De Havilland Comet: the first jet airliner and the lesson of metal fatigue

Anyone boarding a jet today doesn’t think about fuselage skin, rivet holes and load cycles. That this is so, aviation owes in good part to an aircraft that was ahead of its time and failed because of exactly that: the de Havilland Comet. In 1952 it carried passengers at cruising altitude as the first jet airliner, drastically shortened flight times and, for a short time, made Britain the leading nation in civil aircraft building. Two years later the fleet was on the ground, and a water tank at Farnborough supplied the explanation: metal fatigue. This article tells the story of the Comet, explains the cause of the accidents in plain terms and shows you where you can still get the pioneer in front of your lens today.

The Comet in brief

The DH.106 Comet was the world’s first series-produced jet airliner. It was developed by the British de Havilland Aircraft Company at Hatfield, north of London. The prototype flew on July 27, 1949, and the first scheduled flight with paying passengers followed on May 2, 1952 with the state-owned BOAC. After a series of accidents, the Comet 1 lost its certificate of airworthiness in April 1954. The investigation revealed that the pressurized cabin had fatigued through repeated loading. With the redesigned Comet 4, the type returned in 1958, but by then the American competition had caught up.

From the Brabazon Committee to the first flight

The idea arose during World War II. A government committee under Lord Brabazon was to determine which airliners Britain would need after the war. Among the five concepts, as “Type IV,” was a proposal from Geoffrey de Havilland: a passenger aircraft with pure jet propulsion. That was bold, because until then jet engines were known almost only from military jets such as the company’s own de Havilland Vampire.

The result was an elegant aircraft with a moderately swept wing of around 20 degrees and four engines of the de Havilland Ghost type, which didn’t hang under the wings but sat in the wing roots. On July 27, 1949, the prototype with test pilot John Cunningham lifted off at Hatfield, soon afterward carrying the registration G-ALVG. In scheduled service at that time, only propeller aircraft flew.

What made the Comet so special

For passengers the difference was enormous. The Comet flew at a much higher altitude than the propeller aircraft, so above most of the weather, and at a cruising speed of around 740 km/h. That was much faster than the propeller aircraft BOAC had flown until then. Added to this were a calm, low-vibration cabin and an engine sound that had nothing in common anymore with the drone of piston engines. BOAC fitted the Comet 1 with 36 seats – a cabin for a well-paying clientele.

To fly at this altitude, the Comet needed a pressurized cabin that could withstand a much larger pressure difference from the outside air than on previous airliners. What that means for body and cabin is explained in our article on cabin pressure and cabin altitude. It was exactly this pressure difference that later became the problem.

1952: jet scheduled service begins

On May 2, 1952, the Comet G-ALYP took off on the first scheduled jet flight from London to Johannesburg, with several stopovers. More routes to Asia followed, and foreign airlines placed orders: Air France, the French UAT, Canadian Pacific and others wanted the new jet. For the British aviation industry it looked as if it had left the rest of the world behind by years. BOAC was the airline that opened the new era.

The accident series 1952 to 1954

After just a few months, the problems piled up. Within 18 months, five Comet 1s were lost. What matters: the accidents did not all have the same cause.

Date	Aircraft	Location	What happened	Fatalities
October 26, 1952	G-ALYZ (BOAC)	Rome Ciampino	failed to get airborne on takeoff, written off	none
March 3, 1953	CF-CUN (Canadian Pacific)	Karachi	takeoff accident at night	11
May 2, 1953	G-ALYV (BOAC)	near Calcutta	crash in a severe thunderstorm shortly after takeoff	43
January 10, 1954	G-ALYP (BOAC)	Mediterranean off Elba	broke apart in the climb after takeoff from Rome	35
April 8, 1954	G-ALYY (for South African Airways)	Mediterranean near Naples	broke apart in the climb after takeoff from Rome	21

The two takeoff accidents in Rome and Karachi put the aircraft’s takeoff behavior in the spotlight. The crash near Calcutta occurred in a violent storm. What was truly worrying, though, were the last two cases: two Comets each broke apart in the climb shortly after takeoff from Rome and plunged into the sea. Of all aircraft, G-ALYP, the aircraft of the inaugural flight, was the one lost off Elba.

