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United Airlines Flight 232, a McDonnell Douglas DC-10 en route to Chicago from Denver, experiences a catastrophic failure of the titanium fan disk in its tail engine. The pilots try to land at Sioux City, Iowa. As the DC-10 descends it rolls right just above the ground. The DC-10 crashes and explodes into a fireball, killing 112 of the 296 people on board. 184 people survive the accident, in part thanks to a deadheading training-check and an airman named Dennis Edward Fitch who was able to provide assistance to the flight crew in controlling the DC-10.
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00:01A DC-10 en route to Chicago. It's packed with children and vacationers.
00:07One hour into the flight, an engine fails.
00:12Although it still has two good engines, the plane becomes almost unflyable.
00:20285 passengers face an horrific crash landing at Sioux City.
00:25Why did a simple engine failure lead to a crash?
00:29Now, using advanced computer simulations, we reveal exactly what downed Flight 232.
00:39Disasters don't just happen, they're a chain of critical events.
00:43Unravel the clues and count down those final seconds from disaster.
00:59Colorado. Denver. Stapleton Airport. July 19th, 1989.
01:07Known as the Gateway to the Rockies, Denver is the starting point for journeys all over the US.
01:151,300 planes take off from here every day, carrying over 75,000 passengers.
01:23It's the peak of the summer season, and Stapleton is packed with vacationers and business travelers.
01:35Debbie McKelvey will be among the vacationers flying from Stapleton today.
01:41She's taking her children, Devon, age six, and her son Ryan, who's seven, to a family reunion back in her
01:47home state of Pennsylvania.
01:51I was going home for two weeks with my children, and I was very, very excited about the trip.
01:58Debbie is taking advantage of United Airlines' Children's Day promotion.
02:03Today, kids under 14 can fly for one set, but each must fly with a paying adult.
02:11Debbie pairs up with a tennis club girlfriend, Ruth Ness, so she can sit with one of the kids.
02:17It was nice having Ruth with me, because she entertained one child while I was entertaining the other child.
02:241,15 p.m.
02:26Debbie, Ruth, and the kids wait to board flight UA232 to Philadelphia via Chicago.
02:37Commanding the flight is Captain Alfred C. Haynes.
02:41His cabin staff reported a minor electrical fault in the galley on the previous leg, but engineers have given it
02:47the all clear.
02:50Captain Haynes is a veteran pilot with 7,190 hours logged in the DC-10.
02:58The passengers will be in safe hands today.
03:01The DC-10 is a great airplane to fly.
03:04I think I was termed an old man's airplane because it's so simple to fly.
03:08At this time in the late 1980s, there are over 400 DC-10s in service.
03:15But it's a plane with a troubled history.
03:20Windsor, Ontario, 1972.
03:23A cargo door blows out on a year-old DC-10, causing severe decompression.
03:30The pilots manage to land the plane safely.
03:33Two years later, a door comes off a Turkish Airlines DC-10 flying out of Paris.
03:40This time, the violent decompression tears the plane apart in mid-air.
03:45All 346 people on board die.
03:51McDonnell Douglas finds the fault and fixes it.
03:54But the reputation of the DC-10 never fully recovers.
04:02The DC-10, making flight 232 today, is in its 17th year of service.
04:07And has flown over 43,000 hours.
04:11So far, with that incident.
04:14Today, should be no different.
04:20Jerry Schemmel is Deputy Commissioner of the Continental Basketball Association.
04:25And a frequent flyer.
04:28I was never a nervous flyer.
04:29I always kind of enjoyed flying.
04:31I took my first flight at age 18.
04:33I always enjoyed it.
04:35Jerry is flying to Columbus on business with his boss and great friend, Jay Ramsdell.
04:42Their original flight is cancelled.
04:44But Jay gets a seat on the very next flight.
04:47The bad news is, there's no seat for Jerry.
04:51Jay decides to stay with his buddy and wait for an even later plane.
04:55I didn't think much out at that time.
04:57I thought it was a nice gesture.
04:58I thought to myself, I hope I would have done the same thing.
05:05Finally, after a six and a half hour wait, Jerry and Jay both get seats on flight UA232 to Philadelphia.
05:16Flight 232 is busy today.
