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00:00Damn it!
00:02When a passenger jet owned by Formula One superstar Nicky Lauda plummets to Earth,
00:09he's driven to find out why.
00:12Where was the tail found?
00:14I was upset that the airplane did something where a human being couldn't react anymore.
00:20When two DC-10s are brought down within two years...
00:23What happened?
00:25The cabin blew out!
00:26...investigators unlock shocking discoveries.
00:31Design flaw issues can typically affect the entire fleet.
00:36Are there other ones that are about to happen?
00:39Get out of it, champ! Come on!
00:42And a doomed commuter flight in Georgia comes down to a faulty design.
00:47My God.
00:49Our three horrific accidents, all because of deadly defects.
00:53Play design flaw that leads to a loss of an aircraft.
00:58It draws the attention of the entire world.
01:02D-D-D-D.
01:06Oh, fuck!
01:093-1-0-3-8-0-3-0-3-0-3-0-3-0-3-0-3-0-3-0-3-0-3-0-3.
01:14You need a little bit of auto trim to the left, huh?
01:33What's that?
01:34You need a little bit of auto trim to the left.
01:36Ascending to cruising altitude...
01:39Okay.
01:39...Captain Thomas Welch and First Officer Josef Therner...
01:43...are flying a Boeing 767 from Bangkok, Thailand...
01:47...to Vienna, Austria.
01:51The flight is operated by Lauda Air.
01:56The brainchild of famed Austrian Formula One driver...
02:00...and Nicky Lauda.
02:01For me, it was a logical step after retiring from racing...
02:06...to start in this kind of business.
02:08And that's what I did with Lauda Air.
02:12His new airline is a small fleet of just four planes.
02:17One of the main reasons was to give the passengers...
02:20...a different way of flying.
02:22Better service, better food.
02:24The airplane had to look in a certain way.
02:28Lauda Air Flight 4 is less than 15 minutes...
02:31...into its 11-hour flight to Vienna.
02:35Capture 13.
02:37I'm going to pass it in.
02:39In the cockpit, Captain Welch and First Officer Therner...
02:46...monitor their instruments...
02:47...while the autopilot controls the climb.
02:57Suddenly, the plane begins dropping from the sky.
03:05Wait a minute!
03:07In an instant, the pilots lose all control.
03:17And their jet plunges towards the ground.
03:20In a matter of seconds, the jet falls more than 20,000 feet.
03:41The plane slams into a remote jungle...
03:44...110 miles northwest of Bangkok.
03:47I was at home and I had a phone call from the news.
03:52They said one of our airplanes crashed.
03:56When rescuers arrive, it's immediately obvious...
03:59...that there's no one to be rescued.
04:02All 213 passengers and 10 crew members are dead.
04:07It's the first time a Boeing 767 has ever crashed.
04:18The loss of a U.S.-made aircraft...
04:20...prompts quick action from the National Transportation Safety Board, or NTSB.
04:26Bob McIntosh is assigned to the investigation.
04:28A first crash of an aircraft that was in service intercontinentally...
04:36...for almost a decade with a perfect service record.
04:40It was extremely important for us to learn what had happened.
04:45He finds the badly burned wreckage strewn over a square mile of rough terrain.
04:54The major components, the cockpit, the tail, the main body...
04:59...they were scattered far enough apart...
05:01...that certainly they had not come down together.
05:06McIntosh immediately knows the plane broke up during the flight.
05:09What he needs to uncover is why.
05:23Where was the tail found?
05:25Airline owner Nicky Lauda arrives in Thailand to help find the answer.
05:31The scene for me, this was the most horrific pictures I've ever seen.
05:36Surrounded by the scattered remains of an airliner that carries his name...
05:43...Lauda is overwhelmed by the magnitude of the disaster.
05:47When you have 223 people killed, the families all want to know why.
05:55And I think this is the worst for people if they do not know why...
05:58...they lost their husband, children, or whatsoever.
06:00The black boxes may have captured important clues about the cause of the in-flight break-up...
06:07...but they're badly burned.
06:12They're sent to NTSB technicians in Washington.
06:15Then, days after the crash...
06:24Well, would you look at that.
06:28...more pieces of the plane are found, including one of the engines.
