1 00:00:01,455 --> 00:00:02,355 ANNOUNCER: This program is rated PG, and contains 2 00:00:02,355 --> 00:00:02,455 ANNOUNCER: This program is rated PG, and contains 3 00:00:02,500 --> 00:00:05,060 ANNOUNCER: This program is rated PG, and contains 4 00:00:05,060 --> 00:00:06,200 mature subject matter. 5 00:00:06,200 --> 00:00:07,660 Viewer discretion is advised. 6 00:00:28,070 --> 00:00:30,970 NARRATOR: An airplane loaded with passengers is going down... 7 00:00:35,394 --> 00:00:41,336 ATC: He's coming down real fast. 8 00:00:41,470 --> 00:00:43,070 I remember hearing a lot of screaming, 9 00:00:43,390 --> 00:00:44,890 a lot of panic and a lot of chaos. 10 00:00:55,600 --> 00:00:57,820 MAN: But what caused it to crash? 11 00:00:59,039 --> 00:01:02,480 This wasn't a bomb, it wasn't a bird strike. 12 00:01:02,700 --> 00:01:06,320 What happened up there at 37,000ft 13 00:01:06,320 --> 00:01:09,040 that rendered this airplane uncontrollable. 14 00:01:09,260 --> 00:01:13,120 SIAN: Now... engineers unlock the clues 15 00:01:13,120 --> 00:01:14,900 to the world's biggest disasters... 16 00:01:24,150 --> 00:01:27,830 ... to find out what happens when big things go wrong. 17 00:01:28,610 --> 00:01:33,270 These are the ultimate fears that keep structural engineers awake at night. 18 00:01:41,793 --> 00:01:43,957 MAN: Oh, my God! 19 00:01:52,979 --> 00:01:56,159 NARRATOR: Dawn. Denver Stapleton International Airport. 20 00:01:56,780 --> 00:01:59,079 Thousands of passengers wait to board flights. 21 00:01:59,559 --> 00:02:02,199 Among them, is sports caster Jerry Schemmel. 22 00:02:02,659 --> 00:02:05,780 You know it seemed like a normal day, it really did. 23 00:02:06,320 --> 00:02:09,139 I remember getting to the airport about six o' clock in the morning 24 00:02:09,299 --> 00:02:11,019 and we found out our flight was cancelled. 25 00:02:11,740 --> 00:02:13,758 And so we got put on standby status 26 00:02:13,939 --> 00:02:17,319 and finally maybe close to six hours after originally supposed to fly, 27 00:02:17,639 --> 00:02:20,680 got on United Flight 232 that took off to Chicago. 28 00:02:23,299 --> 00:02:26,639 NARRATOR: At 1.45 pm, Jerry heads to his seat. 29 00:02:28,039 --> 00:02:29,899 We were the last to board the aircraft, 30 00:02:30,259 --> 00:02:33,240 I remember walking that plane thinking to myself "Well this is a big plane." 31 00:02:33,780 --> 00:02:35,840 NARRATOR: Almost 20 years after its launch, 32 00:02:36,419 --> 00:02:40,300 the DC-10 remains one of the largest passenger jets in the sky. 33 00:02:41,180 --> 00:02:42,959 It's also highly distinctive. 34 00:02:43,820 --> 00:02:48,340 The DC 10 is one of the most iconic airplanes of the '70s and 80's 35 00:02:48,600 --> 00:02:51,240 because of its characteristic three engine structure, 36 00:02:51,380 --> 00:02:54,519 it's got two engines under the wing and one over the tail. 37 00:02:55,199 --> 00:02:58,399 NARRATOR: Today, as United flight 232 leaves Denver, 38 00:02:58,659 --> 00:03:01,579 it's carrying 296 passengers and crew. 39 00:03:01,819 --> 00:03:04,139 But none of them know they are heading for disaster. 40 00:03:05,501 --> 00:03:08,679 (CLOCK TICKING) 41 00:03:08,809 --> 00:03:11,349 First hour was routine, it really was. 42 00:03:11,869 --> 00:03:12,909 it was a smooth flight, 43 00:03:12,950 --> 00:03:15,589 I remember that everything seemed normal, 44 00:03:16,049 --> 00:03:17,489 nothing out of the ordinary at all. 45 00:03:19,108 --> 00:03:22,548 (CLOCK TICKING) 46 00:03:22,680 --> 00:03:25,100 JERRY: The flight attendants were picking up the lunch 47 00:03:25,100 --> 00:03:28,700 and the trays and all that, I'm thinking, it's a normal flight. 