On 7 April 1954, Peter Duffey co-piloted the sleek, four-engined de Havilland Comet G-ALYY into Heathrow Airport. It was the last leg of the new scheduled British Overseas Airways Corporation (BOAC) jet passenger flight between London and Johannesburg.

Some 36 hours later, with a new crew on board, the aircraft took off from Rome for the second stage of its return journey to South Africa. It began to climb to its cruising altitude. Shortly after passing Naples, over the island of Stromboli at the southern tip of Italy, the aircraft disintegrated. Seven crew and 14 passengers were killed.

It was the second mid-air explosion of a Comet in three months.

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“I still do not forgive those who restarted the services after the [first] crash,” says Duffey, now retired and living in Canada. “They gambled and lost; I was one of the chips.”

The first Comet was rolled out of its hangar at the de Havilland factory in Hatfield, some 25 miles (40 kilometres)  north of central London, in July 1949 – only four years after the end of World War Two.

Passenger aircraft of the time were low-flying and uncomfortable to ride. With unpressurised cabins and propellers powered by noisy piston engines, they had to fly through, rather than above, the weather. Many were converted from wartime bombers or freight transport aircraft and had quaint old-fashioned names such as Tudor, Lancastrian and Argonaut.

The Comet, on the other hand, looked like an aircraft from the future, with a mirrored aluminium fuselage and swept back wings concealing four jet engines. Along each side were large rectangular picture windows to afford passengers unprecedented views of the Earth from a cruising altitude of up to 40,000ft (12 kilometres).

It was the Concorde of its day – it flew higher, faster, smoother than any other airline of that time and made everything else obsolete – Alistair Hodgson, de Havilland Museum  

“It still looks modern,” says Alistair Hodgson, curator of the de Havilland Aircraft Museum. “It was clean, it was aerodynamic and it looked like it would slip through the air perfectly – and of course, that’s what it did.”

“There’s an old saying in the aviation industry that if an aeroplane looks right, it’ll fly right,” says Hodgson. “It was the Concorde of its day – it flew higher, faster, smoother than any other airline of that time and made everything else obsolete.”

Inside there were seats for 36 passengers in two cabins. Those in first class were seated around tables – much like in a railway carriage. Apart from the cockpit, the rest of the fuselage was taken up by a large galley, luggage storage areas (there was no hold underneath) and separate toilets for ladies and gentlemen.

“That’s what happens when you allow engineers to design aircraft, rather than accountants,” says Hodgson. “If you look at a modern no-frills airline, every inch of space is given over to fare-paying passengers but that’s not what air travel was like in the 1940s.

“Air travel was just in its final days of being a thing for the rich only,” he says. “The primary way of travelling long distances was ocean liners.” In fact, many of the passengers of BOAC were civil servants off to run the British Empire.

After almost two years of test flights, the Comet made its first scheduled flight on 2 May 1952, flying – via Rome, Beirut, Khartoum, Entebbe and Livingstone – to Johannesburg. The flight, taking just over 23 hours, was a triumph. Passengers reported a smooth journey, superb service and beautifully presented meals.

With no other passenger jets yet in service, the Comet was the envy of the world. “The Comet fleet considered themselves the elite in BOAC,” says Hugh Dibley, a pilot with the airline in the 1960s. “It even had its own special call-sign: ‘Jet Speedbird’.”

Within months, BOAC had added flights to Ceylon (now Sri Lanka), Karachi, Singapore and Tokyo. Meanwhile, de Havilland was notching up new orders for its remarkable aircraft from Canadian Pacific, Air France and the Royal Canadian Air Force.

The first four aircraft had faulty seals - we used to carry hydraulic fluid to top up the system – Peter Duffey, Comet pilot  

At speeds of up to 500mph (807km/h), passengers were experiencing the ride of their life. But for those sitting at the sharp end, there were few flights that were without incident.

“All my time on the Comet 1, the aircraft was still under development,” says Duffey. “We had problem after problem.”

The Comet was the first commercial airliner with hydraulic flying controls, which worked much like the brake pedal on a car. When the pilot moved the control column, it activated a pump which pushed fluid through a circuit of pipes to adjust the control surfaces on the wings.

“The first four aircraft had faulty seals,” says Duffey. “We used to carry hydraulic fluid to top up the system.”

