This special looked at accidents and incidents where pressurization failure or explosive decompression played a part.
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00:00Every passenger jet is a travelling life support system,
00:03carrying inside it the highly pressurized oxygen that keeps us alive.
00:08If it ever escapes, a simple flight becomes a living nightmare.
00:15United 8-11.
00:17There was nothing in front of us, or to the side of us.
00:19The whole side of the plane was gone.
00:22Aloha 243.
00:26Everything was gone. It was being sucked out of the plane.
00:30British Airways 5390.
00:33I'll never forget, his face was hit in the side screen.
00:37But he didn't blink.
00:39Made it! He made it! He made it!
00:41Declaring an emergency!
00:44Sometimes it takes a terrible accident to expose hidden dangers
00:49and change the way airplanes are built.
00:51Unfortunately, we wait until we have enough bodies.
00:54Too many of the changes have been, in effect, written in blood.
01:01Made it! Made it!
01:23This is the assembly plant for the Airbus A320.
01:27After the Boeing 737, it's the most popular jet plane ever built.
01:33Almost 2,000 of them are flying for airlines around the globe.
01:37It's safe and dependable, the airline equivalent of a minivan.
01:43The aluminium skin on the top of an A320 is less than 2 mm thick,
01:48about as thick as a coin.
01:51But this slender piece of metal helps keep passengers alive.
02:00Because the skies aren't nearly as friendly as they seem.
02:06Most people take aviation absolutely for granted.
02:10The difference between being on a commercial airliner at 35,000 feet
02:14and being in a space capsule in orbit is really not a big difference.
02:18They're both life support systems.
02:21The reality is it's a hostile environment.
02:24The reality is it's 50 degrees below zero outside.
02:27The reality is that jet stream or that air stream out there
02:29would kill you almost immediately.
02:35It's not natural for people to travel through this killer atmosphere.
02:41But every day, millions of us fly easily some 3,000 metres above sea level.
02:483,000 metres higher than the top of Mount Everest.
02:52All our life support that's natural for us is down here at the bottom of this sea of air.
02:57And if we swim up too high, however we get there, if we're not protected, we can't live.
03:09But taking oxygen with us up to 11,000 metres is potentially dangerous.
03:18The air inside an airplane is pressurised so passengers can breathe easily.
03:23As planes climb, the pressure outside decreases.
03:27The tightly packed air in the cabin begins exerting tremendous pressure on the fuselage.
03:34On an average jetliner, it means that every square metre of the fuselage
03:38must support more than 5,000 kilograms of force.
03:49And on almost every flight, the fuselage wins the battle.
03:56But only because airplane designers have learned tragic lessons.
04:02We have concentrated in the past on changing things,
04:05but unfortunately we wait until we have enough bodies.
04:11In the 1950s, a series of shocking accidents triggered changes that are still seen today.
04:18The comet has blazed new trails, achieving new speeds, setting a new standard.
04:25The passenger jet era began in the 1950s with the introduction of the de Havilland comet.
04:32For the first time, jet engines were being used to push commercial planes higher than ever before.
04:40What Great Britain had at stake with the comet was enormous.
04:45They wanted to really declare their place in civil aviation
04:51by having the first successful jet transport aircraft.
04:58But less than two years after its maiden flight,
05:01the glittering jewel of British aviation disintegrated in mid-air.
05:06It would have been horrible. It would have been a horrible situation,
05:10but mercifully it would have been quick.
05:14What they had found with the bodies that they had recovered
05:17was the massive decompression, of course,
05:19caused the air inside your lungs to burst your lungs.
05:22At the same time, the outrush of air would tear you from your seat
05:27and many of these people would actually smash their heads against the ground.
05:31Three months later, another comet ripped apart in flight.
05:35Officials fear that every single comet could be a flying time bomb.
05:40The entire fleet is grounded.
05:44The design of the comet was actually a very sound design.
05:48There was only one thing that they didn't do, and it's because nobody knew.
05:52Unknown to engineers, there was a deadly flaw in the comet's basic design.
05:59To find the jet's fatal weakness, investigators built a massive water tank.
06:04They immersed a stripped-down comet.
06:07The pressure in the tank was increased and decreased,
06:10simulating the strains of flight.
06:14The jet was so heavily compressed,
06:16the pressure in the tank was increased and decreased,
06:19simulating the strains of flight.
06:23The experiment ran 24 hours a day, seven days a week.
06:30After the equivalent of some 3,000 flights,
06:33the comet's Achilles' heel revealed itself, its square windows.
06:40You have a rapid change of direction in the shape,
06:43essentially a corner, you have a high stress concentration.
06:47It gave rise to a fatigue crack,
06:49which then travelled rapidly through the rest of the structure,
06:52causing a massive decompression.