48 00:03:29,939 --> 00:03:30,939 NARRATOR: Seconds later... 49 00:03:38,800 --> 00:03:41,040 I thought a terrorist had planted a bomb, 50 00:03:41,540 --> 00:03:43,640 it's been detonated and we're going down 51 00:03:43,800 --> 00:03:47,280 and everybody is gonna die here in the next whatever it takes to hit the ground. 52 00:03:47,939 --> 00:03:51,000 I remember hearing screaming, a lot of panic, a lot of chaos. 53 00:03:51,640 --> 00:03:54,740 NARRATOR: But the explosion is only the start of their ordeal. 54 00:03:55,620 --> 00:03:57,960 The blast damages critical flight controls. 55 00:04:02,364 --> 00:04:09,342 (CLOCK TICKING) 56 00:04:09,479 --> 00:04:12,340 NARRATOR: By a stroke of luck, on board is Denny Fitch 57 00:04:12,940 --> 00:04:16,480 a flight instructor who has clocked over 23,000 hours flying 58 00:04:17,019 --> 00:04:18,339 including in a DC10. 59 00:04:19,000 --> 00:04:22,480 He helps the two pilots regain some control of the plane. 60 00:04:23,040 --> 00:04:26,279 Denny Fitch and Captain Haynes have to reinvent the wheel 61 00:04:26,279 --> 00:04:27,860 in order to land this plane. 62 00:04:28,079 --> 00:04:31,360 It can only turn to the right and so as they're circling 63 00:04:31,580 --> 00:04:32,920 they're going down at elevation. 64 00:04:32,920 --> 00:04:36,360 That means they have only one shot to get it right. 65 00:04:58,920 --> 00:05:01,560 NARRATOR: The crew aims for Sioux City, Iowa. 66 00:05:02,340 --> 00:05:04,220 JERRY: Captain Haynes is on the PA system, 67 00:05:04,520 --> 00:05:07,860 he said I want everybody to understand this is going to be rough. 68 00:05:08,000 --> 00:05:10,980 This is not gonna be a landing where we're gonna land safely 69 00:05:11,040 --> 00:05:12,180 and you're gonna walk off the plane, 70 00:05:12,380 --> 00:05:14,020 this is going to be a crash landing. 71 00:05:17,180 --> 00:05:20,020 NARRATOR: Against all odds, they line up with the runway. 72 00:05:21,320 --> 00:05:23,400 I got in that brace position right away, 73 00:05:23,580 --> 00:05:25,580 and I just waited and waited, 74 00:05:25,800 --> 00:05:28,680 and thinking to myself, man 30 seconds is a long time. 75 00:05:29,699 --> 00:05:32,561 (CLOCK TICKING) 76 00:05:39,500 --> 00:05:45,919 NARRATOR: The DC 10 is descending at 255MPH, twice as fast as it should be. 77 00:05:51,649 --> 00:05:54,649 I was not ready for how hard we hit. 78 00:05:54,929 --> 00:05:57,609 It just sort of felt like we dropped out of the sky and hit the ground. 79 00:05:58,509 --> 00:06:01,734 (CLOCK TICKING) 80 00:06:01,850 --> 00:06:04,570 NARRATOR: The airplane's wing hits the runway first... 81 00:06:05,490 --> 00:06:09,330 Fuel ignites. the aircraft breaks in two... 82 00:06:10,189 --> 00:06:12,250 The biggest section skids off the runway 83 00:06:12,810 --> 00:06:14,810 ending up upside-down in a cornfield. 84 00:06:17,050 --> 00:06:19,530 One hundred and twelve people die in the crash. 85 00:06:20,110 --> 00:06:22,670 It's one of America's deadliest air disasters. 86 00:06:23,510 --> 00:06:27,250 This wasn't a bomb, it wasn't a bird strike. 87 00:06:27,570 --> 00:06:31,210 Something happened up there thousands of feet up 88 00:06:31,210 --> 00:06:34,310 that rendered this airplane uncontrollable. 89 00:06:34,490 --> 00:06:36,970 What brought down this DC10? 90 00:06:37,470 --> 00:06:38,830 And could it happen again? 91 00:06:39,730 --> 00:06:41,690 NARRATOR: The roots of this mystery lie in events 92 00:06:41,690 --> 00:06:43,770 before the plane even hits the runway... 