06:35And investigators are amazed by what they see.
06:38The thrust reverser on Flight 4's left engine is fully deployed.
06:47Once we actually saw that the thrust reverser had deployed...
06:52...for me, it was shocking.
06:55Thrust reversers are only used on landing.
06:59Once activated, they direct airflow forward...
07:02...helping the 767 come to a stop.
07:05They should never be deployed in the air.
07:10And even if it does happen...
07:12...a deployed reverser shouldn't cause a crash.
07:18This discovery is the biggest break so far...
07:21...and investigators need to know...
07:24...was a deployed thrust reverser responsible for the crash?
07:27But the team will have to solve the mystery...
07:37...without their most valuable tool.
07:40The flight data recorder is so badly burned...
07:43...the technicians at the NTSB can't recover any data.
07:49Thankfully, the cockpit voice recorder has survived.
07:53Ready to go.
07:54Investigators and Nicky Lauda...
07:58...listen to the last moments of Lauda Air Flight 4.
08:0280 knots.
08:03Check.
08:05Five and a half minutes into the 15-minute-long flight...
08:08...everything is normal.
08:11Then, the first sign of trouble.
08:14Chaser?
08:16That keeps...
08:18It's come on.
08:20What's come on?
08:20Some kind of warning.
08:24They discover Lauda pilots discuss a mysterious cockpit warning...
08:29...moments before the crash.
08:31It's a warning that relates to a hydraulic valve...
08:35...in the left engine's thrust reverser.
08:37The hydraulic isolation valve...
08:40...controls the flow of hydraulic fluid to the reversers.
08:44Opening the valve allows the reverser to be stowed or deployed.
08:48When it's closed, the reversers won't budge.
08:51Okay.
08:54The crew doesn't sound worried about the warning.
08:58It's probably moisture or something.
09:04For five minutes, nothing happens.
09:08Then...
09:08Just 22 seconds later...
09:20...there's the sound of the plane ripping to pieces.
09:28The whole thing was so difficult.
09:32You never forget.
09:33More motivated than ever...
09:39Lauda sets out to prove a controversial theory...
09:42...explaining why his plane went down.
09:44I was after Boeing day and night...
09:48...so that the people understand that we're working on it.
09:52That we hopefully find the cause...
09:54...and make sure we'll never ever happen again...
09:56...because this is the answers...
09:57...these families needed.
09:58Nicky Lauda travels to Boeing headquarters in Seattle...
10:05...to investigate the 767's thrust reversers.
10:09It's my name, my airplane, my crash...
10:13...and Boeing understood my problem or their problem...
10:16...and we kept on working together.
10:19Before the 767 first went into service...
10:22...Boeing ran certification tests...
10:24...to prove that pilots could keep flying safely...
10:27...in the event of a mid-air reverser deployment.
10:35The tests proved that the 767...
10:38...was capable of continued safe flight and landing...
10:41...regardless of the position of the thrust reverser.
10:44The widespread feeling of what would happen...
10:52...if a reverser deployed in flight...
10:55...was that the airplane would be controllable.
10:59But despite Boeing's certification tests...
11:03...Lauder believes the reverser is to blame.
11:06I know what it says, but that's not what happened in Thailand.
11:09And he's determined to figure out why a failure...
11:13...that's not supposed to be dangerous...
11:15...killed 223 people flying on his airline.
11:20Okay, let's try it in a simulator.
11:23Nicky Lauda works with Boeing investigators...
11:26...to recreate the flight.
11:28Okay, let's begin.
11:31He sets the flight's altitude to 24,000 feet...
11:35...more than double the 10,000 feet...
11:37...that Boeing used for their thrust reverser certification.
11:41Could the altitude difference explain what happened?
11:46It was incredible...
11:48...because the airplane just turned around...
11:50...and you couldn't do anything.
11:54Lauda now knows definitively...
11:56...why his plane dropped so unexpectedly.
12:01When the thrust reverser deployed...
12:04...the smooth flow of air over the wing was disrupted...
12:07...dramatically decreasing lift.
12:12Reverse is deployed!
12:13This forced the jet into a sudden, terrifying nosedive.
12:18It was just too late.
12:19The aircraft was going to assume...