06:55The most advanced passenger jet in the world had succumbed to metal fatigue.
07:00The fuselage simply could not handle the force of the air inside, pressing out.
07:06The airplane, with all that force behind it, suddenly unzipped itself.
07:11Every plane that's built today is safer
07:14because of the disaster that struck the comet.
07:19Like other passenger planes, the windows on the A320 are rounded,
07:23so that pressure doesn't build up around the corners.
07:28Perhaps even more importantly,
07:30extra rivets reinforce the skin of today's planes
07:33to contain cracks that might still be visible.
07:36It's designed to go to that first row of rivets and absolutely be stopped.
07:40It's a healthy structure, it can never unzip itself.
07:47But 34 years after the comet crash,
07:50aircraft manufacturers were faced with another tragic disaster.
07:58The A320 was the first of its kind.
08:01It was a rather tragic disaster.
08:06The extra rivets that were supposed to save lives
08:09failed to withstand the relentless power of air pressure on metal.
08:16One of the fellows that I knew at the FAA, he said,
08:19you know, the day after this accident,
08:21I had to throw away most of what I knew about metallurgy and start over.
08:32At this airbus factory in Toulouse, France,
08:35A320s roll out at about the rate of one every working day.
08:41Titanium rivets, lightweight and extremely tough,
08:44hold the fuselage together.
08:463,000 are used to join the separate sections.
08:51Another 3,000 can be found on each wing.
08:55Without them, the fuselage couldn't contain the pressurised air
08:59that's forced inside during flight.
09:02But even these rivets aren't foolproof.
09:09April 28, 1988, Aloha Airlines Flight 243
09:14is travelling from Hilo Airport on the Big Island to Honolulu.
09:20With this island hop, Aloha 243 is making its ninth flight of the day,
09:25a normal schedule for the planes of Aloha.
09:29Protected within the jet, passengers give little thought
09:32to the fact that the cabin is filled with pressurised oxygen.
09:36It's constantly pushing against the fuselage,
09:39trying to escape into the surrounding atmosphere.
09:43In the cabin, the pressure is kept at a constant level,
09:46so passengers feel like they've never left the ground.
09:49But as a plane rises to its cruising altitude,
09:52the air pressure outside the cabin is dangerously low.
09:55Well, what we do is extract air from the engines
10:00and use that to pressurise the airplane.
10:03And what we can do then is control the pressure inside by a series of valves.
10:10The air moving through the cabin creates constant pressure on the jet's fuselage,
10:14keeping it inflated like a balloon.
10:17Every modern jet is built to withstand this pressure.
10:20There's an internal structure to a modern all-metal airplane.
10:23The skin without the structure would collapse easily.
10:26It would buckle easily. It would be sort of like a paper bag
10:30without any structure inside to hold it.
10:34If you remove the skin of a passenger jet,
10:36you'll find hoop-shaped bulkheads and formers
10:39supporting the width of the aircraft.
10:42Stringers run the length of the plane.
10:44They all help support the fuselage.
10:46And the cabin needs all the help it can get,
10:48because as the plane gains altitude,
10:50that pressurised oxygen inside the plane is pushing against every square centimetre.
10:59On this day in April 1988,
11:02passengers are about to learn what happens when that air suddenly escapes.
11:08I saw a brilliant flash of light and boom.
11:13Everything was going, was being sucked out of the plane.
11:17Aloha Airlines 243 has just suffered
11:20what experts call an explosive decompression.
11:23This is the first time in the history of aviation
11:26that an aircraft has been sucked out of the plane.
11:29It's the first time in the history of aviation
11:32that an aircraft has been sucked out of the plane.
11:35Explosive decompression.
11:37The air inside the plane that makes jet flight possible
11:40escapes in a sudden horrifying moment.
11:4335 square metres of the fuselage are gone.
11:48Just imagine the scene up there.
11:49The top of the airplane broken off.
11:51You now have 300 mile an hour winds blowing into that cabin.
11:54That's three times hurricane force winds.
11:57Those people were dressed for Hawaii in the springtime,
11:59not minus 50 degree temperatures.
12:01Any period of time at 24,000 feet and those people will die.
12:05We have to get down.
12:07Captain Bob Schornsteiner begins an emergency descent
12:10dropping 20 metres a second.
12:12The stress on the damaged craft threatens to tear it apart.
12:17The woman that was sitting next to me and her husband,
12:20he was on the other side in the next row up and she was next to me
12:23and they were reaching their hands out
12:25and they were trying to touch fingers to say goodbye.
12:28Against incredible odds,
12:30the flight crew land their bruised and battered airplane.
12:39Even with this explosive decompression,
12:42there's only one death on Aloha Flight 243.
