Nat Geog_Comet Air Crash
Transcript
00:001954, and one of the world's first jet airliners takes off from Italy.
00:08The plane is the ultimate in high-speed luxury travel.
00:12But just 26 minutes into the flight,
00:15it explodes catastrophically.
00:1835 people are dead.
00:21The tragedy stuns a nation.
00:23A team of investigators must solve the mystery of why this state-of-the-art aircraft disintegrated on a routine flight.
00:33What they discover in the wreckage will cause a turning point in the history of aviation,
00:39and change passenger travel forever.
00:44Disasters don't just happen, they're a chain of critical events.
00:48Unravel the clues, and count down to those final seconds from disaster.
01:04Europe, 1954.
01:08Throughout the continent, there is a growing sense of optimism.
01:12As the nightmare of World War II begins to fade, former enemies forge new links.
01:17There's a spirit of enterprise.
01:20Civil aviation is booming, boosted by technological advances made during the conflict.
01:26In just two years, the number of airline passengers has nearly doubled.
01:329.30am, Sunday, January 10th, Rome Airport.
01:37Here, a dozen planes come and go every hour.
01:40On the tarmac stands Flight 781, en route from Singapore to London.
01:45The plane is a British-built de Havilland Comet.
01:48It's the marvel of its day, and the perfect symbol of the new technological age.
01:53The Comet is the world's first passenger jet, and it's halving journey times around the world.
02:01The pride of Britain sends a message of superiority to every aircraft manufacturer in the world.
02:07A dream comes true. At Hadfield Airport, the Comet, the world's first all-jet airliner.
02:14Begun three years ago, the airliner that makes every other passenger plane out of date will go into operation within 18 months.
02:21The revolutionary design is based on de Havilland's hard-won military expertise.
02:27The plane is powered by four ghost jet engines, and carries 42 passengers and crew.
02:33At up to 800 kilometres per hour, almost twice as fast as its nearest competitor.
02:39To help it achieve this staggering speed efficiently, it flies at a height of up to 12,000 metres, where the air is thinner.
02:47Until now, such performance was the preserve of military jet fighters.
02:52Twenty months after the launch, there are 17 of these aircraft in service.
02:57Nine of these aircraft are in service at the moment.
03:00Eight of these aircraft in service.
03:03Nine are owned by the British Overseas Airways Corporation, or BOAC, and among them is Flight 781.
03:129.40am. BOAC engineer, Jerry Bull, inspects the Comet's undercarriage.
03:19He checks for fuel leaks, tyre damage, and marks on the airframe.
03:25You're looking for this incidental damage. There was none, as far as I can recall, at that stage.
03:31So, my own thought at the time was walking on, we've got a clean aeroplane today.
03:37At 10am, Bull completes his final checks.
03:41The flight crew join him.
03:44The captain is Alan Gibson.
03:47At 31, he's one of BOAC's youngest pilots.
03:51Captain Gibson was a man of very good ability.
03:56Not a person who would panic about anything. He was, you know, confident.
04:01In Rome Airport Terminal, members of the new jet set enjoy breakfast.
04:07Also on the flight is renowned BBC reporter Chester Wilmot.
04:12He's returning home after covering a tour of Australia by the recently crowned British Queen.
04:21Chester is a devoted family man with three children.
04:27He's especially close to his ten-year-old daughter, Jane, who was born deaf.
04:32She is devoted to him, unaware that he's one of Britain's best-loved broadcasters.
04:39I just adored him.
04:42And I knew that he was busy, I knew he was on television, I knew he wrote books.
04:46But I don't think I even twigged how famous he was. He's just my dad.
04:5210.05am, and the last pieces of luggage are stored in the hold of flight 781.
05:02The plane will be flying today with 29 passengers and six crew members on board.
05:08One of the passengers is 23-year-old Bernard Butler.
05:12Bernard is an electrical engineer who's been working in Bahrain to save money for his forthcoming wedding.
05:20His fiancée is Pat Knight.