05:18It's carrying 285 passengers and 11 crew.
05:24Debbie McKelvey boards with her friend and two kids.
05:28They add to an unusually high number of children on board.
05:3352 in total, thanks to the Children's Day deal.
05:38For senior flight attendant, Jan Brown Law, lots of children on board means a busy flight ahead.
05:46After a four day trip, Jan is excited to be heading home to Chicago.
05:52I just remember feeling just the energy of this last leg and getting all pumped up to do the service.
06:01Captain Haynes, co-pilot Bill Records, and flight engineer Dudley Dvorak run through their pre-flight checks.
06:09They taxi out to the runway and await the takeoff clearance.
06:14At 2.09pm, the three engine jet flies out of Denver.
06:19The morning we left Denver, it was clear skies.
06:21Beautiful day, nice smooth air, comfortable flight.
06:25Just a routine flight.
06:30Debbie McKelvey sits with her son Ryan while her friend Ruth is one row behind, looking after her daughter Devon.
06:37At 3.16pm, they're finishing their meal.
06:50What the hell was that?
06:51Suddenly, out of the blue, a terrifying blast rips through the plane.
06:56The first thing I thought was a bomb has gone off.
06:59I really did. I thought someone had planted a bomb, it had been detonated, and we started to drop.
07:04The only way I can think to explain it, it's like if you're driving down a highway and you hit
07:09a pothole.
07:11Jan Brown Law fears it may be a breach in the plane's fuselage.
07:15I instinctively sat down on the floor and held on, not knowing if it were a decompression, that everything that
07:23isn't tied down securely is going to be sucked out.
07:26There's no sign of any visible damage inside the plane.
07:29But up in the cockpit, Captain Haynes scans the engine instruments and quickly realizes that his number two engine is
07:37malfunctioning.
07:38I've never had a jet engine fail in flight. Only in the flight simulator. Never in flight.
07:43But this time, it's happening for real.
07:473.17pm.
07:49Captain Haynes' priority is to shut down the problem engine.
07:53He's not too worried the DC-10 can fly comfortably on its remaining two wing-mounted engines.
07:59Haynes follows the shutdown procedure and cuts off fuel and power to the number two engine.
08:10The problem engine is off. But now flight engineer Dudley Dvorak spots something else wrong.
08:16Now we've lost our hydraulic quantity.
08:18His instruments tell him that all three of the plane's hydraulic systems are empty.
08:23He cannot believe his eyes.
08:26The hydraulic systems operate the plane's flaps, ailerons, rudder and elevator.
08:36Without these controls, the pilots won't be able to steer the plane or take it up or down.
08:43But the instruments are right.
08:46Al, can you help me out with this?
08:47Co-pilot Bill Records is horrified to find his flight controls are no longer responding.
08:52We've got the right way down.
08:54The plane starts to bank steeply to the right, and he's powerless to stop it.
08:58That's when we realized we were in a world of hurt.
09:02Something was drastically wrong.
09:06Now Captain Haynes tries the flight controls.
09:09But he cannot get the DC-10 back into level flight either.
09:14The plane is now trying to roll over a terrifying prospect.
09:21We have nothing to turn the airplane, nothing to control the pitch of the aircraft.
09:26Why the aircraft?
09:28It's every pilot's nightmare.
09:30Flight 232 is at 11,000 meters and out of control.
09:35If its left wing continues to lift, the plane will flip over and tumble to its doom.
09:45United Airlines flight 232 is down to two engines.
09:50Worse still, the plane has lost all conventional flight controls.
09:56Despite everything that Captain Haynes tries, the plane seems bent on turning over.
10:02Back in the cabin, the passengers feel the plane banking steeply.
10:07Now my son at seven and a half, he had always been a people watcher.
10:12And he looked around and he said, something's not right here.
10:17You could feel the turn.
10:19You could feel the sensation physically of your body leaning off to the right side.
10:23I remember feeling that and thinking that was very unusual.
10:283.18 p.m.
10:30The left wing is so high that the plane is in an extremely steep bank.
10:34Al Haynes knows that within a few more seconds, it will roll over and tumble out of control.
10:43There is just one old aviator's trick left to him.
10:46If it fails, flight 232 is doomed.