12:45A flight attendant who was pulled out of the plane.
12:54Jim Wildey investigates the crash
12:56for the National Transportation Safety Board.
13:01In his laboratory, Wildey makes a disturbing discovery.
13:05Running through some of the pieces of the plane's fuselage,
13:08he finds a series of hairline cracks.
13:11They're right beside the holes created by rivets
13:14and barely visible to the naked eye.
13:16But they're classic signs of metal fatigue.
13:19Metal fatigue is something that sounds exotic
13:23but it really is easy to understand.
13:26Any piece of metal has a certain breaking point.
13:29All of us have tried to open a tin can
13:31and not quite gotten the opener all the way around.
13:34We work it back and forth until that last portion breaks.
13:37You just demonstrated metal fatigue.
13:41A plane isn't a rock-solid tube.
13:44To maintain the pressure passengers need to enjoy a flight,
13:47it's designed to be much more flexible.
13:50The fuselage of the airplane is actually breathing.
13:53It expands and contracts depending on altitude.
13:56When it's on the ground, it's in a contracted status.
13:59When it's at altitude, 24,000 feet, the fuselage expands.
14:04If you could stand at the back of a 250-foot long jetliner
14:08and just sight along that fuselage,
14:10you'd see it begin to puff up a little bit.
14:13And as a plane lands, the pressure differential
14:16between the inside and the outside of the plane disappears.
14:20The fuselage returns to normal.
14:22So the airplane is constantly cycling.
14:24That's pressurization.
14:26That will weaken the structure over a long period of time.
14:31Records show that the Aloha jet was 19 years old.
14:35737s are designed for a 20-year service life
14:39and are recommended 75,000 flights.
14:42But as investigators take a closer look,
14:45they discover that the Aloha jet
14:47had logged an astonishing 89,000 separate flights.
14:51The short hops between the Hawaiian islands
14:54meant that the planes in the Aloha fleet
14:56went through more pressurization cycles than any other aircraft.
15:00You saw something as you got on this airplane. What did you see?
15:04Investigator Jim Wildey gets a lead
15:06when he interviews one of the Aloha passengers.
15:09She says she saw a small crack in the fuselage
15:12just to the right of the door.
15:14The witness saw cracking in this area
15:17and we found fatigue cracking back in here.
15:20So this is the line where the fatigue cracking joined up.
15:23One piece came down this way and folded off
15:26and the other piece went across the top and came off to the right side.
15:30But something doesn't make sense.
15:33The Aloha jet lost 35 square meters of its fuselage.
15:37In the years after the comet disaster,
15:40Boeing and other companies had designed a safety feature
15:43that should have kept any tearing to an absolute minimum.
15:47Inside the fuselage of every 737,
15:50Boeing has installed a series of tear straps.
15:53If any kind of tear develops in the fuselage,
15:56it should only run as far as the next tear strap,
15:59never more than 13 centimeters away,
16:02before shooting off at a 90 degree angle.
16:05This would have prevented the sort of catastrophic disintegration
16:08that ripped apart the comet.
16:11The purpose of the tear strip is to confine any kind of rip or tear
16:14in the fuselage skin to a 10-inch square, basically.
16:17The 10-inch square allows a controlled decompression
16:20and confines any structural damage to a very small area.
16:26But for Aloha 243, the tear straps did not contain the rupture
16:29caused by the metal fatigue.
16:32The NTSB believes there were so many cracks in the fuselage
16:35that they eventually joined together,
16:38tearing an enormous hole in the plane.
16:42But jets aren't held together by rivets alone.
16:45The comet disaster had also highlighted
16:48the need to reinforce the fuselage.
16:51The skin of an airplane is built from separate panels,
16:54which overlap.
16:57These panels are bonded together by a powerful adhesive known as epoxy.
17:00As the epoxy hardens,
17:03the panels are locked together by rivets.
17:06And during his investigation on the Aloha fuselage,
17:09Jim Wildey finds discoloration inside some of the overlapping joints.
17:15You can see now where the dark material is the epoxy
17:18that was used to bond the two layers of the lap joint together.
17:23The white material you see here is corrosion damage
17:26of the aluminum fuselage skin.
17:29The Hawaiian climate is great for tourists,
17:32but it's tough on airplanes.
17:35The ocean air is humid and heavy with salt.
17:38It can corrode even industrial epoxy.
17:41Investigators learned that Boeing,
17:44the company that built Aloha 243,
17:47had issued numerous written warnings about the epoxy.
17:50If it isn't applied at the right temperature,
17:53if the panels have moisture or dirt on them,
17:56the bonding can fail.
17:59Boeing recommended regular detailed inspections.