05:23They've been engaged for two years and plan to marry in a fortnight.
05:28I've made the bridesmaids' dresses, all the invitations have gone out,
05:33and we'd already received wedding presents.
05:37Everything was planned.
05:42Bernard is returning home with a surprise.
05:45He's picked out a dress for Pat to wear at their wedding.
05:52At 10.18am, all pre-flight checks are complete.
05:57Captain Gibson signs to confirm that everything is in order.
06:02Captain Gibson seemed very relaxed, also looking forward to getting home.
06:07Flight 781 is just one of five BOAC services from Rome to London today.
06:15An older generation of slower propeller-driven airliners make up the other flights.
06:21At 10.19am, a BOAC Argonaut, also bound for London, thunders down the runway.
06:28Captain Johnson is at the controls.
06:37At 10.30am, eleven minutes after the Argonaut's departure,
06:43the Comet taxes to the runway.
06:46Jerry Ball salutes goodbye.
06:58Air Traffic Control grants permission for take-off.
07:02One minute later, the high-tech plane takes to the air.
07:07It's a sunny day, and conditions for flying are perfect.
07:11The journey to London will be exactly two hours and thirty-seven minutes.
07:16The gleaming jet will arrive at London Airport a staggering two hours
07:21before the propeller-driven Argonaut.
07:24At 10.38am, Flight 781 climbs to an altitude of 1,000 feet.
07:29Flight 781 climbs to an altitude of 11,000 meters,
07:33twice as high as any other passenger aircraft.
07:39To achieve this, while allowing passengers to breathe comfortably,
07:43the engineer operates a pressurization system in the cockpit.
07:47As the Comet rises, the air pressure inside the cabin
07:51is maintained at the equivalent altitude of 2,500 meters,
07:56a level easily tolerated by the human body.
08:00But for some passengers, adapting to this new sensation is difficult.
08:08Soon, though, they acclimatize and settle back into their seats for the flight.
08:17What they cannot know is that they will never make it to London.
08:291954, and a state-of-the-art Comet jet airliner has taken off from Rome en route to London.
08:38On board are 29 passengers and six crew.
08:44As Flight 781 climbs, Captain Gibson receives a message from Captain Johnson in the slower Argonaut
08:51that took off a few minutes earlier.
08:54Each pilot uses the plane's call sign.
08:57Pow Jig for the Argonaut, Yoke Peter for the Comet.
09:13At 10.42 a.m., Captain Gibson contacts air traffic control.
09:18We've got a beam of the G-Sec you'd be confining at 23,000 feet.
09:22The plane will fly northwest over the Italian coastline, high above the Mediterranean Sea.
09:43At 10.51 a.m., Captain Gibson again radios the Argonaut.
09:47George Howjig for George Yoke Peter.
09:49George Yoke Peter from George Howjig.
09:52George Howjig, did you get my message?
10:04The message ends mid-sentence.
10:07Yoke Peter, Yoke Peter, come in, please.
10:10When Captain Johnson gets no response, he contacts Rome Airport.
10:15We've lost contact with the A7P. They just seem to have disappeared in the rain.
10:22At 10.56 a.m., the airport controller tries to contact the Comet.
10:27Without success.
10:29They fear something is terribly wrong.
10:34200 kilometers northwest, the Argonaut flies over the Mediterranean Sea.
10:39On the island of Elba, a group of Italian fishermen are repairing their nets.
10:44Among them is 33-year-old Luigi Pappi.
10:48As they work, something extraordinary happens.
10:55I felt a break in the air, and then there was a bang, and I heard a sound like thunder.
11:01But it was not like any thunder I'd ever heard before.
11:09They watch in amazement as flaming wreckage falls from the sky.
11:21At 11.15 a.m., air traffic control receives word that a plane has crashed into the sea off the island of Elba.
11:30It confirms their worst fears.
11:35Jerry Bull, here's the news.
11:38The senior engineer says,
11:40What's the bad news, Jerry?
11:42And I look at him, and he said,
11:44The Comet's down.