12:20...a very nose-low, high-speed attitude.
12:25Incredibly, Nicky Lauda has proven...
12:28...Boeing's certification test was lacking.
12:30He's shown that above 20,000 feet...
12:34...where planes fly faster...
12:36...the accidental deployment of a thrust reverser...
12:39...can be fatal.
12:40It was evident to the Boeing company...
12:44...and to the FAA certification authorities...
12:48...and to the operators of Boeing 6, 767s around the world...
12:52...that this was going to be a major, major issue.
12:56The reverser deployed...
12:57...and those guys couldn't recover.
13:03Let's figure out why that happened.
13:05Now, the 767's thrust reversers...
13:12...undergo intensive study at Boeing.
13:16Engineers can imagine only one scenario...
13:19...that might make a reverser deploy...
13:20...unexpectedly in mid-air.
13:23The theory calls for the activation...
13:26...of the two valves...
13:27...in the reverser's fail-safe system...
13:29...at the same time.
13:30The first valve is the isolation valve...
13:34...that controls the flow of hydraulic fluid.
13:37When the second valve...
13:38...called the directional control valve...
13:40...is activated...
13:41...fluid freely moves the reverser...
13:43...from stowed to deployed.
13:46You have to have both the isolation valve open...
13:50...and the directional control valve...
13:52...at the engine...
13:53...open to the deployed position.
14:00After extensive testing...
14:09...engineers finally make a major breakthrough.
14:13They're able to trigger...
14:15...the double failure needed...
14:16...to accidentally deploy a reverser.
14:21We could get that system to activate...
14:24...by introducing a short...
14:27...in a direct short in a system.
14:30Investigators consult with Boeing engineers...
14:33...on the 767's infrastructure.
14:36They discover that the wires for both valves...
14:40...were bundled in the same harness.
14:42A fault across several wires...
14:44...in the same harness...
14:45...could have triggered...
14:46...simultaneous short circuits.
14:50Two shorts...
14:52...in two valves...
14:54...at exactly the same time?
14:57What are the odds?
14:58I was upset...
15:01...that the airplane did something...
15:04...where a human being couldn't react anymore.
15:08Investigators have revealed...
15:09...a serious design flaw...
15:11...that allows thrust reversers...
15:13...to deploy accidentally.
15:18Pressure builds for a full review...
15:20...of the thrust reverser system...
15:22...on all 767's.
15:23There were other airlines...
15:26...that joined in the questioning...
15:28...of how could this...
15:29...possibly affect the flight path...
15:31...to the point where you lose control.
15:35As a result of the Lauda investigation...
15:38...a series of mechanical locks...
15:41...now ensure that...
15:42...even if both valves...
15:43...get energized in flight...
15:45...the reversers can't deploy.
15:51For Nicky Lauda...
15:52...the outcome of this investigation...
15:54...is total vindication.
15:56For me the worst thing in life...
15:58...is grey areas.
15:59I hate grey areas...
16:01...and there are a lot of airplane crashes...
16:03...been in the past...
16:04...where you really do not know...
16:05...exactly what happened.
16:08And in this crash here...
16:09...thank God...
16:10...it was clear what was the cause...
16:15...and it was fixed...
16:16...for all airplanes worldwide.
16:21Even when new airliners...
16:22...go through exhaustive testing...
16:24...before they're put in service...
16:26...a design flaw can occasionally...
16:28...slip through the cracks.
16:29I think due to the complexity...
16:32...of these aircraft...
16:33...there are any number of things...
16:36...can go wrong...
16:37...even under the best set...
16:38...of circumstances.
16:43Seventeen years earlier...
16:45...is a deadly design flaw...
16:47The captain flew out!
16:48...responsible...
16:50...for the worst air crash...
16:51...to date.
17:01Turkish Airlines Flight 981...
17:03...is boarding at Orly Airport...
17:04...in Paris.
17:08Normally the last leg of this trip...
17:10...from Turkey to England...
17:11...isn't very crowded.
17:14But today...
17:15...the DC-10 is filling up fast.
17:17With all the new...
17:21...passengers boarding...
17:22...Captain Nejad Berkhoz...
17:24...and co-pilot Oral Ulusman...