Grounding, return, second grounding

After Elba, BOAC voluntarily grounded the Comets. Fires or engine damage were suspected, among other things, and a series of modifications was made. On March 23, 1954, the Comets flew again – only a good two weeks later, G-ALYY was lost near Naples. After that, the Comet 1 lost its certificate of airworthiness. It never flew for passengers again.

The investigation: wreckage from the seabed and a water tank

What followed is still regarded as a milestone of accident investigation. It was led by the Royal Aircraft Establishment (RAE) at Farnborough under Sir Arnold Hall. Two paths ran in parallel.

Why water? Had the fuselage been pumped up with air, the stored energy would have been released explosively on failure and destroyed the point of fracture. Water can hardly be compressed: the fuselage tears, but the traces stay readable.

What is metal fatigue?

Metal fatigue means that a component fails under repeated loading even though each individual load is far below its breaking point. You know it from bending a paper clip: it withstands bending once, and at the twentieth time it breaks.

On an aircraft this happens with every flight. On the ground the cabin is unpressurized, at cruising altitude it is under overpressure relative to the thin outside air, and after landing it is not again. The fuselage skin therefore stretches a little on every flight and relaxes afterward. Where the skin is interrupted – at windows, doors, hatches, antenna cutouts and at every rivet hole – the stress concentrates. At such places tiny cracks can form and grow a bit with every further cycle, until the remaining structure can no longer withstand the load.

Where the Comet cracked

The investigation of the Elba wreck traced the break to a cutout in the fuselage roof that was intended for an antenna of the automatic direction finder (ADF). A fatigue crack had formed at a rivet hole near the corner of this cutout. In the tank test, the failure began at the corner of an emergency exit hatch. Both show the same pattern: stress peaks at corners of cutouts, aggravated by rivet holes. Later evaluations also cite manufacturing details: the reinforcements around the cutouts are said to have been riveted instead of bonded as originally planned, and punching the rivet holes could create fine incipient cracks.

The board of inquiry under Lord Cohen sat in the fall of 1954. It considered the basic concept of the Comet sound but saw the cause of the two disasters in fatigue failure of the pressurized cabin.

What aviation learned from the Comet

The Comet investigation changed how aircraft are designed, tested and maintained. Many principles are so taken for granted today that their origin is forgotten.

• Fatigue tests on the whole aircraft: Instead of testing only individual components, new types today go through fatigue tests on complete airframes that simulate a multiple of the planned flight cycles.
• Rounded cutouts: Windows, doors and hatches have large corner radii and reinforced frames so that stress is distributed evenly.
• Fail-safe thinking: Structures are designed so that a crack is detected before it becomes dangerous and neighboring components take over the load. Crack stoppers in the fuselage limit how far a crack can run.
• Inspections by cycles: Maintenance programs count not only flight hours but also takeoffs and landings. How that works in practice is shown in our article on aircraft maintenance from A-check to C-check.

In this way the Comet indirectly made the competition safer too. The Boeing 707 and the Douglas DC-8 arrived in a world where the fatigue problem was understood.

The return: Comet 4 and the transatlantic race

De Havilland didn’t give up. The Comet 2 received oval windows and a strengthened structure; many of these aircraft went to the Royal Air Force. The Comet 3 remained a single prototype that flew on July 19, 1954 and served as the basis for the Comet 4. The Comet 4 was longer, more powerful and fitted with Rolls-Royce Avon engines. It first flew on April 27, 1958 and was delivered to BOAC in September 1958.

On October 4, 1958, BOAC used it to open the first jet scheduled service across the North Atlantic between London and New York. Westbound, the Comet 4 still needed a fuel stop at Gander. The return from New York to London took about six hours and twelve minutes. The lead was narrow, however: in the same month, Pan Am put the Boeing 707 into service on the New York–Paris route. The 707 was larger, faster and had more range – and its engines hung in nacelles under the wing, which made maintenance and later power increases easier. How Pan Am shaped the jet age in the US with the 707 is told in a separate article.