11:46It's an emptiness.
11:49You can't really describe it.
11:52It's just this numbness you get.
11:55And the next reaction, of course, is,
11:57Is this something I didn't do?
12:0112.00 p.m. Greenwich Mean Time.
12:04Chester Wilmot's family arrive at Heathrow Airport in West London to welcome the BBC reporter home.
12:16Pat Knight arrives with a friend after a four-hour journey from Nottingham.
12:20She's looking forward to seeing Bernard again.
12:231,200 kilometres away, a small flotilla of fishing boats heads off the coast of Elba towards the crash site.
12:33At first, we saw nothing.
12:36Then we saw a flock of seagulls which were pecking at something.
12:40So we headed straight for the seagulls.
12:43And that was where the plane had crashed.
12:53It's a harrowing scene.
12:56Bodies and debris float in the water.
13:02Among the carnage is a white wedding dress.
13:171.30 p.m.
13:191.30 p.m.
13:22Flight 781 is now over an hour late.
13:27Airport staff mark the plane as delayed.
13:31Jane Wilmot keeps a close eye on the arrivals board.
13:35Not all at once to keep me busy.
13:38So she's turned me off.
13:41Keep asking questions.
13:43Plane delays, plane delays.
13:45Jane suddenly notices that all reference to flight 781 has been removed.
13:54She decides to ask at the BOAC desk.
13:57Excuse me.
13:59Why is it not there on the board?
14:01Why has it gone?
14:03I can't give you that information at the moment, dear.
14:06We can't tell you.
14:08Go and get to your mother.
14:13Edith Wilmot is taken to a side room.
14:16Her children wait outside.
14:19They still believe their father's plane is delayed.
14:23How did...
14:25Oh, well.
14:28Do you think it happened?
14:31Minutes later, Edith returns visibly shocked and close to tears.
14:40Darling, this has been an accident.
14:43She tells her children that Chester is dead.
14:47Jane will never see her beloved father again.
14:54I just couldn't believe it was happening.
14:57But I'm very upset that I knew he was coming home for my birthday.
15:00And I kept on saying to myself, it wasn't his fault.
15:04He wasn't the pilot.
15:10The grim task of informing friends and relatives continues.
15:15Patricia Knight can scarcely believe what she hears.
15:20We were told it had come down.
15:21They didn't know whether there were bodies found or not.
15:28And there was nothing we could do.
15:33In an instant, Pat's hopes for the future are destroyed.
15:45In Italy, the fishermen begin the gruesome task of recovering bodies.
15:52It was a big shock.
15:57Every time we went near a corpse, we would shout,
16:00come over here, come over here.
16:02Because they seemed still alive.
16:05Their eyes were open.
16:07But when we got near, you could see they were dead.
16:14In total, 35 passengers and crew die on board Comet Flight 781.
16:22Fifteen bodies are recovered.
16:26There are no survivors.
16:38The dead are carried to a small chapel in Porto Azzurro.
16:46Local people say prayers.
16:49Children bring flowers.
16:57The horrific crash is headline news around the world.
17:02The question on everybody's lips is how could the most advanced airliner in aviation history just fall out of the sky?
17:15Was it a tragic accident?
17:18Or something more sinister?
17:25In 1954, the mysterious crash of the Comet dominates the thoughts of the British nation.
17:33Within hours of the crash, a team of experts working for BOAC begin a technical examination of the Comet fleet.
17:42They must discover if there's a flaw in the design or a manufacturing fault.
17:47Britain's position as the world leader in passenger jet travel depends upon it.
17:52The inquiry that follows will turn into one of the most complex and important in aviation history.
18:01Now, by going deep into the investigation, we can reveal the critical chain of events that caused the downing of Flight 781.
18:10Paul Withy is an aviation metallurgist.
18:14For six years, he studied the Comet investigation and is an expert on this turning point in aviation safety.
18:20Withy knows that with no established protocol for air crash investigation, it was an epic task.
18:27The difficulties they faced as an investigation team was to develop a whole new series of techniques for looking into a major air crash.
