The dawn of the jet-age
(Part 2) The DH 106 Comet accident investigation
The first part of this series is here — I suggest you begin there
Today, it is unthinkable that so many accidents could have occurred to one aircraft type (such as the de Havilland D.H.106 Comet) without civil aviation authorities taking action sooner. But it must be remembered that aviation in the 1950s was nowhere near as safe as it is today. In 1953, for example, more than 53 civil aircraft accidents occurred. That number is greater if Soviet aircraft are added to western cargo and military transport crashes. With more than one accident a week on average, flying was regarded as risky. The reluctance of the authorities to implement a comprehensive review of the Comet’s early crashes must be looked at through this lens.
With the tragic failure of two more Comets in 1954, though, the entire fleet of those graceful and innovative airplanes was grounded indefinitely. The British government, with the prestige of the country’s aviation industry at risk, then launched a comprehensive review of the accident — the most detailed and far-reaching of any that had taken place thus far.
The Cohen committee
The British government’s first step was, of course, to establish an independent Commission of Inquiry. A renowned barrister and judge, Lord Cohen, chaired this committee, which included Sir Arnold Hall, Director of the Royal Aircraft Establishment of Farnborough.
That the Comet was not an easy aircraft to fly, was already widely known. Its use of innovative hydraulically powered flight controls (it was the first aircraft to have this feature which is now standard on all large jets), meant that the controls had no ‘feel’, and inexperienced pilots could easily over-control the aircraft. The two Comet takeoff accidents, in Rome and Karachi, were attributed to this. Another, a landing accident in June 1953 to a UAT (Union Aéromaritime de Transport; later UTA) Comet 1A on landing in Dakar, Senegal, was also attributed to pilot error. Until the advent of ‘full motion’ flight simulators, pilot training was, literally, a hit or miss affair.
But it was obvious to everyone that there was a bigger issue afoot than pilot training on the Comet. The previous investigation committee, led by Charles Abell of de Havilland, had elected to find “no fault” with the Comet in the January 1954 crash in Rome — by one vote. This time, however, commercial considerations were not allowed to interfere.
Writing the investigation rule-book
The Cohen committee took pains to investigate the accident from a scientific point of view. The exhaustive analysis employed to determine what actually happened to Comets G-ALYP and G-ALYY (‘Yoke Peter’ and ‘Yoke Yoke’ in the phonetic alphabet of the time), has been a template for aircraft accident investigations conducted ever since.
Early on, the committee decided to explore the possibility that catastrophic structural failure of the fuselage was the primary cause of the problem. The large water tank used in early pressurization tests was repurposed, and a complete fuselage, that of Comet G-ALYU (see picture above of Yoke Uncle in line service) donated by BOAC, was subjected to repeated simulated pressurization cycles. The intent was to see if repeated cycles could lead to accumulated stress and a catastrophic failure. Finally, after over 3,000 cycles a process that took six weeks to reach, the fuselage suddenly disintegrated.
Investigators found that the intact fuselage had fractured near one of the forward escape hatches. Analysis of the fuselage reassembled from recovered pieces of Yoke Peter (the first aircraft believed to have suffered from explosive decompression, in 1954) showed that that a crack had begun near a rivet hole close to a radio antenna housing. This was identified as the cause of the structural failure of the entire fuselage.
The report of the Court of Inquiry was delivered on February 1st 1955 and concluded that, “………the cause of the accident to Yoke Peter was the structural failure of the pressure cabin brought about by fatigue.”
Subsequently, more pieces of G-ALYP’s fuselage were recovered by chance in 1956, and other cracks were found to have originated near rivet holes close to the three front windows of the passenger cabin. The Comet’s characteristic rectangular windows had led to stress building up at the corners. However, this discovery was kept secret until 2015.
‘Metal fatigue’ was not a well-known phenomenon at the time, but after this accident it has been a primary concern of aircraft designers and manufacturers. To the credit of the British authorities, the findings of the Cohen committee were made public. The world’s aviation industry learned from the bitter experience of de Havilland and the D.H.106 Comet.
The race to fly again
With the fault identified, it became a race against time to incorporate the findings and redesign the Comet. Getting the aircraft re-certified and then returning it to commercial service would then become the focus.
But the sleeping giants across the Atlantic had awakened. Boeing, with all its experience in building large jets for the military, was racing to develop a civil jet-transport. Boeing’s arch-rival Douglas Aircraft, the dominant player in the airliner business since the days of the DC-3 , was playing catch-up. It was no longer a one-horse race and the Comet was not the favorite.
End of Part 2 — the final part is here.
This is part of a series on the propliners of the 1950s and the slow transition to the jet age. It all began with the DC-3 of course, and my columns move through the other Douglas propliners, the Boeing 377, Lockheed’s Electras and the elegant Constellation. The Brabazon Committee which sparked such a wave of innovation in the UK with the Vickers Viscount, the Bristol Britannia and the ill-fated de Havilland Comet. Many other significant aircraft, such as Avro Canada’s innovative but aborted C-102 passenger jet and the Sud-Aviation Caravelle, which led us into the start of the Jet Age, have columns too.
A few quirky segues I couldn’t resist: the ‘Double Sunrise’ flights between my two homelands Ceylon and Australia; the wonderful Carvairs and that very British habit of taking your car on holiday. I also had to write a paean to my beloved A380 and all my pilot friends in the Gulf as COVID ended that little dream.
Thanks for reading and I hope you enjoyed the series as much as I have relished writing them. My special thanks to my old friend, mentor, editor and repository of knowledge Roger Thiedeman, for all the encouragement and support throughout this project.