18:02But workers at Aloha didn't report any problems with the epoxy.
18:05They either never saw the compromised epoxy,
18:08or if they did, it wasn't repaired.
18:13The stress that's trying to pull one skin away from the other skin piece,
18:16the stresses would go through the bonding and not through the rivets.
18:19Of course, as this thing becomes dis-bonded,
18:22now the rivets themselves are loaded,
18:25and especially this top row of rivets,
18:28and this is the row of rivets, we think, that had the fatigue cracking in it.
18:32These cracks go unrepaired,
18:35and now you have an airplane that is a ticking time bomb.
18:38The fuselage on Aloha 243
18:41was seriously compromised by several factors.
18:44Poor maintenance, the age of the aircraft,
18:47and by the heavy tours of duty.
18:50Since 1988, we have come light years in understanding this,
18:53and we no longer leave ourselves the tolerance
18:56that used to be left to airlines to just go out
18:59and take a look at the airplane and sign it off.
19:06The Aloha accident was another step
19:09towards making passenger jets safer.
19:14It's important to always learn from your mistakes.
19:17It's important to learn lessons from that,
19:20and that has been the case with aeronautical engineering.
19:24The Aloha story was a brutal lesson
19:27in the dangers of metal fatigue,
19:30but it wasn't the last example of the power of cabin pressure.
19:37Two years later,
19:40the industry would get another terrifying reminder.
19:46Ladies and gentlemen, this is your captain speaking.
19:49My name is Tim Lancaster.
19:52Welcome aboard this British Airways flight to Malaga.
19:56British Airways flight 5390
19:59is leaving Birmingham, England, for Spain.
20:0287 people are on board.
20:0580 knots.
20:13Two minutes into the climb,
20:16the flight crew switch on the autopilot.
20:19Captain Tim Lancaster takes off his shoulder straps.
20:23Now I went into the flight deck
20:26to ask Tim and Alistair
20:29what they would like to drink.
20:32Any gentlemen like a tea? Please, the usual.
20:35Minutes later, at 5,200 metres,
20:38the plane is very close to its assigned altitude.
20:41And then, like a cork out of a champagne bottle,
20:44the windshield bursts from its frame.
20:53Captain Tim Lancaster is sucked out of his seat
20:56and is pinned to the fuselage by blistering winds
20:59roaring close to 550 kilometres an hour.
21:02The temperature is minus 17 degrees centigrade
21:05and there's very little oxygen.
21:08Co-pilot Alistair Atchison is alone at the controls.
21:13Ordinarily, cockpit windows cannot budge from their frames.
21:16The force of the air as the plane soars up
21:19pushes the windshield onto the plane.
21:22But on flight 5390, something has gone terribly wrong.
21:26Flight attendant Nigel Ogden rushes in to help.
21:29And I looked in.
21:32The flight deck door was resting on the controls
21:35and all I could see was Tim out the window.
21:42I just couldn't believe it.
21:46I just grabbed him before he went out completely.
21:50Other flight attendants do what they can.
21:53Co-pilot Alistair Atchison reduces speed and descends quickly.
21:57But as he slows the plane down,
22:00the drop in wind pressure lets the captain slide around
22:03on the side of the plane.
22:10All I remember is Tim's arms flailing out.
22:13His arms seemed about six foot long.
22:16And I'll never forget that. His eyes were wide open.
22:19I mean, his face was hitting the side of the side screen.
22:24But he didn't blink.
22:27And I thought to myself and I said to John,
22:31I said, I think he's dead. I think he's dead.
22:38Just 35 minutes after taking off,
22:41Atchison gets his jet safely back on the ground.
22:57But the most unbelievable chapter of this entire story
23:00is the fact that Captain Tim Lancaster survives his incredible ordeal.
23:06I remember watching the windscreen move away from me.
23:10It moved away from the aircraft and then it had gone like a bullet.
23:13It disappeared into the distance.
23:17And I was very conscious of going upwards.
23:20And, well, the whole thing became completely surreal then, as it would.
23:24And I was aware of being outside of the airplane.
23:27I can remember seeing the tail of the aircraft.
23:29I can remember the engines going round.
23:31And then I don't remember much more.
23:35Tim Lancaster was pinned to the outside of the plane for over 20 minutes.
23:39His injuries were surprisingly minor.
23:42Bone fractures in his right arm and wrist, frostbite and shock.
23:48Within five months, Tim Lancaster was flying again.
23:57In the immediate aftermath, investigators have very little to go on.
24:02The windscreen was missing. There was a certain amount of blood around.
24:06There were some minor dents and scrapes on the fuselage,
24:09as you'd expect if the window had gone past.
24:12And, really, that was about it, apart from a lot of paper scattered around inside.