10:50The first reaction was to just close one throttle and push the other one up.
10:53See if maybe that would help.
10:54In a desperate bid to restore level flight, Haynes tries adjusting the relative power of the two wing engines.
11:02If the right engine runs faster, the airplane will bank left and vice versa.
11:12It works.
11:13Captain Haynes is able to pull the plane out of its roll.
11:17He still has no flight controls, but he regains a crude form of steering by using the throttles.
11:23But Haynes finds that he can only make right hand turns.
11:293.20 p.m.
11:32Co-pilot Bill Records radios Minneapolis Air Route Traffic Control Center.
11:39He reports the loss of flight controls and requests a flight path to the nearest airport.
11:46The pilots have no idea how they're going to land the crippled plane.
11:51Ladies and gentlemen, this is the captain. We've shut down the number two engine.
11:55Now Captain Haynes tells passengers that one engine has failed, but he doesn't mention the loss of flight controls.
12:03Not all the passengers find his words reassuring.
12:06You could just feel a tenseness in the flight attendants.
12:11And that's when you kind of felt, there's something not right here.
12:18Captain Haynes knows that time is running out.
12:23UA-232 is dropping at around 250 meters per minute.
12:29They need to attempt an emergency landing soon before they lose height altogether.
12:373.22. Air Traffic Control informs the flight crew that their nearest runway is at Sioux Gateway.
12:45This is a small regional airport near the sleepy town of Sioux City, Iowa.
12:523.25 p.m.
12:54A quiet afternoon in a Sioux City fire station is about to get a whole lot busier.
12:59When Fire Chief Robert Hamilton hears an alert called in, he suspects something big.
13:05I've been in this business a long time, and you can kind of tell.
13:08You have almost a sixth sense, I guess.
13:12Within minutes, the fire chief's hunch is proved correct.
13:15UA-232 is heading right for his city.
13:20Nine fire trucks race out to their emergency positions on one of the runways.
13:27Now Captain Haynes and his crew have to work out how they're going to land the plane with barely any
13:32controls.
13:36Before they can make a plan, they hit another problem.
13:39The DC-10 starts to soar up and then down in a random, uncontrollable cycle.
13:45For the pilots, it's like riding a roller coaster through the sky.
13:51I've got no idea how long I'm going to keep that airplane in the sky.
13:55Debbie McKelvey feels the plane's erratic motion and fears for her life.
14:00Here I have a six-year-old and a seven-year-old.
14:02You start praying, you know, if I'm going to die, please make sure we all go and we all go
14:06quick.
14:073.26 p.m.
14:09Captain Haynes calls his senior flight attendant up to the cockpit.
14:13When I opened that door, the whole atmosphere hit me.
14:17It's the worst crisis possible.
14:20The captain tells Jan to prepare the cabin for an emergency landing.
14:24As I walked through the first-class cabin, I just could not look anybody in the eye
14:29because I was afraid they'd read the fear in mine.
14:37Denny Fitch is a DC-10 training pilot flying home from an instructor session.
14:43He knows that something is wrong and offers his help.
14:483.29.
14:50What Denny finds in the cockpit shocks him.
14:54It was an amazing scene for me because both the pilots were, in fact, on the controls.
14:58Both of them, their tendons in their forearms were raised from effort.
15:02Their knuckles were white from grip.
15:08As an expert training pilot, Denny Fitch is ready for any emergency, but he's never seen anything like this before.
15:16I was dumbfounded because it was unheard of.
15:19As a matter of fact, there was no procedure for having no hydraulics.
15:22The first thought that came to my mind, to be honest, was that I was going to die that afternoon.
15:28Captain Haynes now tells his passengers the plane is damaged and they'll be making an emergency landing in Sioux City.
15:34This landing is a little different than you're used to.
15:37296 people could lose their lives.
15:40Getting this airplane down without crashing will be the ultimate test of pilot skill.
15:46Denny offers to help out any way he can.
15:49I said, Captain, would you want me to do your throttles?
15:52And he responded, yes, do that.
15:55Denny takes over on the throttles, the only controls still functioning.
16:01They allow him some degree of steering, but the plane is still only able to make right-hand turns.