93 00:06:50,800 --> 00:06:52,360 It's 1965. 94 00:06:53,259 --> 00:06:56,660 With the economy booming, air-travel is growing fast 95 00:06:57,060 --> 00:06:59,579 and passenger numbers are doubling every ten years. 96 00:07:00,139 --> 00:07:04,220 In response McDonnell-Douglas design the massive DC10 97 00:07:04,220 --> 00:07:05,620 to carry more customers. 98 00:07:06,960 --> 00:07:09,820 The first design proposals for the DC10 99 00:07:09,820 --> 00:07:12,860 were for a wide-bodied double decker airliner 100 00:07:12,860 --> 00:07:17,699 with four engines capable of carrying 550 passengers. 101 00:07:18,500 --> 00:07:21,300 But that was just too ambitious, too aggressive, 102 00:07:21,300 --> 00:07:23,800 it was paired down into what we see. 103 00:07:23,900 --> 00:07:26,920 Which is the three engines, a single level 104 00:07:27,160 --> 00:07:29,960 and it was a very very useful plane. 105 00:07:30,639 --> 00:07:33,439 NARRATOR: The DC-10 is a state-of-the art aircraft 106 00:07:33,600 --> 00:07:36,439 and its construction calls for the latest materials. 107 00:07:37,340 --> 00:07:39,580 One very strong metal in particular... 108 00:07:40,640 --> 00:07:41,640 Titanium. 109 00:07:41,840 --> 00:07:45,319 For high stress applications requiring a strong metal, 110 00:07:45,700 --> 00:07:47,939 there's no substitute for titanium. 111 00:07:48,480 --> 00:07:51,480 While the strength of steel in on a par with titanium, 112 00:07:51,800 --> 00:07:54,199 it weighs 45 percent more. 113 00:07:55,379 --> 00:07:58,340 Titanium appears almost indestructible. 114 00:07:59,020 --> 00:08:00,860 NARRATOR: It's perfect for jet-engine parts... 115 00:08:01,260 --> 00:08:02,560 Like a fan disc. 116 00:08:04,240 --> 00:08:05,920 Set deep inside the engine, 117 00:08:06,940 --> 00:08:10,200 a fan disc produces most of the thrust needed for flight. 118 00:08:11,200 --> 00:08:13,819 Spinning at 3,800 revolutions per minute, 119 00:08:14,660 --> 00:08:17,600 it experiences immense stress when in use. 120 00:08:17,820 --> 00:08:19,540 So it has to be tough. 121 00:08:20,260 --> 00:08:22,520 To construct aviation components out of titanium, 122 00:08:22,639 --> 00:08:25,080 you have to start with a raw material. This is called a billet. 123 00:08:25,420 --> 00:08:27,560 NARRATOR: These are huge pieces of metal alloy, 124 00:08:27,560 --> 00:08:29,320 forged in extreme heat. 125 00:08:30,060 --> 00:08:32,100 Before shipping, each billet undergoes 126 00:08:32,100 --> 00:08:34,640 ultrasonic inspection to look for any defects. 127 00:08:35,559 --> 00:08:38,019 If there are defects within the billet, 128 00:08:38,200 --> 00:08:42,600 those defects get carried along into whatever component you're manufacturing. 129 00:08:43,020 --> 00:08:46,899 NARRATOR: In a factory mistake, one billet escapes the safety check. 130 00:08:47,340 --> 00:08:51,700 And the first clue to the United 232 disaster lies within it. 131 00:08:59,000 --> 00:09:01,740 It's a flaw no bigger than a grain of sand. 132 00:09:02,340 --> 00:09:06,039 Hidden just below the surface of the 7000-pound billet. 133 00:09:08,000 --> 00:09:11,519 It's then sent to Ohio, where it's disk.into a fan 134 00:09:11,920 --> 00:09:14,700 And fitted into the most critical part of the airframe... 135 00:09:15,120 --> 00:09:17,700 The tail-engine of the Sioux City jet. 136 00:09:18,340 --> 00:09:21,240 A deadly crack now lies in the heart of the plane. 