, another Comet, this one operated by South African Airways, came apart in midair, again over the Mediterranean. All 21 aboard lost their lives.
The Comet was grounded, this time permanently, and its certification was revoked. De Havilland went to work finding the root cause. A few months later, it solved the mystery.
The Truth: By testing the structure of an existing Comet in a water tank under repeated pressurization cycles, the truth became clear when the fuselage of the test article came apart in an explosive decompression. This was after just over 3,000 pressurization cycles. The cause of the two planes breaking up in mid-flight was found. It was metal fatigue, exacerbated by the squarish window design. Engineers redesigned the structure of the plane, including adding rounded off windows, for what became the Comet 2, and that was the end of that issue. The company went on to produce 114 of the aircraft, ending with the Comet 4 model, which was last produced in 1959.
Sadly, the Comet, even after the cause of its mystery woes was diagnosed, had a terrible safety record, with 26 hull losses during its short operational life, resulting in more than 400 fatalities.
But its role as a pioneer helped pave the way for future airliners, and de Havilland’s discovery of the dangers of metal fatigue from pressurization cycles made future airliners far safer from that danger than before. Although a few explosive depressurizations have occurred since that time, the designs of the planes that suffered them were quickly modified to cut down or arguably eliminate such future risks.