18:33And they had to really invent tests, invent methods of doing things as they went along.
18:38But Withy needs to be sure that this landmark case actually did get to the truth.
18:43Now, for the first time in half a century, he will re-examine the vital evidence.
18:48If he discovers their findings are wrong, it will rewrite the history of air crash investigation.
18:55From the beginning, the inquiry team are faced with an enormous challenge.
18:59In 1954, the investigation team had no black boxes.
19:03They had no flight data recorders.
19:05They had no way of understanding what was going on in the plane at the time of the accident.
19:10Their best clue, the aircraft itself, lies at the bottom of the Mediterranean Sea.
19:16Without the remains of the plane, the team know they must unravel the mystery with the flimsiest of evidence.
19:22With little to go on, the press speculate that sabotage might be the cause of the crash.
19:28These are the early years of the Cold War, and there are fears that subversive communists may be responsible.
19:34Sabotage. A bomb.
19:37And that came up fairly rapidly, you know, it was, it has to be.
19:41How did it happen?
19:43A bomb.
19:45A bomb.
19:46That came up fairly rapidly, you know, it was, it has to be.
19:50How did it happen?
19:52A bomb could have been hidden on board while the plane was taking on extra baggage.
19:58It's only a theory, but if true, it would at least eliminate doubts about the safety of the comet itself.
20:08With the pride and prosperity of a nation riding on the comet's success,
20:12success. A close eye is kept on the investigation from the very top. Winston Churchill himself.
20:23If saboteurs are responsible, the investigators know they must come up with hard evidence.
20:30They know that Flight 781 would have been flying at around 11,000 meters when something
20:35caused it to break up and fall from the sky. The Italian fishermen provide a few clues.
20:45I saw a huge ball of fire rotating and plunging into the sea. It left a huge, huge cloud of
20:55smoke. Captain Johnson, pilot of the Argonaut, deepens the mystery. The radio went dead in
21:02mid-sentence. Everything just cut out instantly. But it's the victims themselves that provide
21:09the biggest mystery. Within hours of the crash, Italian pathologist Dr. Antoni Fornari examines
21:17the bodies. Despite Fornari's considerable experience, he finds a pattern of injuries
21:23he has never seen before. The victims suffered broken limbs and damaged ribs, injuries sustained
21:31after death. But what confuses Fornari is that many of the bodies have fractured skulls,
21:38wounds he discovers that were sustained before death. He finds another puzzling clue. The
21:46lungs of almost all the victims are extensively damaged. Many have ruptured like an exploding
21:52balloon. To top it all, Fornari finds no evidence of a bomb blast. It's a strange perplexing
22:01picture and he's baffled. With so little evidence, the investigation hits a dead end. Concerned,
22:15Prime Minister Churchill summons his advisors and takes an unprecedented step. Churchill
22:21commands the Royal Navy to retrieve the wreckage of Flight 781 from the seabed. His orders
22:27are simple. Endeavour to locate and solve Comet. The task, however, is anything but
22:36simple. There has never been a salvage operation like it before. The wreckage lies at a depth
22:42of 120 metres and no one knows exactly where. Today, if an aircraft crashed in similar circumstances,
22:51the black box recorders would have transponders and would lead the investigators and the recovery
22:55teams to the spot where the aircraft was. The Navy didn't have that information. HMS
23:02Wrangler, an anti-submarine frigate, searches an area of 260 square kilometres. Three salvage
23:09vessels are on hand to help. They're equipped with the most up-to-date technology, including
23:15an underwater camera and a deep-seat observation chamber. But progress is delayed by bad weather.
23:25Then, on February 12th, 33 days after the crash, Navy experts identify the first piece
23:31of the Comet wreckage on the underwater camera. Divers descend to the sea floor. Over the
23:39next few weeks, small bits of debris are sent back to England for examination. Then comes
23:45a major find. A large section of the rear fuselage is located and brought to the surface.