137 00:09:22,159 --> 00:09:25,860 No-one knew that this microscopic anomaly was in this fan disc. 138 00:09:27,059 --> 00:09:30,539 NARRATOR: Even the smallest defects can bring down the biggest machines. 139 00:09:31,299 --> 00:09:35,220 As space shuttle engineers discover in Florida, in 1986. 140 00:09:40,310 --> 00:09:41,550 NARRATOR: Like the DC-10, 141 00:09:42,050 --> 00:09:45,590 a weakness lies within the 1.2- billion-dollar spacecraft. 142 00:09:46,390 --> 00:09:48,190 ARCHIVE: T minus three minutes and counting 143 00:09:48,890 --> 00:09:52,690 NARRATOR: January 28th, and the Challenger shuttle prepares for blast off. 144 00:09:52,950 --> 00:09:54,650 ARCHIVE: Gimbal checks now complete. 145 00:09:55,110 --> 00:09:59,830 On board, seven crew members, including high- school teacher, Christa McAuliffe. 146 00:10:00,250 --> 00:10:01,890 ARCHIVE: T minus two minutes and counting 147 00:10:02,450 --> 00:10:05,690 She's the first US civilian selected to go into space. 148 00:10:06,930 --> 00:10:10,810 Key to lift-off, rocket boosters on both sides of the shuttle, 149 00:10:10,810 --> 00:10:13,870 packed with 500 tons of explosive fuel. 150 00:10:15,170 --> 00:10:17,910 NARRATOR: Rubber O-rings, just a quarter of an inch thick, 151 00:10:18,090 --> 00:10:20,950 are all that seal in the highly flammable gas. 152 00:10:21,310 --> 00:10:22,770 ARCHIVE: Ninety seconds and counting. 153 00:10:23,530 --> 00:10:26,129 A "O" ring is squishy so that, when you press on it, 154 00:10:26,509 --> 00:10:29,490 it deforms and fills all the microscopic gaps 155 00:10:29,490 --> 00:10:31,450 between the two materials you're pressing together. 156 00:10:31,630 --> 00:10:34,970 And that now, does not allow any gas to get out or any liquid. 157 00:10:35,104 --> 00:10:37,474 ARCHIVE: T minus 45 seconds and counting. 158 00:10:37,606 --> 00:10:39,676 Sounds of pressure and water system now armed. 159 00:10:39,810 --> 00:10:42,210 Because the O Rings are basically a form of rubber 160 00:10:42,490 --> 00:10:44,769 you've got to be careful when it comes to temperature. 161 00:10:45,150 --> 00:10:49,250 If it's too cold it changes how that material reacts. 162 00:10:51,010 --> 00:10:54,590 NARRATOR: O-rings work best at temperatures above 64 degrees. 163 00:10:55,690 --> 00:10:58,870 But on launch day, it's a chilly 36 degrees. 164 00:11:01,010 --> 00:11:03,890 Take a donut, right? As soon as you buy a donut, 165 00:11:03,970 --> 00:11:05,270 it's nice and squishy. It's soft. 166 00:11:05,450 --> 00:11:06,450 It's at room temperature. 167 00:11:06,810 --> 00:11:08,810 Stick the donut in the refrigerator overnight. 168 00:11:08,970 --> 00:11:10,650 Now pick it up, it's crispy, right? 169 00:11:10,710 --> 00:11:12,790 It's just like more brittle and it's tough. 170 00:11:12,910 --> 00:11:16,970 ARCHIVE: T minus 30 seconds, we've had a go for auto sequence start. 171 00:11:17,250 --> 00:11:20,090 NARRATOR: Engineers flag their concerns about the O-rings performance 172 00:11:20,090 --> 00:11:22,310 in the cold and try to stop the launch. 173 00:11:23,250 --> 00:11:25,370 But NASA proceeds anyway. 174 00:11:26,250 --> 00:11:29,230 ARCHIVE: The SRB hydraulic power units have started. 175 00:11:30,269 --> 00:11:33,950 The first evidence of a potential abnormality 176 00:11:33,950 --> 00:11:37,810 is in the form of black smoke that's just puffing out 177 00:11:37,810 --> 00:11:41,330 right above a seal where an O Ring would be. 178 00:11:41,467 --> 00:11:44,219 INAUDIBLE RADIO: T minus 10... 