16:12As far as I'm concerned, he's now the fourth member of the crew, because he was willing to step in
16:17there and help us any way he could.
16:203.48. The DC-10 is now 12 minutes from Sioux City Airport, and they're running out of altitude.
16:28It's time for the pilots to face an almost unthinkable prospect.
16:34In a few minutes, they must attempt to land a 165-ton jet without proper flight controls.
16:42The lives of 285 passengers are in their hands.
16:53The pilots must now try to line up for the final approach into Sioux City Airport.
16:59Denny Fitch will attempt to steer the plane and control its descent, all by adjusting the throttles.
17:06What's more, the plane can only make right-hand turns.
17:11The plan is to make a series of looping turns, and hope that as they come out of their final
17:17circuit, they're facing the runway.
17:21The odds are stacked against them.
17:25At 3.50 p.m., senior flight attendant Jan Brown-Law begins her final safety briefing.
17:32The passengers were right there in the palm of our hand.
17:36There, you could have heard a pin drop.
17:39Jan pays special attention to the four children too small to have their own seats.
17:43You need to put your seat belt on to cross.
17:47Official guidelines are nonspecific, but United Airlines procedure at the time is for adults to hold these lap children on
17:54the floor during an emergency landing.
17:59Jan is anxious about the procedure, but has no option but to follow protocol.
18:06It makes my skin crawl to this day to think that I found myself telling passengers, parents of lap children,
18:16to put their child on the floor and hold them down.
18:23As the flight crew near Sioux City, they are only too aware of what's at stake.
18:28You've got 296 lives in your two hands. You literally do.
18:33And I've never felt so overwhelmingly, you know, responsible for anything in my life.
18:41With no brakes, the DC-10 will need a long runway.
18:46Air traffic control assigns them runway 31 at 2,700 meters. It's the longest at Sioux City.
18:543.52 p.m.
18:56Denny Fitch puts the plane into its final looping turn.
19:00He knows the crippled jet would never be able to regain altitude for a second attempt.
19:05This was it. We had to land on that runway.
19:10One time. That's all we had.
19:13As they emerge from their final loop, the pilots see a wonderful sight.
19:18Sioux City Air Force, dead ahead.
19:21There's just one problem.
19:24It's the wrong runway.
19:27Here we are. There's a runway right in front of us. We're out of time. We're out of altitude.
19:31That's where we're going to go.
19:32Runway 22 is much shorter than runway 31.
19:36And it's full of fire trucks and ambulances.
19:40It wasn't until probably a couple of minutes at the most that we had a change in that.
19:46That the runway was actually shifted then from 1331 to runway 22.
19:523.59. Fire trucks race out of the path of the plunging DC-10.
19:58And so we were basically just kind of scrambling, getting out of the way, if you will, and trying to
20:03get to an ideal position for that particular runway.
20:09Captain Haynes orders the passengers into the brace position.
20:13Brace, brace, brace.
20:15The minute we said brace, it was like a breeze going over a field of wheat.
20:21Everybody in the cabin disappeared from sight to go into their brace position.
20:27I kept thinking, you know, this is it. And I actually made my son shut the window shade.
20:32And I thought, we don't need to see, you know, the end as it's coming.
20:42As the pilots desperately try to line up the airplane with the runway, they realize they're still coming in at
20:47400 kilometers per hour, around 150 kilometers per hour faster than normal.
20:53But with no control of the flaps, they cannot slow the descent.
21:01The alarm sounds from the ground proximity warning system.
21:04They're descending too rapidly.
21:07The plane is plunging at 560 meters per minute, over six times the normal rate.
21:18Down on the ground, a local news crew races into position to cover the crash landing.
21:23Not going to be pretty.
21:264 p.m.
21:28Just seconds from landing, the nose and right wing drop.
21:32If they come in at this angle, the plane could break apart.
21:36And I shoved both the throttles to maximum power, hoping that that would result in the nose being pulled up.
21:44Denny Fitch desperately struggles to bring the nose back up, but it's too late.
21:49The engines don't respond in time.
21:544 p.m. and 16 seconds, the plane smashes into the runway.
22:04It just felt like we dropped out of the sky and hit the ground.
22:06It wasn't like it was an emergency landing, it was a crash.