17:26...are running a little...
17:27...behind schedule.
17:32So is baggage handler...
17:33...Mohamed Mahmoudi...
17:35...who's loading the luggage...
17:37...of all 335 passengers.
17:39Not expecting any more bags...
17:48...Mohamed Mahmoudi...
17:49...locks the rear cargo door.
17:59The DC-10 is set to go.
18:01Just after 12.30...
18:10...in the afternoon...
18:11...Flight 981...
18:12...lifts off...
18:13...into the skies above Paris.
18:19Tango Hotel Yankee 981...
18:20...you have cleared...
18:21...the flight level 230.
18:23981, roger.
18:26As it flies away...
18:27...from the airport...
18:28...the DC-10 continues...
18:30...to gain altitude.
18:38They're still climbing...
18:39...at 10,000 feet...
18:42...when disaster strikes.
18:51The huge jet shudders...
18:53...and begins to drop.
19:01What happened?
19:03The cabin flew out!
19:06As the nose pitches down...
19:08...the plane picks up speed...
19:10...and the crew struggles...
19:11...to save their plummeting jet.
19:13Bring it up!
19:15Put our nose up!
19:17I can't bring it up!
19:18She doesn't reach far!
19:19No!
19:22In the cabin...
19:23...two rows of seats...
19:24...have simply disappeared.
19:28Anything not bolted down...
19:30...flies out of the plane...
19:31...through a gaping hole...
19:32...in the cabin floor.
19:33It looks like we're...
19:34...going to hit the ground!
19:35Me!
19:36It looks like we're...
19:37...going to hit the ground!
19:38Me!
19:39Out!
19:40Me!
19:58Turkish Airways Flight 981...
20:00...disintegrates at impact.
20:02None of the 346 people...
20:06...on board survive.
20:09It becomes the worst...
20:10...plane crash to date.
20:17Paul Eddy is a journalist...
20:18...who covered the story...
20:19...as it unfolded.
20:24It was just a scene...
20:25...of absolute utter devastation.
20:28I still have nightmares about this.
20:32Investigators for the...
20:33...French Accident Investigation Bureau...
20:35...are on the scene.
20:37My first job...
20:39...was to...
20:41...evaluate...
20:42...the scope...
20:43...of the wreckage...
20:45...and...
20:46...begin the first...
20:47...invigation on the spot.
20:51Despite the enormous force...
20:53...of the crash...
20:54...the black boxes survive.
20:57Their contents...
20:58...could provide...
20:59...valuable clues.
21:06The inquiry...
21:07...takes a bizarre turn...
21:08...when investigators...
21:09...are called to a field...
21:10...nine miles...
21:11...from the main crash site.
21:16They find the rear cargo door...
21:19...and two rows of seats...
21:20...that somehow fell...
21:21...from the DC-10.
21:23Since the accident...
21:26...involves an American plane...
21:28...Chuck Miller...
21:29...from the National Transportation...
21:30...Safety Board...
21:31...joins the investigation.
21:33He was a very, very...
21:36...professional man.
21:38Chuck didn't sit back...
21:39...in the office.
21:40Chuck was always...
21:41...on the scene.
21:45For him...
21:46...the scene is eerily familiar.
21:49For the second time...
21:50...in two years...
21:51...he's dealing...
21:52...with a DC-10.
21:53In June 1972...
22:00...a plane's cargo door...
22:03...and some cargo...
22:04...were found in a field...
22:05...18 miles...
22:06...from Windsor, Ontario...
22:07...Canada.
22:10They had been ripped...
22:11...from a brand new DC-10...
22:12...as it flew to Buffalo.
22:20But the Windsor incident...
22:21...ended differently...
22:22...as the pilots...
22:23...of American Airlines...
22:24...Flight 96...
22:25...were able to land...
22:26...the plane safely.
22:29When the flight crew...
22:30...finally saw the damage...
22:31...they were stunned...
22:32...by a hole...
22:33...where the cargo door...
22:34...would normally be.
22:36The captain and I...
22:37...walked back to the...
22:38...back...
22:39...and...
22:40...we just looked up...
22:41...and saw this hole.
22:43And it was just...
22:44...so weird.
22:49It didn't take investigators long...