179 00:11:44,356 --> 00:11:49,172 That's an indication that high pressure gas is getting through that seal 180 00:11:49,310 --> 00:11:51,950 and as the gas gets through, it starts to open up even more. 181 00:11:53,382 --> 00:11:57,676 ARCHIVE: Three. Two. One. 182 00:11:57,676 --> 00:12:00,036 And lift off on the 25th space shuttle mission, 183 00:12:00,280 --> 00:12:01,660 and it has cleared the tower. 184 00:12:03,759 --> 00:12:05,300 Challenger go with throttle up. 185 00:12:05,340 --> 00:12:08,040 NARRATOR: Nobody in mission control spots the smoke. 186 00:12:08,759 --> 00:12:10,899 Challenger has passed the point of no return. 187 00:12:11,720 --> 00:12:13,139 Disaster is inevitable. 188 00:12:13,820 --> 00:12:15,380 You end up with a major failure, 189 00:12:15,780 --> 00:12:18,779 where the fuel was blowing out of the sides 190 00:12:18,779 --> 00:12:19,860 and the whole thing blew apart. 191 00:12:22,253 --> 00:12:24,881 (EXPLOSION) 192 00:12:31,899 --> 00:12:34,059 NARRATOR: The world watches in horror. 193 00:12:37,549 --> 00:12:39,129 ARCHIVE: Obviously a major malfunction. 194 00:12:41,600 --> 00:12:42,960 We have no down link. 195 00:12:44,160 --> 00:12:46,840 NARRATOR: One of the most complex machines ever built, 196 00:12:47,220 --> 00:12:49,160 brought down by a quarter inch part. 197 00:12:51,710 --> 00:12:54,290 Like Challenger, the Sioux City DC-10 198 00:12:54,290 --> 00:12:56,770 is fatally compromised by a hidden mistake. 199 00:12:59,350 --> 00:13:02,470 In a highly engineered piece of equipment like an airplane, 200 00:13:02,889 --> 00:13:05,009 the very small details really matter 201 00:13:05,090 --> 00:13:08,330 and it only takes one tiny little failure to cause a catastrophe. 202 00:13:09,170 --> 00:13:12,509 NARRATOR: Coming up. Other clues to why it crashed... 203 00:13:12,970 --> 00:13:15,310 The thought of all three failing at once 204 00:13:15,930 --> 00:13:18,030 was inherently possible, 205 00:13:18,230 --> 00:13:20,690 but was waved off as not gonna happen. 206 00:13:21,230 --> 00:13:24,010 NARRATOR: And later, a Dakota train crash shows 207 00:13:24,010 --> 00:13:26,710 what can happen when warning signs are ignored. 208 00:13:46,000 --> 00:13:48,000 NARRATOR: When big things go wrong, 209 00:13:48,440 --> 00:13:50,040 engineers must find out why. 210 00:13:59,850 --> 00:14:01,870 In the case of the Sioux City plane. 211 00:14:02,250 --> 00:14:05,970 One clue is a microscopic defect in the fan disk. 212 00:14:06,450 --> 00:14:11,509 These cracks are virtually invisible to the untrained eye 213 00:14:11,630 --> 00:14:15,270 and they are extremely hard to detect to the trained eye. 214 00:14:15,610 --> 00:14:18,970 NARRATOR: But the plane flies for 17 years without incident. 215 00:14:19,450 --> 00:14:21,930 So what else could explain this disaster? 216 00:14:32,100 --> 00:14:34,580 All aircraft undergo regular maintenance 217 00:14:34,580 --> 00:14:37,019 and the Sioux City DC-10 is no exception. 218 00:14:39,549 --> 00:14:43,169 Its three jet engines clock up 42,000 flight hours, 219 00:14:43,789 --> 00:14:47,449 and with each flight, the tail engine edges closer to failure. 220 00:14:48,089 --> 00:14:49,910 Every time the engine was started 221 00:14:50,069 --> 00:14:52,990 the crack would grow a little bit more from the cavity, 222 00:14:53,189 --> 00:14:54,289 just a fraction. 223 00:14:55,209 --> 00:14:56,530 We call it a fatigue crack 224 00:14:56,930 --> 00:14:59,390 and it's started to grow and progress 225 00:14:59,390 --> 00:15:01,209 over the lifetime of the engine. 