22:10I could hear all the screeching metal, the noises that you've never heard before and you hope you'll never hear
22:17again.
22:20The right landing gear and wing shear off, spilling fuel and sparking a fire.
22:26I could see fireballs because I guess the plane, you know, it's screeching on the runway.
22:33And then that was my next thought.
22:35Oh, my God.
22:37We're gonna burn to death.
22:41The jet careers along the runway on its wing stump for about 600 meters, then breaks apart.
22:51The cockpit had snapped off like a pencil tip and we became a tumbling 200-mile-an-hour piece of
22:57wreckage.
23:01The main section of the fuselage skids further down the runway, rolls over on its back and comes to a
23:07halt at the side of the airfield.
23:14The plane is split into three main pieces, cockpit, tail section and middle passenger section.
23:23Dozens of surviving passengers flee the burning cabin.
23:28Fire trucks and ambulances race to help them.
23:32Emergency workers arrive to an horrific scene of dead and injured passengers.
23:41Survivors escaping the wreckage scatter through cornfields at the edge of the runway.
23:46Debbie and her son Ryan are among them.
23:50I grabbed my son and we started running.
23:52And running.
23:53And I had no idea where we are.
23:55Some of the children and babies held on the floor before landing are missing.
24:00The violence of the crash tore them from their parents' grasp.
24:05One grief-stricken mother confronts flight attendant, Jan Brown Law.
24:10And she just looked up at me and she said,
24:12you told me to put him on the floor, that it would be alright.
24:16And I thought, I'm going to live with those words for the rest of my life.
24:21The child, 23-month-old Evan Zhao, tragically died in the burning jet.
24:28In the chaos of the crash, Debbie McKelvey and her son Ryan managed to get out of the wreck.
24:34But she can't see six-year-old daughter Devin anywhere.
24:38So then you start really thinking, why didn't I have both of them?
24:41And it's just a horrible, horrible sinking feeling.
24:49Jerry Schemmel escapes the cabin unhurt.
24:52But now he hears a baby's cries.
24:55Despite the choking fumes, he ventures back inside the burning aircraft.
25:01I didn't think if I go back in that thing will explode or I might not find my way back
25:05out.
25:05I just reacted. I heard the cries of baby and the next thing I know I'm back inside the aircraft.
25:10As the central cabin section burns, it starts to fill with toxic fumes.
25:15Smoke like this can kill in minutes.
25:19Parents like Debbie McKelvey fear that their missing children could still be somewhere inside the blazing jet.
25:30Flight 232 crashes at Sioux City Airport.
25:34And lies in a smoking ruin at the edge of the runway.
25:41Survivors flee the crashed airliner, but a baby's cries draw passenger Jerry Schemmel back inside.
25:47So I finally got right over top of the crying and I'm feeling around and there's a baby stuck inside
25:52this overhead bin.
25:53I just grabbed the baby with one arm and scooped her out of a hole.
25:56I got back on my feet, found the opening, just kind of aimed for the sunlight and shot out the
26:02plane the second time.
26:05Jerry's actions probably saved the baby's life.
26:08But Debbie McKelvey is desperate.
26:10She fears her daughter and friend have not survived the crash.
26:18Then, suddenly, she spots a face.
26:20It's her six-year-old daughter, Devon, emerging from the smoke.
26:24It was the absolute best feeling because she was there and she was okay.
26:34While passengers flee the wreckage, Captain Haynes and the flight crew are trapped in the cockpit.
26:41The plane's nose has buried itself into the soft earth beside the runway.
26:46It's the last place the rescuers reach.
26:50They have to use a forklift and cutting equipment to get through the twisted wreckage.
26:56It takes 30 minutes to reach the pilots.
27:01At 5 p.m., rescuers pull out all four pilots, seriously injured, but alive.
27:08I remember the pat on my chest and his words to me were,
27:12You're okay, buddy. I'm here. I got you. You're gonna be okay.
27:15And I felt this tremendous relief.
27:18The flaming wreck of UA-232 burns for over two hours.
27:27Nine helicopters and 34 ambulances evacuate survivors.
27:35Jerry Schemmel's thoughts turn to his buddy, Jay, whom he lost sight of in the crash.