23:56Meanwhile, in London, the Comet fleet sits idle. BOAC hemorrhages cash at the rate of
24:04£50,000 per week. With so much invested in the aircraft, pressure builds to get the planes
24:11back into the air. On March 23rd, ten weeks after the disaster, the British government
24:18give the airline the go-ahead to resume service. At London Airport, a Comet airliner about
24:24to leave for Johannesburg was taking out extra crew members. Press and television attend
24:29the relaunch. Everybody was in high spirits at the resumption of Comet flight. BOAC Chairman
24:35Sir Miles Thomas gives the Comet a public vote of confidence. We obviously wouldn't
24:39be flying the Comet with passengers in it on service were we not wholly satisfied that
24:44the conditions are acceptable for carrying passengers anywhere in the world. Wreckage
24:52from Flight 781 arrives in England piece by piece. Investigators identify and mark every
25:01fragment. In a hangar, carpenters build a wooden frame of the Comet aircraft. As the
25:07wreckage accumulates, they wire each piece onto this skeleton. Now, with the entire Comet
25:14fleet back in service, it's more important than ever to find the cause of the crash.
25:21The lives of hundreds of passengers depend on it. April 1954. While investigators urgently
25:34look for clues into the crash of Comet Flight 781, the British government give BOAC the
25:40go-ahead to relaunch their Comet fleet. It's a terrible mistake. At 6.32pm on April 8th,
25:50sixteen days after the resumption of flying, a Comet takes off from Rome bound for Egypt.
25:56Fourteen passengers and seven crew members are on board. Thirty-three minutes into the
26:02flight, the pilot reports that he's on course flying at 11,000 metres. It's his final message.
26:11A further 21 people are dead. The news sends shockwaves around the world. Barely a fortnight,
26:27after reassuring the public the Comet is safe to fly, BOAC's chairman publicly admits that
26:33he was wrong. Obviously, we cannot continue to carry the public in Comets until this is
26:41fully explained. Similarities between the two accidents are uncanny. Both planes were
26:49refuelled and checked at Rome by the same engineers, including Jerry Ball. You just
26:55can't accept that an airplane like this, again, it's gone down the same way and you've lost
27:01these people again. Both aircraft were flying at an altitude of around 10,000 metres. Both
27:07crashed into the sea shortly afterwards. It seems there must be a flaw in the aircraft
27:12itself. Churchill acts decisively. He appoints the Royal Aircraft Establishment, Britain's
27:20leading aeronautical research centre, to investigate. Heading the inquiry will be Sir Arnold Hall.
27:30Hall has an impressive reputation. He's a Cambridge scholar and one of the outstanding
27:34scientists of his generation. But even for a man as qualified as Hall, it's going to
27:39be a tall order. The second plane to crash rests under 1,000 metres of water and is impossible
27:47to retrieve. The hope is that if they can establish the cause of Flight 781's crash,
27:55it will explain why the second aircraft went down. Over the next four months, 781's wreckage
28:09is methodically pieced together at Sir Arnold Hall's headquarters in Farnborough. It's groundbreaking
28:16work. Never before on that scale had an aircraft been reassembled by anyone and the investigation
28:23team had to learn how to do it and develop the techniques and tools to reassemble a very
28:27badly damaged aircraft. As they examine each piece of debris, they find intriguing clues.
28:38Bits of carpet, pills from the first aid cabinet, a corner of a mirror from the toilet and scraps
28:45of passenger's luggage are all found wedged into the rear end of the fuselage under the
28:50root of the tail fin. It suggests an explosion at the front of the cabin that blasted personal
28:58belongings to the rear of the plane. The question is, how and where did the explosion start?
29:09As the wreckage begins to provide some clues, so too do the victims. Four of the bodies
29:16retrieved from the second crash are flown to Britain for post-mortem. The pathologist
29:23finds identical injuries to those of flight 781. Fractured skulls and ruptured lungs.
29:34Hall has a hunch. Could the entire plane have burst like a balloon? After all, the pressurised
29:42cabin designed to keep passengers comfortable would mean that the aluminium skin of the
29:47comet is highly stressed. Any structural failure and it might simply explode of its own accord.