22:50...to realize...
22:51...the very design...
22:52...of the cargo door...
22:53...carried a latent...
22:54...fatal flaw.
22:57When it closes...
22:58...hooks on the DC-10's...
23:00...cargo door...
23:01...grab hold of a bar...
23:02...on the plane's...
23:03...door frame.
23:04To make sure...
23:05...it's locked...
23:06...baggage handlers...
23:07...push down on the lever...
23:08...which drives...
23:09...locking pins...
23:10...through the hooks...
23:11...that hold them in place.
23:14Without this...
23:15...heavy duty mechanism...
23:16...the extreme air pressure...
23:18...thousands of feet in the air...
23:19...would rip the door...
23:20...right off the plane.
23:25The 1972 discovery...
23:27...was terrifying.
23:30The NTSB...
23:31...realized...
23:32...it was possible...
23:33...to close the lever...
23:34...on the outside of the door...
23:35...even if the hooks...
23:37...and locking pins...
23:38...were not in the closed position.
23:39Engage the lever.
23:41That meant...
23:43...baggage handlers...
23:44...could believe...
23:45...the door was locked...
23:46...when it wasn't.
23:52In the Windsor incident...
23:54...there was...
23:55...an obvious flaw...
23:56...and that's where...
23:58...the NTSB...
23:59...said...
24:00...let's make sure...
24:01...we change this system...
24:02...right now...
24:03...every DC-10 operator...
24:04...needs to know this.
24:05In 1972...
24:08...Chuck Miller's reports...
24:10...strongly recommended changes...
24:12...to the DC-10's...
24:13...cargo door locking mechanism...
24:15...be made as soon as possible.
24:22Two years later...
24:24...as Miller inspects...
24:25...the Turkish Airlines crash site...
24:27...he's immediately troubled.
24:31If Miller's recommendations...
24:32...were implemented...
24:33...after the Windsor incident...
24:35...why has another...
24:36...DC-10 cargo door...
24:38...been ripped from its plane?
24:40When he saw the door...
24:42...saw that the fix...
24:43...hadn't been made...
24:44...that's when...
24:45...I think his anger...
24:47...became very, very strong indeed.
24:52Miller takes an unusual step.
24:55Although the official investigation...
24:57...is just beginning...
24:58...he gives journalist Paul Eddy...
25:00...an important tip.
25:01I said, have you got any ideas...
25:03...what made the door come off?
25:04And he said, yeah.
25:06If I were you...
25:07...I'd go and look at a place...
25:08...called Windsor, Ontario.
25:16Suspecting that...
25:17...two similar incidents...
25:18...within two years...
25:19...with the DC-10 are connected...
25:21...I'm Chuck Miller.
25:23NTSB investigator Chuck Miller...
25:25...shares his theory...
25:26...with French investigators.
25:30These were taken...
25:31...on June 12th...
25:33...1972...
25:35...right after the incident.
25:36We asked for the report...
25:41...on the Windsor accident...
25:43...and our...
25:45...American colleagues...
25:47...were also...
25:48...volunteers...
25:49...to give us...
25:50...a lot of details.
25:53The French team are astonished...
25:55...by what Miller shows them.
25:57Now we had an American Airlines...
25:59...flight from Detroit...
26:01...to Buffalo...
26:02...have its cargo door blow off.
26:04And he has been very frank...
26:10...and has explained...
26:11...what he was thinking...
26:12...of the Windsor accident.
26:17With the information...
26:18...from Chuck Miller...
26:19...French investigators...
26:20...take a closer look...
26:21...at the plane's cargo door.
26:25There is no new problem.
26:27It's just like...
26:28...the 1972 American Airlines case...
26:31...all over again.
26:34The latches...
26:35...that are supposed to hold...
26:36...the cargo door closed...
26:37...aren't locked.
26:41What you've got to...
26:42...now discover...
26:43...is...
26:44...why wasn't that door fixed?
26:46So...
26:47...I don't think it's...
26:49In the wake of the 1972...
26:51...Windsor incident...
26:52...the NTSB...
26:53...had made very specific...
26:55...recommendations...
26:56...to the Federal Aviation Administration.
26:58Engage the lever.
27:01Most importantly...