24:18The maintenance log is recovered from the plane.
24:21Stuart Culling learns the windscreen had been replaced just hours before take-off.
24:27Everything OK? Fine.
24:29Should just come out of maintenance, by the look of it.
24:32Nothing much, though. Just changed the windscreen.
24:35I wanted to find out exactly what had happened to the aircraft before it took off.
24:40Early in the investigation, the missing windscreen is found.
24:44It contains a curious piece of evidence.
24:47There were something like 30 bolts found with it,
24:50most of which were one size short in diameter,
24:54one size too small in diameter.
24:56On many planes, windscreens are fitted from inside the cockpit.
25:00Internal cabin pressure pushes against them, keeping them in place.
25:04But on the BAC-111, the windscreen is bolted from the outside.
25:09The pressurised oxygen inside the jet pushes out against the windscreen.
25:14The bolts must resist this pressure.
25:17There are enough of them there that they simply can't pull out of the structure.
25:21But of course, if you then violate the very premise of that by putting the wrong bolts on,
25:25all bets are off. You're now a test pilot.
25:28During his interview with the ground engineer who repaired the plane,
25:31Culling gets a major break.
25:34One thing that came out was that he said,
25:36oh, the old bolts went into a waste bin in the hangar where he did the job,
25:40and they may still be there.
25:42So he rushed across to the waste bin and found something like 80 discarded bolts.
25:46The old bolts are the proper size.
25:48Why were smaller bolts used to replace them?
25:51And these are the ones you checked against the new ones?
25:54That's right. From the carousel.
25:56It was really excellent evidence. Gold, as far as I was concerned.
26:01Instead of using the old bolts to put the new window on,
26:04the ground engineer decided to replace them.
26:08He did not check the parts catalogue to verify which bolt he needed for the job.
26:18Morning.
26:21The bolts he chose seemed the same,
26:23but in fact were just over half a millimetre smaller.
26:27They were too thin to do the job.
26:35Early in the morning, working against the side of a hangar,
26:39the engineer couldn't tell the difference.
26:44Hours later, the window gave way.
26:48Shh!
26:55Faced with a challenge they weren't trained for,
26:58the crew still managed to pull their plane back from the brink.
27:03But the massive pressure inside an airplane doesn't need bad maintenance to rip a jet apart.
27:12That pressure can also find a tiny flaw somewhere in the design
27:16and cause a nightmare in the sky.
27:30The Airbus A320.
27:33One of the most popular passenger jets in the sky.
27:38Every day around the world, thousands of passengers board this plane.
27:44When they do, they walk through what would seem to be an obvious weak spot in the fuselage.
27:50The door.
27:54Any hole in the fuselage is a potential danger.
27:58So engineers designed passenger doors that can't be opened in flight.
28:06It is virtually impossible, I don't use that word very easily,
28:10but it is impossible for a passenger to open a plug-type door in flight.
28:14Passenger doors are plug-type doors.
28:18They're built to be slightly larger than their frames.
28:22When a plane takes off and pressurises, the atmosphere inside the aircraft seals the door shut.
28:28That door probably has 10,000 or more pounds of pressure holding it firmly in place in that door frame,
28:35and you have to pull it out of that door frame to get it open.
28:38But not all doors on an airplane are built the same.
28:41Even designs that seem flawless on paper can rip apart in the real world.
28:49February the 24th, 1989. Honolulu Airport.
28:54United Airlines 811 is bound for Auckland, New Zealand.
28:59Expected flying time, nine and a half hours.
29:03There are 355 people on board, plus a full load of cargo.
29:09The doors close on time, and the plane leaves the gate just after 1.30 in the morning.
29:19Tell him I can handle 33.
29:23We did notice that there were thunderstorms 100 miles south, right on course,
29:28which was rather unusual for that time of night.
29:32So I left the seatbelt sign on.
29:35Captain Cronin's decision to keep that sign on will save lives.
29:42As the 747 climbs past 7,000 metres,
29:46passengers sitting just above and behind the cargo door begin to hear a strange noise.
29:52Kind of a grinding noise.
29:55I heard a, like a thud.
30:00What the hell?
30:01In the next nanosecond, it was pure, unadulterated pandemonium.
30:17The next thing I knew, I found myself on the floor of the plane.
30:21The next thing I knew, I found myself on the stairwell,
30:25hanging on to the rungs, and I immediately knew it was an explosive decompression.
30:31Everything on the airplane that wasn't fastened down, tied down or secured became airborne.
30:38The noise was incredible.
30:42The 747's cargo door had torn off, ripping away a section of the fuselage.
30:48The pressurized oxygen in the cabin shot out with explosive force.