The Comet 4 family comprised three versions:

Version	Feature	Typical operators
Comet 4	long-range version, first flight 1958	BOAC, Aerolíneas Argentinas, East African Airways
Comet 4B	longer fuselage, shorter wing for European routes	BEA, Olympic Airways
Comet 4C	long fuselage with the Comet 4 wing	Mexicana, Middle East Airlines, Kuwait Airways, Sudan Airways and others

The short-haul version flew with British European Airways. Later the British charter airline Dan-Air collected used Comets in large numbers and in the end was the last airline in the world to operate the type. In November 1980 it retired the last Comet.

In parallel with the Comet, the Soviet Union developed the Tupolev Tu-104, which likewise carried engines in the wing roots. More on the development in the East is told in our overview of Soviet airliners.

Nimrod: the Comet with the RAF

Militarily the design lived on much longer. At Hawker Siddeley, the Comet 4 became the maritime patrol aircraft Nimrod, which you recognize by the weapons bay under the fuselage and the distinctive tail boom. The maritime patrol version MR2 retired in 2010, and the last Nimrods of the reconnaissance version R1 flew with the Royal Air Force until 2011. If you see a Nimrod in a museum today, you instantly recognize the Comet again in the cockpit windows and wing roots.

How to recognize a Comet

In a museum, the Comet is easy to tell from other classics if you watch for three things. The page on the De Havilland DH.106 Comet goes into detail on the type.

• Engines in the wing roots: Instead of nacelles under the wing, you see two air intakes on each side right at the junction of fuselage and wing.
• Slender fuselage, narrow nose: Next to a Boeing 707-320, the Comet looks delicate, with a nose that blends almost seamlessly into the cockpit.
• Windows: The Comet 1 has rectangular windows with rounded corners, later versions oval ones. That is how you tell early and late examples apart at a glance.
• On the Comet 4 and 4C: Fuel pods at the leading edge of the wings that project forward like small nacelles.

Where you can still see the Comet today

You won’t see a Comet fly anymore, but several examples survive. For spotters with a sense of history, a little Comet tour is worthwhile.

Example	Version	Location
G-BDIW	Comet 4C (ex Dan-Air)	Flugausstellung Hermeskeil, Germany
G-APDB	Comet 4	IWM Duxford, England
G-APAS	Comet 1XB, the only complete Comet 1	RAF Museum Cosford, England
F-BGNX	Comet 1A, fuselage only	de Havilland Aircraft Museum, England
G-BDIX	Comet 4C	National Museum of Flight East Fortune, Scotland
N888WA	Comet 4C	Museum of Flight, restoration center in Everett, USA

For visitors from Germany, Hermeskeil in the Hunsrück is the easiest way to a Comet – a former Dan-Air Comet 4C stands there. The fuselage F-BGNX at the de Havilland Aircraft Museum is especially fascinating: it was built in 1953 as a Comet 1A for Air France, later brought to Farnborough as a spare fuselage for the tank tests, but never tested there. So here you can see up close exactly the fuselage shape with the early windows that the whole story revolves around. For Duxford, the spot guide IWM Duxford helps you, for Cosford the spot guide RAF Museum Cosford, for Scotland the guide to the National Museum of Flight.

A word on currency: exhibition locations and accessibility can change, for example through restorations or renovations. Check the respective museum’s information before a visit. If the history of the British jet pioneers fascinates you, the history of the Concorde is also a good next step – it closes the circle, because Britain played the leading role there too.

Conclusion

The de Havilland Comet was a pioneer in the best and the bitterest sense. In 1952 it showed that passengers can travel fast and high with jet engines, and it paid for the fact that nobody had properly understood the effects of thousands of pressure cycles on an aircraft cabin. The thorough investigation, with wreckage recovery off Elba and the water tank at Farnborough, turned this catastrophe into knowledge that has made every later airliner safer. Commercially the 707 and DC-8 reaped the rewards – technically, a piece of the Comet is in every jet you photograph at the fence today.