29:57Such a violent decompression, as it's called, has never happened on a passenger plane before.
30:02But Hall and his team believe this could explain the terrible injuries. To test the theory,
30:08they stage a pioneering experiment. The team build a perspex model of the fuselage, one-tenth
30:16the actual size. The cabin includes 28 miniature seats with six dummies. The model is housed
30:25inside a pressure chamber. When the pressure in the fuselage is increased to eight and
30:30a quarter pounds, the equivalent of flying at 12,000 metres, the team deliberately rupture
30:35the model. A high-speed camera captures the results. The rapidly escaping air causes a
30:42tremendous release of energy. Seats tear apart and fly through the air. The dummies catapult
30:50vertically and smash their heads on the cabin roof. It's a graphic demonstration of a phenomenon
30:58experts like Paul Withy understand only too well.
31:20The pressure cabin exploding is the same as a 500-pound bomb going off inside the cabin.
31:25The experiment appears to explain how the victims of both flights sustained such horrifying
31:31head injuries. Not only that, the sudden change in pressure would cause the air inside the
31:37victims to expand rapidly, rupturing their lungs instantly. If explosive decompression
31:45can explain what happened to both planes, the team must discover exactly what caused
31:51the weakness in the structure of the fuselage. But a failure in the aluminium skin seems
31:58implausible. The manufacturer's own tests show the natural life expectancy of the fuselage
32:04is over 10,000 flights, many more than the number flown by the two crashed planes. Nevertheless,
32:12Sir Arnold is not a man to leave any stone unturned. He decides to put the entire airframe
32:18to the test. Before testing begins, the team look closely at the comet design. They discover
32:27that to withstand the stress caused by repeated pressurizations, the skin of the aircraft
32:33must be immensely strong, but it must also be extremely light. In order to achieve this,
32:41de Havilland developed a lightweight aluminium alloy skin, just over half a millimetre thick.
32:51The comet's skin thickness was as thin as the designers dared go to withstand the cabin
32:56pressurization, and it was fixed by how little they thought they could get away with. Sir
33:01Arnold devises a test to assess the strength of the plane's fuselage. The experiment is
33:08on a completely different scale to anything they have attempted before. It requires the
33:13construction of a massive water tank, measuring 34 metres long by 7 metres wide and 5 metres
33:21deep. Working non-stop, it takes a team of engineers six weeks to complete. The team
33:29at the Royal Aircraft Establishment are working really hard. They're working 24 hours a day,
33:33they're working shifts, they're sleeping on site. They are a very dedicated team. By
33:38May 29th, it's ready. The engines and cabin upholstery of a comet are stripped out. The
33:45empty plane is gently manoeuvred into the water tank, with the wings protruding on either
33:50side. Engineers fill the tank and the plane with water. When they are both full, they
33:58force more water into the plane, pressurizing it as if it were flying. After five minutes,
34:08engineers reduce the pressure. Each test puts the same amount of strain into the aircraft
34:14as a single flight at 12,000 metres. Sir Arnold plans to test the fuselage to destruction.