30:54And as I looked up, that was the first time I saw this tremendous hole on the side of the aircraft
30:59that was just a void, and the seats were missing,
31:03and I immediately knew that we had lost passengers.
31:07Everything in front of us was gone.
31:09Where we were sitting, we were about six inches from the hole,
31:12so there was nothing in front of us or to the side of us.
31:15The whole side of the plane was gone.
31:17Actually, our feet were dangling on the hole, and I first thought we weren't going to make it.
31:22You know, I just didn't think there was any hope.
31:25The situation is desperate, but by itself, an explosive decompression won't bring a plane down.
31:32In 811, there's a hole as big as Tulsa on the side of this thing.
31:35I mean, it's an aerodynamic disruption of massive proportions,
31:38but if it was designed the way we had designed things a long time ago, it would have unzipped.
31:44After the door came off, eventually a row of rivets held,
31:48keeping the plane from pulling itself apart.
31:54But the gaping hole is putting massive stress on the aircraft.
31:57The flight crew needs to descend as fast as possible.
32:02Left, right, valves on. Start dumping the fuel.
32:05I am dumping.
32:07Struggling to fly their badly damaged jet, the crew turn back to Honolulu Airport.
32:13And all of a sudden, we were slowing down, slowing down,
32:17and I said, oh my God, we've landed. We're on ground.
32:23Probably the best landing I've ever made.
32:26When we finally stopped on the runway, we deployed all 10 chutes,
32:32and the flight attendants evacuated all the passengers.
32:36Thanks to the experienced flight crew, United Airlines 811 landed with everyone on board alive.
32:45But nine passengers were missing.
32:47Sucked out of the plane when the fuselage tore open, taking with it five rows of seats.
32:54One of those passengers was a New Zealander on his way home, Lee Campbell.
32:59We got a phone call from Chicago, and they just said that they regret to inform us that our son was missing, presumed dead.
33:08In the wake of their son's tragic death, Kevin and Susan Campbell embark on an international mission
33:14to discover exactly why the door had come off the plane.
33:19Lee can't have died for nothing.
33:21He's a man of his word.
33:23Two months after the accident, the National Transportation Safety Board holds preliminary hearings.
33:29During a break, the Campbells take matters into their own hands.
33:33They remove several boxes full of files.
33:37So we quickly realized we'd got a real problem.
33:40We'd got a real problem.
33:42We'd got a real problem.
33:44We'd got a real problem.
33:46We'd got a real problem.
33:48We'd got a real problem.
33:50So we quickly realized we'd got a really good set of papers with a lot of things that hadn't been released to the public.
33:58We were able to really start our investigation in earnest at that stage.
34:04The unpublished documents reveal a disturbing catalogue of problems with the 747's forward cargo door,
34:10going right back to its original design.
34:14Passenger doors are plug doors, but most cargo doors on jets open outward.
34:20This increases the space for luggage and other cargo.
34:27As the plane gains altitude, the pressure inside the jet presses outward against the door.
34:33To prevent the door from opening, Boeing had installed what it believed was a foolproof locking system.
34:40What they do is they build in multiple redundancies to make sure the door is properly latched and does not open.
34:47And you build it in to a point that it's extremely improbable that the door would ever open.
34:56The Campbells' research uncovers two major flaws with the 747 cargo doors.
35:01The first involved the locking system.
35:05To lock the cargo doors, electric motors turn C-shaped latches around pins in the door frame.
35:12A handle then moves arms or locking sectors over the top of the C-latches to prevent them from reopening.
35:21But on flight 811, the supposedly foolproof system had failed.
35:28Kevin Campbell built a model of the 747 cargo door latch.
35:32It showed the first deadly flaw in the locking system.
35:36Aluminium locking sectors could not hold the C-latch in place if the latches started to open on their own.
35:47With the aluminium locking sectors, if the C-locks tried to backwind, open electrically,
35:54it would just push the locking sector out of the way.
35:59It just simply wasn't up to the job that it was designed for.
36:04But what would cause the C-lock to backwind?
36:07The Campbells didn't have the answer, but they knew they were on to something.
36:14During their research, they learned that two years before flight 811,
36:18a Pan Am 747 out of Heathrow had pressurisation problems as it climbed to cruising altitude.
36:25The pilot was forced to turn back.
36:28When they got back to Heathrow, they found that the door was hanging open an inch and a half at the bottom,
36:32and all of the locks were open.
36:36When it got to the maintenance base, they found that all of the locking sectors were either bent or broken.
36:43The passengers on this flight were lucky. They had survived the faulty locking system.
36:48But why had the C-latches turned and bent the locking sectors?
36:58As the Campbells continue to search, a Pan Am report surfaces that lays out a critical issue with the cargo door's electrical system.