27:02...they suggested...
27:03...that a change...
27:04...be made...
27:05...to the locking mechanism.
27:12But in the two years...
27:13...since that accident...
27:16...none of those recommendations...
27:18...had been implemented...
27:19...by McDonnell Douglas...
27:20...the company...
27:21...who manufactures...
27:22...the DC-10.
27:26In fact...
27:27...the FAA...
27:28...never issued...
27:29...an airworthiness directive...
27:31...a legal requirement...
27:32...that would ensure...
27:33...fixes were made.
27:35It's the job of the NTSB...
27:37...to...
27:38...discover...
27:39...what's happened...
27:40...uh...
27:41...and...
27:42...to come up with...
27:43...recommendations...
27:44...as to how to prevent...
27:45...it happening again...
27:46...but it has absolutely...
27:47...no authority...
27:48...to implement them.
27:51Investigators learned...
27:52...that McDonnell Douglas...
27:53...had made some minor changes...
27:55...to the cargo doors.
27:59A peephole...
28:00...was cut in the bottom of the door...
28:01...so baggage handlers...
28:02...could see...
28:03...if the locking pins...
28:04...had engaged.
28:06Several warning signs...
28:07...were also attached...
28:08...to the plane's door.
28:11But sadly...
28:12...those fixes...
28:13...just created...
28:14...their own problems.
28:16Many baggage handlers...
28:17...didn't know...
28:18...what the small hole...
28:19...in the door was for.
28:24The baggage handler in Paris...
28:25...read and spoke...
28:26...three languages...
28:28...but not English...
28:29...the only language...
28:30...in which the warning signs...
28:31...were written.
28:33But in the eyes of Chuck Miller...
28:36...these were band-aid solutions.
28:39The fundamental flawed design...
28:41...with the locks...
28:42...remained the same...
28:43...allowing history...
28:44...to repeat itself...
28:45...just two years later.
28:46There is no question...
28:48...that if an airworthiness directive...
28:50...had been issued...
28:52...as it should have been...
28:53...after winter...
28:54...Paris would not have happened.
28:56It was an entirely...
28:57...avoidable accident.
28:58After the Paris crash...
28:59...fool-proof changes...
29:00...were finally made...
29:01...to the DC-10's cargo door.
29:02Well in aviation...
29:03...it's called tombstone technology.
29:04In other words...
29:05...we always have the balance of money.
29:06And unfortunately...
29:07...we have had to wait...
29:08...until we had enough people...
29:09...die in an accident...
29:10...to say...
29:11...you know...
29:12...we really are going to have...
29:13...to spend the money over here.
29:14Atlantic Southeast Airlines...
29:15...flight 23-11 cruises...
29:16...at 15,000 feet.
29:17This is Captain Friedland...
29:18...on the flat deck.
29:19We've got a bit of weather...
29:20...ahead of us...
29:21...but we're going to go around...
29:22...and give you...
29:23...a pretty smooth ride.
29:24At the controls...
29:25...of the Embraer...
29:26...the Embraer...
29:27...the Embraer...
29:28...the Embraer...
29:29...the Embraer...
29:30...of the Embraer...
29:31...of the Embraer...
29:32...and people die in an accident...
29:33...to say...
29:34...you know...
29:35...we really are going to have...
29:36...to spend the money over here.
29:37Atlantic Southeast Airlines...
29:38...flight 23-11 cruises...
29:39...at 15,000 feet.
29:40This is Captain Friedland...
29:41...on the flat deck.
29:42We've got a bit of weather...
29:43...ahead of us...
29:44...but we're going to go around...
29:45...at the controls...
29:48...of the Embraer 120...
29:50...is Captain Mark Friedland.
29:52He's an experienced pilot...
29:54...with almost 12,000 flight hours.
29:58First Officer Hank Johnston...
30:00...has been flying...
30:01...with Atlantic Southeast Airlines...
30:02...for nearly three years.
30:07This was a normal day...
30:08...in the life of the crew.
30:10Nothing untoward had happened...
30:11...and I doubt...
30:12...they were expecting...
30:13...any difficulties with the flight.
30:14Let's go...
30:16...20 degrees to the right.
30:22Today's flight...