Crews also reported a host of other problems. The electrics and navigation system tended to overheat. The cockpit’s windows would mist up. And the aircraft’s range was limited to four hours before it needed to be refuelled. But there was also a more fundamental problem with the design of the controls.

“No matter what speed you were doing, the feedback on the control column felt the same,” says Duffey. “It was a danger handling the aircraft, without a doubt I think that led to one of the accidents.”

On 26 October 1952, Duffey was off-shift sipping red wine in Rome’s airport terminal after flying Comet G-ALYZ in from Beirut, Lebanon. Looking out of the window, he watched the plane begin its take-off for the flight to London.

“We saw the aircraft run off the end of the runway,” he recalls. “So we dashed out, got a jeep and drove out to where it was and it was just sitting there hissing – it ripped the belly tank out and there was fuel everywhere.”

As pilots we were becoming very concerned – Peter Duffey  

Incredibly, there was no fire and none of the crew or 35 passengers were injured. “What [the captain] had done was raise the nose too much on take-off; it had too much drag on the wings and didn’t get fully airborne,” Duffey says.

The pilot was blamed for the crash, but the incident also exposed an inherent flaw with the design. “The cause of the accident wasn’t only the wing but the lack of feedback on the controls that allowed you to pull-back as much as you wanted,” says Duffey. “It would never have happened if the test pilots had tested that aircraft properly.”

A few months later, on 13 March 1953, a similar problem occurred on take-off from Karachi. This time a Comet on a training flight, smashed into a stone bridge and burst into flames. All 11 crew members and technicians on board were killed. And then, in June, another plane was damaged at Dakar, Senegal in a similar incident.

“As pilots we were becoming very concerned,” says Duffey. “And we started to take a very active interest in what was going on.”

On 2 May 1953, 43 people died when a Comet crashed shortly after leaving Delhi in India. An investigation revealed the plane had broken apart after flying into extreme turbulence.

As a result of these incidents, new advisory take-off instructions were issued to pilots, adjustments were made to the wing design and future models of the plane would be fitted with weather radar.

But worse was to come.

“There were two fatal flaws with the aircraft,” says Hodgson. “First was the method of construction – the skin of the aircraft was made as thin as possible to save weight.”

“The Comet flew very high, and it needed to be pressurised so the passengers inside can breathe,” says Hodgson. “If you do that, it’s like taking a toy balloon and blowing it up and deflating it constantly – eventually it’s going to tear.”

Fishermen reported hearing multiple explosions before seeing burning debris plunge through the clouds  

The second problem concerned the rectangular windows. “If you have a square opening in a sheet of metal, like the skin of an airliner, and you stress it, the place where the crack is going to start is at the corner,” Hodgson explains.

On 10 January 1954, Comet G-ALYP took off from Rome and climbed into the clouds. During a radio call to report the weather, the transmission suddenly cut off. Below, fishermen reported hearing multiple explosions before seeing burning debris plunge through the clouds. All 29 passengers and six crew were killed.

All BOAC and Air France Comets were immediately grounded while the wreckage was recovered and investigations got underway. More than 50 modifications were ordered on the aircraft but investigators could not identify a single cause of the disaster.

“We had a series of meetings at Heathrow,” says BOAC pilot Duffey. “They said they were quite sure they’d covered what was going on.”

The meeting was asked to vote. “By a majority of one, we decided to go back into service,” he says. “I voted against because I felt the modifications had not adequately discovered the reason for the explosion.”

Unfortunately, he was proved right.

When Comet G-ALYY later exploded in mid-air on 8 April, all Comets around the world were grounded again.

“It must have been an earthquake through the industry, because everyone was looking to de Havilland and Britain as the pioneers of fast, high and comfortable air travel,” says Hodgson. “It was a huge mystery why these superb and futuristic aircraft were suddenly falling out of the sky.”

“I felt so aggrieved that they put it back into service,” says Duffey, “that I joined [the pilot union] Balpa on a more or less full time basis, determined to make sure we knew what was going on with aircraft we were operating.”

Over the equivalent of 9,000 flying hours, the water pressure in the aircraft fuselage was raised and lowered to simulate the conditions it would experience during flight  

A team of experts was assembled at the Royal Aircraft Establishment at Farnborough for an unprecedented investigation into the crashes. The process marked the birth of today’s global air accident investigation industry.