226 00:15:01,870 --> 00:15:03,519 DR. HENRY: Now this crack starts spreading 227 00:15:03,519 --> 00:15:06,250 and starts growing and getting deeper and deeper into the material, 228 00:15:06,810 --> 00:15:08,910 weakening this component. And you have no idea. 229 00:15:09,549 --> 00:15:11,969 NARRATOR: Engineers carry out six major inspections 230 00:15:11,969 --> 00:15:16,469 during the aircraft's lifetime, but every time they miss the flaw. 231 00:15:17,509 --> 00:15:19,949 It was so small that it wasn't really considered 232 00:15:20,050 --> 00:15:23,310 and the whole system was designed to detect these larger cracks 233 00:15:23,310 --> 00:15:24,750 and these larger anomalies. 234 00:15:24,929 --> 00:15:26,789 In this instance it was just so small 235 00:15:26,789 --> 00:15:30,990 that it went undetected during the ultrasonic testing of that time. 236 00:15:32,750 --> 00:15:35,190 NARRATOR: By the final inspection in 1989, 237 00:15:35,670 --> 00:15:37,209 just months before the crash, 238 00:15:37,209 --> 00:15:41,390 the cavity in the engine has grown into a crack about half an inch long. 239 00:15:41,890 --> 00:15:43,390 And it's still missed. 240 00:15:43,770 --> 00:15:46,310 There would come a point where it had grown enough, 241 00:15:46,310 --> 00:15:52,109 that one more start of the engine would result in it breaking and smashing out. 242 00:15:53,190 --> 00:15:56,310 NARRATOR: Now every flight is a potential disaster. 243 00:15:58,009 --> 00:16:01,189 Unseen cracks can grow and may eventually snap. 244 00:16:02,390 --> 00:16:04,969 When they do, they create havoc. 245 00:16:05,510 --> 00:16:08,150 As the drivers of two huge freight trains discover. 246 00:16:11,600 --> 00:16:13,460 NARRATOR: On the North Dakota plains... 247 00:16:14,360 --> 00:16:18,019 A train's axle has slowly grown a micro-crack over 11 years. 248 00:16:19,240 --> 00:16:21,020 Just like with the DC10, 249 00:16:21,540 --> 00:16:24,380 routine inspections and maintenance have failed to spot it. 250 00:16:25,320 --> 00:16:30,300 And when it breaks, disaster strikes, causing a catastrophic collision. 251 00:16:54,809 --> 00:16:56,250 NARRATOR: Two billion tons of freight moves 252 00:16:56,250 --> 00:16:58,310 across America's rail-lines every year. 253 00:16:59,990 --> 00:17:02,650 And all that cargo calls for big trains. 254 00:17:04,509 --> 00:17:10,409 December 30th, 2013, a 104-car train travels west, 255 00:17:10,409 --> 00:17:13,270 through the city of Casselton. Loaded with grain. 256 00:17:16,849 --> 00:17:20,750 The steel axle of one of the cars has a tiny fatigue crack. 257 00:17:20,750 --> 00:17:24,189 Hidden in the metal since it was manufactured over a decade ago. 258 00:17:25,750 --> 00:17:28,789 One and a quarter inches long, the crack is growing 259 00:17:29,089 --> 00:17:32,628 and, as it weakens, the axle begins to bend. 260 00:17:33,949 --> 00:17:37,730 Imagine you gotta piece of rope and deep inside the rope 261 00:17:37,730 --> 00:17:39,510 is like a little shard of glass. 262 00:17:39,869 --> 00:17:41,889 And so now as you start using the rope 263 00:17:41,889 --> 00:17:43,069 and you're working with the rope, 264 00:17:43,329 --> 00:17:45,569 you're moving it around and that little shard of glass 265 00:17:45,569 --> 00:17:47,730 is gonna start cutting the tendons of that rope, 266 00:17:48,069 --> 00:17:50,050 making it weaker and weaker, but you can't tell 267 00:17:50,050 --> 00:17:51,649 cause you're looking at the outside of the rope. 268 00:17:53,108 --> 00:17:56,250 NARRATOR: Around 2.08pm, it finally snaps. 269 00:18:00,849 --> 00:18:03,390 Broken pieces of steel tumble under the train 270 00:18:03,390 --> 00:18:05,370 and derail some of the cars behind. 