30:23...is a short commuter route...
30:24...from Atlanta, Georgia...
30:25...to the city of Brunswick...
30:27...on the Atlantic coast.
30:30There are 20 passengers...
30:32...on today's flight.
30:37The runway's inside.
30:39The crew is just five minutes...
30:41...from touching down.
30:43ASA 2311.
30:44ASA 2311.
30:46Clear direct to Jet 1.
30:47LINCO.
30:48Report the airport in sight.
30:50Expect a visual.
30:52We do have it in sight.
30:532311.
30:55Slow in for approach speed.
30:59The aircraft was normal.
31:00There was nothing unexpected.
31:02Then the captain notices...
31:06...an unusual sound.
31:10It's weird.
31:11Number one seems to be...
31:12...spinning faster.
31:15The left is...
31:16...the left is pulling a bit more.
31:19Bringing power down to the left.
31:20Captain Friedlein tries to compensate...
31:23...for the plane's unexplained...
31:25...pull to the left.
31:31Flight 2311 is less than a thousand feet...
31:33...from the ground.
31:34And the plane is getting...
31:35...more and more difficult to control.
31:37What's going on?
31:38Do you see anything?
31:39There's nothing.
31:40The crew were apparently caught...
31:41...completely by surprise by something.
31:42What's going on with this thing?
31:43I can't hold it.
31:44Get out of it!
31:45Come on!
31:47The plane is dropping out of the sky...
31:48...and the crew doesn't know why.
31:50As flight 2311 plummets to earth...
31:52...Captain Friedlein...
31:53Come on!
31:54No!
31:55...fights desperately to save his plane.
31:59It's no use.
32:01The plane is dropping out of the sky...
32:03...and the crew doesn't know why.
32:04The plane is dropping out of the sky...
32:07...and the crew doesn't know why.
32:09As flight 2311 plummets to earth...
32:11...Captain Friedlein...
32:12...Fights desperately to save his plane.
32:14It's no use.
32:17all 20 passengers and three crew members are killed at the moment of impact
32:30wreckage is still smoldering when ntsb investigator jim ritter arrives at the crash site
32:44okay let's start here and work backwards to first impact i want a record of everything
32:49you need to look at the crash site to collect the physical evidence
32:54that's the most important aspect of any aircraft investigation
32:59at the same time witnesses tell investigators they saw the plane roll hard to the left before it hit
33:08the ground and they come right over top of the house and it got real loud it was coming right
33:15over these trees here and then it got extra loud we knew that it was some kind of very abrupt failure
33:23that would have been difficult for the flight crew to overcome
33:27what could make it roll so far over
33:36as investigators scour the wreckage searching for clues
33:41ritter knows they'll be working without any on-board flight recorders
33:48in 1991 commuter planes aren't required to carry them without the black boxes it's basically a process
33:56of elimination we analyze all of the physical evidence and come up with the most compelling
34:01scenario that matches that evidence so far the investigators best clue is the steep left roll
34:09before impact when the airplane rolled to the left it could really only be due to two things perhaps the
34:18pilot wanted to roll to the left or there was a malfunction that the pilots couldn't counteract
34:26but when investigators study the engines they find that they were operating normally at the moment of impact
34:41ritter turns his attention to the other main part of the plane's propulsion system
34:45let's take a look at these propellers when we started doing testing the propeller system we didn't know
34:50it was an elitist but it was something we had to eliminate of nothing else
34:57deep inside the propeller unit investigators uncover an important clue
35:02there's a small mark where the base of the propeller slammed into its housing during the crash
35:18it might be enough to tell investigators how the propellers were operating at the moment of impact
35:25you can literally match up the scratch marks between both pieces
35:30and you'll know what the angle of the propeller blade was from that measurement mark this one
35:3922 degrees
35:43the Embraer 120 has what's called a constant speed propeller the blades spin at a steady rate in flight
35:52when the pilots need more power the blades twist changing their angle to take a bigger bite out of the air
35:59and provide more thrust slow in for approach speed and in flight it acts like the automatic
36:09transmission in a car it's as if it's changing gears to match the engine load
36:15the marks tell ritter the exact angle of the blades when the plane slammed into the ground
36:20we immediately noticed the difference between
36:23some of the blade angle measurements for the left engine versus the right engine
36:29the blades were almost flat
36:33at three degrees the blades are so flat they would act like a wall