27:42Jerry hopes that he might have made it, but as time goes by, he loses all hope.
27:47I had a pretty good hunch, eight hours after the crash, when he didn't show up anywhere, that he wasn't
27:52a survivor.
27:54Jay Ramsdell is one of 111 passengers who lose their lives in the crash.
28:00One flight attendant is also killed.
28:03Eleven children are among the dead.
28:09Remarkably, 184 people survived the Sioux City crash.
28:13But for the pilots of Flight 232, any number of deaths is a tragedy.
28:21Training pilot Denny Fitch learns how many died when his wife visits him in hospital.
28:32And she started crying because she realized I didn't know the truth.
28:35That, in fact, 112 people had died behind me.
28:39And when I saw her cry, I had my answer.
28:41And I cried every waking moment for the next three days.
28:45I just couldn't stop crying.
28:47It just so tore my heart out to know that people died behind me.
28:51I was ready to die for them, and I didn't want them to die.
28:55Al Haynes and the flight crew are determined that something positive should come out of the tragedy.
29:01I would like to say that this crew, and in fact the entire industry, is dedicated to finding the cause
29:08of this accident.
29:09So maybe we can never have it happen again.
29:18The National Transportation Safety Board, or NTSB, dispatches an investigation team to Sioux City.
29:26With 427 DC-10s still in service all around the world, they need to find out what happened to the
29:33plane, and quickly.
29:35Frank Hildrop leads the team, analyzing the aircraft structure.
29:40There's a lot of apprehension and anxiety, of course, that we always go into these things with, and it was
29:45fairly new at the time.
29:46I had not been with the agency, but for about nine months.
29:50Hildrop and the NTSB team arrive in Iowa nine hours after the crash, and get straight down to work.
29:58The investigators' first priority is to try to recover every piece of the wreckage, so that they can reassemble the
30:04aircraft.
30:06It's a mammoth task.
30:07It was such an immense accident scene that we just knew we had a long investigation ahead of ourselves.
30:16The crash scatters thousands of fragments of debris over a distance of one kilometer.
30:22Emergency services and the National Guard mobilize hundreds of personnel.
30:27They scour every square meter of land around the runway.
30:31The tiniest component might tell them what triggered the crash.
30:35As investigator Jim Wildey knows, only too well.
30:41If you want to understand how the airplane came apart, if you want to understand the interrelationships of various pieces,
30:48it is very useful sometimes to put the structure back together.
30:54Investigators interview the four pilots to explore the bizarre loss of controls they reported during the flight.
31:00Now we've lost all hydraulic pressure.
31:03Captain Haynes and the crew confirmed that shortly after the dramatic failure of their number two engine,
31:10all their hydraulic systems went down.
31:13It mystifies investigator Frank Hildrop.
31:18I know personally I wasn't prepared for dealing with an airplane crash where it had lost all of its hydraulics.
31:24An extremely unique event and something I personally had never encountered before.
31:29Hydraulics operate all the flight controls on the DC-10.
31:33The flaps that help control descent.
31:36The elevators that pitch the plane up and down.
31:40The rudder that steers it.
31:41The ailerons that make it bank.
31:44Pressurized fluid inside hydraulic lines operates these mechanical controls.
31:51There are three separate and independent hydraulic systems.
31:56Even if one system is breached, it should not cause the loss of hydraulic fluid in the others.
32:03To lose fluid from all three systems at once is almost impossible.
32:09Experts put the odds at a billion to one.
32:16Then, an unexpected find.
32:21Farmers 90 kilometers from Sioux City report aircraft wreckage scattered on their land.
32:29Investigators examine the debris and find that it includes components from the number two hydraulic system in the tail near
32:36the failed engine.
32:42The team can calculate from the plane's flight path exactly when these parts fell.
32:48They discover it happened at 3.16pm.
32:51The same moment as the loud bang and the engine failure.
32:59Everything points to a catastrophic event inside the engine, which then damages the hydraulic systems.
33:11They go back to the wrecked plane and examine every millimeter of its hydraulic lines.
33:16It's a painstaking process.
33:20But it pays off.
33:23They find puncture holes in the pressure lines of the plane's other two hydraulic systems.