37:07When the cargo door's outer handle is placed in the closed position,
37:11a master lock switch should disconnect the power supply.
37:15This would stop the C-latches from turning.
37:19But something was wrong with the switch.
37:23There was power to the door locks with the outer handle closed,
37:29and the lock started to move, and it started to force the locking sectors out of the way.
37:35The faulty power switch and weak locking sectors were no match for the pressurised oxygen inside the plane.
37:42After years of being pushed by the Campbells, the NTSB produces a report that agrees.
37:51There was an inadvertent failure of either the switch or the wiring that caused an uncommanded opening of the door.
38:01It's nice that other people know that you're right, and have been all along,
38:05It's nice that other people know that you're right, and have been all along,
38:09and the support that they had given you was vindicated.
38:14I couldn't have lived with myself if we had done no investigating ourselves.
38:19It was just something we both felt we needed to do.
38:22We didn't even discuss it, we just knew that's what we would do.
38:28After United Flight 811, the locking system on the Boeing 747 cargo doors was changed.
38:35Inspections were increased.
38:38Another potential cause of explosive decompression had been found and eliminated.
38:43That is an amazing accolade to what we've learned, not just Boeing,
38:47but what we've learned about maintenance, about structures, maintaining them and inspecting them.
38:51Since the first jet engines pushed planes higher in the sky,
38:55the aviation industry has struggled to harness and contain the deadly power of pressurized oxygen.
39:01They know all too well that a single flaw can lead to a terrifying decompression.
39:14But more than 15 years after United 811,
39:17another deadly lesson is learned.
39:21It's August the 14th, 2005.
39:26For almost an hour, Helios Flight 522 has been circling the skies over Athens.
39:33Its flight crew has stopped communicating with air traffic control.
39:38Fearing a terrorist attack, the Greek Air Force scrambles to find out what's going on.
39:44Fearing a terrorist attack, the Greek Air Force scrambles two fighter jets to circle the mystery aircraft.
40:04The fighter pilots can't see any damage to the jet. No holes in the fuselage.
40:13There's no problem, obvious problem, from the external view with the plane.
40:19Someone in the cockpit waves at the fighter pilot,
40:22but all too soon the jet loses altitude and falls towards the ground.
40:32All 121 people on board are killed.
40:36It's the worst air crash in the history of Greece.
40:44Within minutes, investigators are on the scene.
40:47So we climbed over the hill and there we were, you know, facing this situation,
40:52which was beyond any description.
40:56I saw a great area in front of me which was burning. It was black.
41:01Burning, people spread, pieces of the airplane.
41:07The autopsies add more mystery to the case.
41:11Everyone on board is dead.
41:13They did not die from inhaling a toxic substance in the airplane, or from an explosion.
41:20These people died on impact.
41:23But if the passengers were alive until impact,
41:26why didn't the fighter pilots see more activity on the plane?
41:30Akrivos Tsolakis is the lead investigator.
41:33He begins to dig through maintenance records.
41:36He learns that on the day of the crash, the rear door had been inspected for leaks.
41:42Before it took off on its last flight,
41:44the Helios jet arrived in Cyprus with a problem.
41:48It had a leak in the engine compartment,
41:50and it had a leak in the engine compartment,
41:52and it had a leak in the engine compartment,
41:54and it had a leak in the engine compartment,
41:56and it had a leak in the engine compartment,
41:58the Helios jet arrived in Cyprus with a problem.
42:01During the trip, the cabin crew had heard loud banging,
42:04and saw ice on a rear service door.
42:13To make sure there's nothing wrong with the seal on the door,
42:16the engineer runs a pressurization test.
42:19He's looking for a leak.
42:23So explain again how you tested the pressure.
42:26When I went into the cockpit,
42:28I turned the pressurization switch to manual.
42:31Switching digital pressure control unit from auto to manual.
42:36The jet's engines are turned off,
42:38so the engineer uses the plane's auxiliary power unit
42:41to force air into the cabin.
42:44It's like looking for a leak in a tire.
42:46In this case, what you're having to do is pressurize the aircraft,
42:50use a barometer essentially to monitor the pressure inside,
42:54and look for leaks that way.
42:56A normally well-maintained jetliner of any age
42:59is simply not going to be completely airtight.
43:04You're going to have leaks.
43:05As a matter of fact, as pilots,
43:06we know that certain airplanes are going to leak more than others,
43:09and you've really got to crank the pressurization up.
43:12After completing the pressurization test,
43:14the ground engineer reports that the jet is in good working order.
43:19But the digital pressure control is left in the manual position.
43:26They were supposed to return the selector to the auto position.
43:33If the flight crew fails to see that the switch is on manual,
43:37their plane won't properly pressurize.