34:22It could take up to five months. The experiment runs 24-7. Using 1950s technology, it's a
34:32gruelling task. Today we wouldn't do a water tank test. We'd actually use computer modelling
34:38and computer simulation to understand how the aircraft would behave. As the tests continue,
34:43there are other lines of enquiry. In mid-June, five months after the crash of Flight 781,
34:50the team assembled two-thirds of the fuselage onto the wooden frame. Half a wing lies on
34:56the floor. It's now clear from the tears in the metal that the aircraft has indeed decompressed
35:04violently and blown apart at the seams. By following the fractures back to where they
35:11started, they think the initial failure was probably at the front of the fuselage, somewhere
35:17between the cabin and the cockpit. It seems as if the tail and rear fuselage then came
35:22away from the main cabin. The rear wing structure followed, and then the outer wingtips. The
35:29cockpit broke away as the plane plummeted to earth, and finally fuel from the wings set
35:35the debris ablaze. But the exact cause of this tragedy is still a mystery. Then, on June
35:4324th, Sir Arnold Hall gets a call that changes everything. The team running the water tank
35:49test has had a major breakthrough. Less than a month after testing began, after the equivalent
36:04of just 3,000 flights, the comet fuselage ruptures. Engineers immediately drain the
36:11tank, and Sir Arnold Hall inspects the damage. There is a massive tear in the aircraft's
36:18skin, two metres long and one metre deep. The tear follows the line of the plane's windows
36:25and doors. It's a shocking but vital turning point. They have uncovered a major weakness
36:33in the structure of the comet. The entire fleet seems to be fatally flawed. I think
36:40everybody was thunderstruck. De Havilland certainly was thunderstruck because they didn't
36:43expect a comet airframe to fail so soon in its life. But what triggered such a dramatic
36:49failure? There's one prime suspect, a phenomenon known as metal fatigue. It's something Paul
36:57Withey knows well. This is a piece of aluminium sheet similar to that which was used on the
37:04comet's skin, but much thinner. One cycle of load isn't going to fail it at all. But
37:08if I repeatedly load it, like this... Fatigue is caused when a metal is repeatedly flexed
37:15one way and then the other. There you can just see it's about three or four millimetres
37:20across the sheet. After a while, minute cracks start to form. Cracks growing further and
37:27further across the sample. The cracks steadily increase in size, and eventually the part
37:34fails. But there are two problems with this explanation. Metal fatigue leaves a tell-tale
37:44microscopic pattern on the surface of the metal. Although in the 1950s, the technology
37:51for detecting this pattern is infancy. None of the parts reclaimed from the sea seem to
37:57show any sign of it. Secondly, before the comet went into service, the manufacturers
38:04did extensive fatigue tests to find out how the fuselage would behave under repeated pressurisations.
38:11It passed with flying colours. Sir Arnold knows he must come up with hard evidence to
38:16prove the theory. He must find a part of Flight 781 that shows signs of the fatigue. The piece
38:23of evidence that Sir Arnold needed above all other was that source of fatigue crack growth
38:29that he knew was there in the airframe somewhere. A single piece of wreckage is all that's needed
38:35to validate the entire investigation. But this crucial evidence still lies at the bottom
38:40of the Mediterranean Sea.
38:48It's 1954, and investigator Sir Arnold Hall believes that the cause of the two comet crashes
38:54is a rupture in the plane's lightweight skin. After a unique pressure test on the comet's
39:01cabin, the team examine the two metre split that has ripped along the side of the fuselage.
39:10They make some frightening discoveries. By tracing the tear back, they find it starts
39:16at the forward escape hatch. This is not surprising. Stress to the aircraft should be evenly spread
39:24throughout the fuselage. But when a door or window is cut into the plane, it weakens the
39:30structure, and the stress concentrates around the weakened areas. To investigate further,
39:38they rig another aircraft with strain gauges designed to measure stress in the airframe.
39:44The results are shocking. During flight, the stress to the skin around the plane's windows
39:49and doors reaches 70% of its total strength, four times greater than the rest of the aircraft's
39:55skin. This is dangerously high, and twice what the designers intended. Then the team
40:01discover an even more worrying detail. The supports around the windows are riveted, not
40:07glued as designed. The problem is, the rivets are punched into the metal, not drilled. This
40:13technique creates tiny manufacturing defects, which with repeated flying, can turn into
40:19fatigue cracks. The presence of manufacturing cracks in a highly stressed area meant that
40:25you were highly likely to suffer from fatigue failure. Sir Arnold and his team know they're
40:30getting close, but they have not yet conclusively solved the mystery. They've found no trace
40:35of metal fatigue on any of the wreckage from flight 781. Then on August 12th, seven months
40:42after flight 781 crashed, an Italian trawler snags a large piece of wreckage. It turns
40:49out to be a section of the roof from 781's fuselage. The piece includes two small windows
40:56built for sending and receiving radio signals. Sir Arnold Hall and his team inspect the wreckage
41:06at Farnborough, and immediately find what they're looking for. A rivet hole in the corner
41:13of one of the windows shows a tiny crack. When they put the piece together with the
41:18rest of the wreckage, they find that all the cracks run back to this point. They have
41:30their missing clue. On Tuesday, October 19th, after six months of grueling work, Sir Arnold
41:38Hall presents his findings to a court of inquiry. But one detail fascinates Withy. In 1954, the
41:55techniques for analysing metal fatigue were crude. The final piece of wreckage was examined
42:00with an ordinary microscope, and the team relied on experience to make their conclusion.