33:28And the holes in both sets of pressure lines are near the failed engine.
33:34We determined that all the three hydraulic systems had been breached and that that's why the hydraulic fluid was lost
33:40and they lost the ability to really control the airplane.
33:43It's incredible, but true, something did put all three hydraulic systems out of action at exactly the same moment.
33:53But the team still has to prove that the number two engine caused the damage.
34:04They inspect the puncture holes with a scanning electron microscope.
34:10And find minute traces of titanium.
34:14Titanium is used for critical airplane parts because it's tough, yet very light.
34:19On the DC-10, the only titanium anywhere near the tail section is inside the number two engine.
34:30And when NTSB engineers reconstruct the DC-10's number two engine, a new clue confirms the team's theory.
34:41We learned that a major portion of the number two engine in the tail of the airplane had come apart
34:46and was missing.
34:47The missing part is the fan disc, the massive central hub of the engine's fan assembly.
34:53It's made of titanium.
34:58Investigators are starting to get a picture of what caused the bizarre loss of controls aboard flight UA-232.
35:0744 minutes from disaster.
35:11The loud bang that crew and passengers hear is the 170 kilogram fan disc fracturing.
35:19The broken fan disc bursts through the engine housing.
35:22The blast fractures a section of the number two hydraulic system.
35:27But in a piece of catastrophic bad luck, fragments also puncture lines in both remaining systems.
35:4342 minutes to go. The plane loses all its flight controls.
35:49The tail section is so badly damaged that the plane can only make right-hand turns.
35:56And without elevators, the pilots cannot keep the plane on a level flight path through the sky.
36:05But the NTSB investigators still don't know what caused the fan disc to fracture.
36:15Until they find out, more than 200 other DC-10s could be flying around with engines that have a similar
36:21hidden fault.
36:32They must locate and examine the missing pieces of fan disc.
36:42Investigators calculate the likely trajectory of the fan disc debris to find out where it might have landed.
36:48They narrow it down to a track of Iowa Corn Belt 36 square kilometers in size.
36:54I would consider the search for that fan disc certainly a needle in a haystack type of effort.
37:01Investigators pull out all the stops to find the missing fan disc.
37:05They scour the area with four helicopters, but find that the three-meter-high corn stalks conceal everything on the
37:12ground.
37:14They even deploy infrared cameras to try to locate the pieces.
37:21But after weeks of searching, they draw a blank.
37:26General Electric, the engine manufacturer, offers members of the public a large reward for the missing fan disc.
37:36But there's still no sign of it.
37:43Two months go by and harvest time comes around.
37:49Janice and Dale Sorensen have a 180-hectare farm right in the middle of the search area.
37:56Tuesday, October 10th, 1989, and Janice Sorensen is out bringing in the corn.
38:03As I was combining, I felt a little resistance on the front of the combine.
38:09And I backed it up and then put it in neutral and got out and looked and I knew immediately
38:16that this was the piece they were looking for.
38:20It's a massive chunk of debris, half buried in the earth.
38:27Teams from General Electric and the NTSB race to the Sorensen farm.
38:38Dale and Janice help investigators dig out the piece of wreckage.
38:42This is the Sorensen's own video footage of their find.
38:47I had a little shovel long and I went and got the tractor with a loader and put a chain
38:53around it and hoisted it up.
38:54And then we took it down to the turkey shed, which was not very far away.
39:00And we had hot water there, so we washed it off, so it was a spick and span.
39:05Investigators quickly confirm that the debris is a major chunk of the missing fan disc from flight UA-232.
39:13Then, they find another piece nearby.
39:17Together, the two parts complete the entire missing fan disc.
39:24Janice Sorensen learns that her find could hold the key to the disaster.
39:30I was very emotional about it.
39:31I had some tears.
39:33It was a combination of the excitement of finding the piece and the tears for those who'd lost their lives.
39:41Janice and her husband Dale collect General Electric's $120,000 reward.
39:47They give over half the money to charity.
39:51The NTSB can now begin the next phase of their investigation.
39:57They fly the fractured fan disc to the labs of the engine manufacturer General Electric
40:03to find out what could break apart such a robust metal component.
40:10Jim Wildey, a metallurgist by training, examines the fan disc, starting with the main fracture line where it broke apart.