271 00:18:06,570 --> 00:18:09,770 But the train is so long its driver has no idea. 272 00:18:13,550 --> 00:18:16,750 And coming the other way, another train, 273 00:18:16,750 --> 00:18:18,889 pulling the worst possible cargo. 274 00:18:20,870 --> 00:18:24,490 Over two million gallons of combustible crude oil. 275 00:18:28,000 --> 00:18:31,760 By the time the driver of the oil train sees the derailed car, 276 00:18:32,220 --> 00:18:33,220 it's too late. 277 00:18:40,650 --> 00:18:43,470 You've got metal wheels in contact with a metal rail, 278 00:18:43,950 --> 00:18:46,310 so you've got plenty of friction and a source for a spark, 279 00:18:46,730 --> 00:18:48,830 and a spark goes off and lights the whole thing up. 280 00:18:54,750 --> 00:19:00,109 NARRATOR: The fireball spews toxic gasses and burns for 24 hours. 281 00:19:01,469 --> 00:19:04,390 It's sheer luck that nobody dies in this disaster. 282 00:19:08,950 --> 00:19:11,850 Coming up... More clues uncovered. 283 00:19:12,309 --> 00:19:13,990 The pilots don't know what's going on, 284 00:19:14,090 --> 00:19:16,250 but something is very, very wrong with the aircraft. 285 00:19:18,950 --> 00:19:23,309 NARRATOR: And more shocking disasters when big things go wrong. 286 00:19:37,050 --> 00:19:39,610 NARRATOR: A DC10 aircraft has crashed, 287 00:19:39,909 --> 00:19:41,389 killing half those on board. 288 00:19:41,970 --> 00:19:44,869 The survivors start to come to terms with their ordeal. 289 00:19:45,669 --> 00:19:47,149 I don't even know what happened, 290 00:19:47,269 --> 00:19:50,129 I didn't even know we were upside down until I let go of my seatbelt. 291 00:19:50,409 --> 00:19:52,769 We went to the wing and slid down into the corn field. 292 00:19:52,936 --> 00:19:56,840 To be unscathed is a miracle. 293 00:19:57,009 --> 00:19:59,629 NARRATOR: Investigators now examine the wreckage looking for answers 294 00:19:59,930 --> 00:20:02,869 but with vital components strewn across Iowa, 295 00:20:03,309 --> 00:20:04,609 it's a difficult task. 296 00:20:05,509 --> 00:20:08,490 MAN: That whole fan area is missing! 297 00:20:09,049 --> 00:20:12,509 NARRATOR: The next piece to the puzzle lies somewhere surprising. 298 00:20:22,150 --> 00:20:25,269 NARRATOR: In 1968 when planning the DC-10, 299 00:20:25,750 --> 00:20:27,750 its manufacturers, McDonnell-Douglas, 300 00:20:27,990 --> 00:20:29,810 consider the growing domestic market. 301 00:20:30,730 --> 00:20:33,450 With the right plane, a fortune could be made. 302 00:20:34,190 --> 00:20:37,890 The company needs a plane with longer range than two-engined jets, 303 00:20:38,090 --> 00:20:41,390 but with lower operating costs than its four-engined rivals. 304 00:20:42,370 --> 00:20:44,090 The engines of the time, the jet engines, 305 00:20:44,170 --> 00:20:45,610 didn't have enough thrust to only use 2. 306 00:20:45,950 --> 00:20:48,250 The optimal solution then is to have three engines, 307 00:20:48,290 --> 00:20:49,590 but where do you put the third engine? 308 00:20:49,750 --> 00:20:52,230 You can't have two engines on one side and one on the other. 309 00:20:52,490 --> 00:20:54,390 So, the solution was to put the third engine 310 00:20:54,390 --> 00:20:56,750 on top of the airplane in the tail. 311 00:20:58,849 --> 00:21:03,809 The engines on the DC10 were the General Electric CF6 turbofan engine, 312 00:21:04,209 --> 00:21:07,429 this engine had a very good reputation in aviation 313 00:21:07,429 --> 00:21:11,869 as being safe, reliable, and all around a great engine. 