42:07Today, London Science Museum safeguards the crucial piece of wreckage. Paul Withy goes
42:14to see the historic item for himself. No one has ever used modern methods to re-examine
42:21the evidence. Using 21st century know-how, Withy wants to look again at the wreckage
42:27and check that Sir Arnold got it right. In order to preserve the damaged section, it
42:35has been mounted onto a plate. Running from a rivet hole is the crack which, it's believed,
42:43started the catastrophe. To examine the damage in more detail, Withy makes an impression
42:54of the crucial area using a silicon-based putty. Then, at Imperial College London, Sir
43:05Arnold uses an electron microscope to examine the sample. Magnifying the crack about 200
43:13times, Withy shows what Sir Arnold would have seen. This is a fatigue crack we saw on the
43:20comet's skin, and Sir Arnold Hall and his team could see that using their techniques
43:24of the day. But zooming in further to 800 times, Withy can see detail that Sir Arnold
43:30never could. He finds a tiny manufacturing defect, probably formed when the rivet was
43:36punched into the metal. And it was that manufacturing defect that caused this fatigue crack to grow.
43:42And it's this image here that shows that Sir Arnold Hall and his team were right. It vindicates
43:47them in seeing that it was a fatigue crack which then grew to failure. 52 years after
43:52the most groundbreaking and innovative investigation in aviation history, Paul Withy has conclusive
43:59proof that Sir Arnold Hall's results are absolutely right. Now, by rewinding the events
44:07leading up to that fateful crash, and by following the evidence uncovered during the investigation,
44:12we reveal how Flight 781 was downed. 10.31am, January 10th, 1954. 26 minutes to disaster.
44:25Flight 781 takes off from Rome Airport. The plane is designed with an exceptionally thin
44:32aluminium skin. Rivets punched into the aircraft during construction create microscopic manufacturing
44:40defects. On each flight, the pressurisation system puts enormous strain on the fuselage,
44:47causing stress to the skin, especially around the windows and doors. Repeated pressurisations
44:56turn the manufacturing defects into fatigue cracks that get bigger with every flight.
45:0519 minutes to disaster. Flight 781 climbs to 11,000 metres. As it ascends, the pressure
45:13increases, and the aircraft's skin becomes more stressed. At 10.51am, the comet's pilot,
45:22Captain Gibson, sends a radio message. Five seconds to disaster. A fatigue crack reaches
45:29two centimetres in length, and the aircraft's skin rips apart.
45:34At 10.57am, the shattered pieces of Flight 781 fall from the sky.
45:43Thirty-five people are dead.
45:53On the island of Elba lies a memorial to those who lost their lives.
45:59On the island of Elba lies a memorial to those who lost their lives over 50 years ago.
46:07The pain of the tragedy will never be forgotten, but the scientific understanding gained during
46:13the investigation is comfort to some.
46:17I know it gave my mother a great deal of comfort for the test they did following the comet crash.
46:25They saved people's lives later.
46:29Four years after the crash, the comet did fly again, but it never achieved the commercial
46:35success it once promised. In the interim, American company Boeing developed their own
46:41passenger jet and became the dominant force in the world of aviation. The de Havilland
46:46Aircraft Company went into decline and were eventually taken over. Passenger air travel
46:53had changed forever.