40:19He spots something branching off it.
40:20A fatigue crack, 13 millimeters long.
40:25It's rare to find metal fatigue in a fan disc.
40:28These components are specifically designed to withstand the enormous rotational forces within the engine.
40:38Then, at the base of the fatigue crack, Wildey sees a tiny cavity.
40:44The size of it was maximum in any one direction was about 50 thousandths of an inch.
40:50As he scans the cavity more closely, he sees that the metal around it looks discolored.
40:56He takes a sample from this suspect area for testing.
41:01What he discovers will shock the investigation team and rock the aviation industry to its core.
41:14Investigator Jim Wildey examines a tiny cavity in the fractured fan disc from flight UA-232.
41:24What he finds stunts him.
41:26Around the cavity, there is an impurity in the titanium alloy.
41:33It's called a hard alpha inclusion, a brittle defect smaller than a fingernail.
41:41Analysis reveals that it was caused by excess nitrogen during the forging of the metal ingot.
41:50The fan disc in the DC-10 was made from titanium that harbored a fatal hidden defect.
41:59It's the final piece of the puzzle.
42:04The NTSB team can now put together the chain of events that left the passengers and crew of flight UA
42:10-232 seconds from disaster.
42:20As the DC-10's fan disc rotates at 3,800 RPM, the huge stresses initiate a minute crack in the
42:28defect.
42:31With every flight, it grows fractionally bigger.
42:36July 19th, 1989, 44 minutes from disaster.
42:41The fan disc has been in service for 15,503 flights over 17 years.
42:50The crack reaches 13 millimeters in length.
42:54The faulty fan disc can no longer cope with the stresses imposed by its rotation.
42:59It shears in too.
43:04The damage it causes makes the DC-10 virtually unflyable.
43:11For the next 40 minutes, the pilots struggle to control the plane.
43:20Five minutes to go.
43:22Flight 232 comes out of its final turn into Sioux City.
43:3020 seconds.
43:32As the plane comes in to land, the right wing drops.
43:42Disaster strikes.
43:43The right wing tip hits the ground, and the DC-10 careers down the runway.
43:53A 21 million dollar jet, weighing 165 tons, is brought down by a tiny metallic floor.
44:03For the NTSB investigation team, there's a terrible twist to the tragedy.
44:11Investigators discover that United Airlines technicians made a routine inspection of the defective fan disc just 16 months before the
44:19crash.
44:20They are disturbed.
44:22The crack was on the fan disc surface.
44:24At the time of the inspection, the crack could have been close to 13 millimeters long.
44:29This disc had been inspected before the accident, and we determined that the crack was of a detectable size, but
44:37that it just wasn't detected.
44:39The NTSB report concluded that the crack was probably missed due to human error.
44:48The report accepted that United Airlines inspection procedures complied with regulations and were up to industry standard,
44:56and cited human factors as an industry-wide problem in engine inspection.
45:04In the wake of the Sioux City disaster, the Federal Aviation Authority upgraded engine inspection procedures.
45:14The FAA also demanded changes to the DC-10's hydraulic systems.
45:19Airlines were required to add shut-off valves to limit the amount of fluid that can drain from a breach
45:25in hydraulic lines.
45:28But today, lab children are still allowed to remain unrestrained during emergency landings.
45:38Ever since the crash, Jam Brown Law has campaigned for all children to have allocated seats and safety restraints on
45:46airplanes.
45:47She has never forgotten the young boy, Evan Zhao, who lost his life on her watch.
45:53Evan would be 17 years old today, had he been in a seat.
45:59Denny Fitch, Al Haynes, and the other crew members received industry awards for their extraordinary professionalism and valor.
46:09Jerry Schemmel, who now has children of his own, will never forget the debt he owes the pilots.
46:16I've thought about those guys every day for 16 years.
46:19I don't think we could have been equipped with a better copy crew than what we had.
46:26The safety measures triggered by the Sioux City crash transformed aviation safety, not just on the DC-10, but on
46:34all passenger airliners.
46:37The new rules should ensure that such a bizarre and devastating accident can never happen again.
46:58The safety measures against each other will seem much worse than the Links irgendetrics.
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