“It was obvious from the wreckage that the aircraft had explosively disintegrated in some way,” Hodgson says. “But you can’t just test an aircraft by making it do that again, so they immersed the aircraft in a very large tank of water and then started the stress tests and pressure tests.”

Over the equivalent of 9,000 flying hours, the water pressure in the aircraft fuselage was raised and lowered to simulate the conditions it would experience during flight. Then, after six weeks, the pressure suddenly dropped. The metal had cracked around one of the windows and the fuselage had blown open.

It was clear that the fuselage was too thin and the rectangular windows were a source of stress. The world’s first jet airliner had to be completely redesigned. With the Comet out of service, the rest of the airline industry suddenly had a chance to catch up.

“All the time, your competitors are looking over your shoulder at what you do,” says Hodgson. “They were all learning the lessons and coming up with designs that didn’t have the inherent flaws of the original de Havilland design.”

With the comet grounded, the aircraft that would transform the way we travel was taking shape in Seattle. Flown for the first time in July 1954, the Boeing 707 went into service in 1958. The company eventually built more than 1,000 of these iconic aircraft.

Back in the UK, de Havilland developed the Comet 2 and 3, before releasing the Comet 4 to the airlines by the end of 1958. Longer – comfortably carrying 92 passengers – stronger, more powerful and with much safer oval-shaped windows, it had a range of 2,500 miles, making it ideal for medium-haul flights.

It was beautiful to fly and land but it was too late – Peter Duffey  

“The Comet 4 was powerful, strong and reliable,” says Hugh Dibley, who began his flying career on the aircraft. “It was a lovely aircraft to fly in.”

Duffey agrees. “It was a super aircraft,” he says. “It was beautiful to fly and land but it was too late.”

Although the 707 was winning most of the major airline orders, BOAC, flying Comet 4s, still managed to achieve the first commercial transatlantic crossing in a jet airliner - twice. On 4 October 1958, Comet 4s left New York and Heathrow. Although the US bound flight had to stop to refuel in Newfoundland, the London flight made the journey non-stop in six hours and 11 minutes.

Comet 4s flew with BOAC until 1965 and with British airline Dan Air until 1980. The class was adapted into the hugely successful French Caravelle aircraft as well as the Nimrod reconnaissance plane, which continued to fly well into this century. The Comet 4 only finished its flying days in 1997.

Duffey, who had narrowly escaped two fatal Comet crashes, went on to become one of British Airways’ first Concorde pilots.

The British aircraft industry never fully recovered from the Comet’s dramatic failures. Today, the site of the de Havilland factory in Hatfield is an industrial park. The administrative offices are a police station, the entrance building a KFC, and the hangar where the Comet first flew from is a gym – the floor now covered in tennis courts.

The only surviving original Comet 1 is being renovated at the de Havilland Museum – a small volunteer-run collection of buildings and hangars in the countryside north of London. When BBC Future meets team leader Peter Kay, he’s working to re-install the ladies’ toilet.

It’s the only one in the world, and that’s why it’s so important to make sure it survives and people can see it – Peter Kay, Comet restoration team

“We’ve had to start from scratch internally,” he explains. “In places the aluminium of the fuselage had corroded so you could see holes through it.”

Over the past five years, the volunteers have lined the interior and have begun rebuilding the cabin and cockpit. “It’s the only one in the world, and that’s why it’s so important to make sure it survives and people can see it,” he says. “It’s amazing what they were doing 70 years ago, they were way ahead of their time.”

Although ultimately, Boeing triumphed in the race to produce a mass-market passenger jet and subsequent generations of aircraft have made flying safer, cheaper and widely available, the legacy of this British pioneer lives on.

“Today’s jet aircraft owe a huge amount to the Comet,” says Hodgson. “It taught the lessons that the other manufacturers learned and paved the way for modern safety and design.”

The Comet still looks like an aircraft from the future. Sitting on one of comfy upholstered seats of the First Class apartment, it is easy to imagine what it must have been like to fly in one of these beautiful aircraft high above the weather, maybe reading a magazine or sipping an iced drink.

As Hodgson says, “What’s not to like?”

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