43:40The oxygen available inside the plane
43:42will be just as thin as the outside atmosphere.
43:45The passengers will be directly exposed to a deadly environment
43:49in which they cannot survive.
43:58August 14, 2005.
44:01The worst airline disaster in Greek history has stunned the nation.
44:06Investigators are sifting through the gruesome wreckage.
44:10A few minutes after nine in the morning,
44:12Helios Flight 522 left from Cyprus bound for Athens.
44:17The crew has no idea that hours before take-off,
44:20during a maintenance test,
44:22a flight engineer has left a pressurization switch set to manual.
44:27Both the captain and co-pilot miss the fact
44:30that the plane is not set to pressurize automatically.
44:34As Helios 522 climbs, an alarm blares in the cockpit.
44:40What is it?
44:42A take-off config warning?
44:44It's a non-pressurization warning.
44:46But it sounds identical to another alarm.
44:49The pilots confuse the two.
44:52It's a critical mistake.
44:54The plane is not set to pressurize automatically.
44:58The plane is not set to pressurize automatically.
45:01It's a critical mistake.
45:03The alarm sounded and that alarm was misinterpreted.
45:08Most of the flight crew,
45:10they will never face an alarm with no pressurization
45:16in all their flight career because it's a rare event.
45:20Operations, this is Flight 522, over.
45:24Flight 522, what can I do for you?
45:26We have a take-off config warning on.
45:29Sorry, can you repeat?
45:31As the pilots troubleshoot with ground engineers,
45:34life-sustaining oxygen is slowly seeping out of the plane.
45:38Eventually, oxygen masks drop in the cabin.
45:41They do not fall in the cockpit.
45:44The reason that we don't have
45:46automatically deploying oxygen masks in a cockpit
45:49is simply too much up there,
45:51and if you had things popping out,
45:53they're going to hit switches that they shouldn't hit.
45:56The crew don't realize they have a pressurization problem.
45:59Eventually, both the captain and the co-pilot collapse unconscious.
46:04The oxygen is too thin to breathe.
46:08We're the ones that should be trained consistently
46:11to understand that ears popping,
46:13anything that indicates pressurization,
46:15you don't even talk to each other
46:17before you grab that mask and put it on.
46:20The passengers are unaware that the plane is now flying itself.
46:27In emergency situations,
46:29chemical generators above the seats pump out oxygen.
46:32But there's a catch.
46:34These generators only produce enough oxygen for about 12 minutes.
46:38The problem with the passenger masks is,
46:41for one thing, they're not designed
46:43to keep you oxygenated at a high altitude.
46:46What they're designed to do is give you enough oxygen
46:49so that you can survive
46:51until the pilots get the airplane down to a low altitude.
46:55But with both pilots already unconscious,
46:58the Helios jet did not descend
47:00so passengers could breathe without assistance.
47:05Instead, the plane flew on autopilot to Athens.
47:08When the oxygen supply stopped, the passengers passed out.
47:14By the time the Greek Air Force intercepted the Helios jet,
47:18only one person was still moving.
47:22Likely surviving with bottled oxygen,
47:24Flight Attendant Andreas Prodromou
47:26was still conscious when the fighters approached.
47:29He made it to the cockpit, but he couldn't save the plane.
47:34At the neck of the plane,
47:36the pilot is still unconscious.
47:38He can't breathe.
47:40He can't save the plane.
47:49Eventually, when its fuel ran out,
47:51Helios 522 crashed.
47:59Investigators eventually find the panel
48:01with the pressurization switch.
48:11All 121 people on the Helios flight died
48:15because their plane didn't carry enough life-sustaining oxygen
48:19as it climbed into the sky.
48:26It's been more than 50 years
48:28since the beginning of the passenger jet era.
48:3150 years in which the industry has learned,
48:34sometimes painfully,
48:37how to safely fly more than 10 kilometers in the sky.
48:41When you look back at all the other accidents
48:43over the last 20 years,
48:45in most cases, we were pushing the frontier of knowledge.
48:48Unfortunately, when you're pushing the envelope,
48:50you're pushing the boundaries of design,
48:52you can encounter problems that you hadn't anticipated.
48:58In search of the safest plane imaginable,
49:00the history of aviation traces a flight path
49:03through tragic accidents to technological breakthroughs.
49:06Many of these accidents display
49:08the incredible power of explosive decompression.
49:14The Airbus A320 and every other passenger plane built today
49:17is infinitely safer than the first jets that flew in the 1950s.
49:26They have to remain safe and get even safer
49:30because we rely so heavily on this incredible mode of transportation
49:34that takes us somewhere we were never meant to be.
50:00NASA Jet Propulsion Laboratory, California Institute of Technology