36:38blocking the flow of air the plane needs to maintain lift
36:41it might have caused the pilots to lose control
36:52investigators study the mechanism used to control the left propeller
36:56will you look at this
37:00it's completely worn down
37:03the teeth on a key gear mechanism known as the quill are almost entirely worn away
37:08this is what it's supposed to look like
37:18with its teeth worn away the quill can't effectively lock onto the gear system that controls the angle of
37:25the propeller blades
37:26that really was a eureka moment for us because now we had a serious malfunction that we could examine
37:42investigators study the design of the propeller mechanism
37:46they learned that shortly before the accident the propeller manufacturer started using a harder
37:57more abrasive coating on a key part known as the transfer tube which meshes with the quill teeth
38:03they turned it into a giant file
38:08so the splines on the transfer tube were much harder and rougher than the quill teeth and it was almost like sandpaper
38:15so the tube was actually wearing down the teeth on the quill
38:24investigators now understand why the quill teeth were worn down
38:28without functional quill teeth the propeller blades could slip into a dangerously flat position
38:36to prove their new theory investigators need to take a huge risk we've got to see what happens in the air
38:43and test the damaged propeller system under full flight conditions
38:48i said well the only way to really know is let's do a flight test and find out because we're at a point
38:54in investigation we need to start eliminating things
39:02the investigation into the crash of flight 2311 moves to embraer headquarters in brazil
39:11investigator tom hauter meets with the representatives from embraer and the propeller manufacturer
39:17thank you for doing this
39:18embraer's chief test pilot gilberto scatini will fly an embraer 120 that has been modified to recreate
39:26the failure of flight 2311 so we've modified the quill the teeth have been worn down just like flight 2311
39:35a worn quill is placed inside the propeller unit
39:40this was potentially very high risk because once we disconnected the transfer tube in flight
39:46the pilots would have no way to control the propeller we put a pitch lock here
39:52it won't go past 22 degrees a mechanical lock has also been added to stop the propeller from going
39:59flatter than 22 degrees not three degrees as happened on flight 2311 it would be too dangerous in the flight
40:08test to have the propeller blade go all the way to flat pitch you'd lose control of the airplane that was
40:13almost almost guaranteed
40:22bmb 120 do you copy what if this airplane crashes what if we lose the airplane
40:29i'm the one you know who's basically running this test uh this could be all my responsibility
40:34copy we are ready to disengage the prop
40:43propeller blade angles causing no problems no control issues
41:01then the brazilian test flight takes a dramatic turn
41:05as the flight continues the blades begin drifting towards the deadly flat position
41:15reducing speed
41:18easy does it
41:24we started feeling a rolling moment to the left
41:26the blades go as flat as this test will allow
41:38for how to the risky test flight has paid off
41:43the investigators theory about the crash is back on solid ground
41:48seeing the data right then it took a load off so wow i mean we now know what happened it was obvious
41:57investigators finally understand the full story behind the crash of flight 2311
42:03when the flight crew began preparations for landing the teeth on the quill were worn down still operational
42:10slowing for approach speed preparing for landing put renewed pressure on the already worn teeth in the quill
42:18the teeth could no longer stay locked on the left propeller mechanism
42:31and once the teeth gave way the propeller blades were free to drift into a fatally flat position
42:39what's going on with this thing i can't hold it
42:41the propeller's design couldn't hold the blades at a safe angle and the plane became less and less controllable
42:52human error is almost always underneath the causes of an accident
42:57even if it wasn't the pilot or a mechanic in this particular case an engineering change was made which
43:03well-intentioned actually did not work out oh that's it oh god
43:10no
43:15the warren quill teeth was a time bomb waiting to go off
43:20after the accident additional safeguards are added to prevent this type of failure
43:25a change that affects not only umbrella but several other turboprop aircraft
43:35airline manufacturers are constantly trying to stay ahead of potentially fatal design flaws
43:42air crash investigators are determined to make sure they do
43:47what's important is getting to the truth
43:49so if the truth is something that may hurt the company let the chips fall where they may