314 00:21:13,809 --> 00:21:16,509 NARRATOR: The CF6 engine seems like a winner, 315 00:21:16,829 --> 00:21:19,609 with innovations in both power and fuel efficiency. 316 00:21:20,289 --> 00:21:24,609 With three of these engines, DC10's can range 3500 miles. 317 00:21:24,609 --> 00:21:27,269 And at a greatly reduced fuel cost. 318 00:21:28,850 --> 00:21:32,330 But could this drive for efficiency come with a downside, 319 00:21:32,810 --> 00:21:34,969 creating a fatal weak point in the plane? 320 00:21:36,610 --> 00:21:39,810 Sometimes, saving money can cost lives... 321 00:21:40,560 --> 00:21:42,230 as a London neighborhood learns. 322 00:21:49,849 --> 00:21:52,149 NARRATOR: A tower block burns through the night... 323 00:21:52,689 --> 00:21:55,809 And horrified residents can only stand by and watch. 324 00:21:56,709 --> 00:21:59,769 How could this happen to a recently renovated apartment building... 325 00:22:08,029 --> 00:22:12,289 Grenfell Tower. London, England. Built in 1974. 326 00:22:13,610 --> 00:22:15,250 While modernizing the building, 327 00:22:15,890 --> 00:22:18,150 aluminum weather-proof sidings are fitted 328 00:22:18,150 --> 00:22:20,290 in place of expensive zinc sidings. 329 00:22:21,070 --> 00:22:24,250 But there is a major problem with this aluminum siding. 330 00:22:25,390 --> 00:22:28,950 This actually had plastic or polyethylene inside of it. 331 00:22:29,009 --> 00:22:31,990 So, the majority of it is combustible, it's flammable. 332 00:22:33,430 --> 00:22:35,230 NARRATOR: There's also a two-inch gap 333 00:22:35,230 --> 00:22:37,610 between the aluminum siding and the insulation. 334 00:22:39,510 --> 00:22:41,850 The perfect funnel to fuel a fire. 335 00:22:42,850 --> 00:22:45,070 It's a really bad design, right? 336 00:22:45,110 --> 00:22:48,950 Because now, what you've done is you've got a little gap, air gap. 337 00:22:49,130 --> 00:22:53,330 So, it's like you've wrapped the entire building in a sheath that's combustible. 338 00:22:53,509 --> 00:22:56,350 And you've given just enough space for air to get in there 339 00:22:56,350 --> 00:22:57,350 and feed the flames. 340 00:22:58,250 --> 00:23:00,730 NARRATOR: In the early hours of Wednesday June 14th, 341 00:23:01,090 --> 00:23:04,110 a refrigerator catches fire on the fourth floor. 342 00:23:05,049 --> 00:23:06,690 Firefighters arrive in ten minutes. 343 00:23:06,870 --> 00:23:08,970 But the blaze spreads too fast. 344 00:23:09,490 --> 00:23:11,630 Once you get this thing started 345 00:23:12,190 --> 00:23:14,990 once the air can get in and fuel it there's no going back. 346 00:23:17,500 --> 00:23:20,680 NARRATOR: The fire takes hold and burns all night long. 347 00:23:27,879 --> 00:23:31,740 As the sun comes up, the scale of the tragedy becomes clear. 348 00:23:35,600 --> 00:23:37,800 It could've easily been avoided. 349 00:23:39,159 --> 00:23:43,260 It emerges that fire-resistant sidings for the whole building 350 00:23:43,260 --> 00:23:46,280 would have only cost another $400,000. 351 00:23:47,240 --> 00:23:52,360 Now for that amount saved 72 lives were lost. 352 00:23:57,300 --> 00:24:01,020 NARRATOR: Coming up... The unthinkable happens to the DC-10... 353 00:24:01,300 --> 00:24:04,419 There is no way that all of the hydraulics 354 00:24:04,419 --> 00:24:08,220 should ever fail all at once, that's impossible. 355 00:24:09,219 --> 00:24:11,560 NARRATOR: And more big things go wrong. 356 00:24:28,630 --> 00:24:30,870 NARRATOR: Planes crash for all kinds of reasons... 357 00:24:31,670 --> 00:24:36,290 Pilot error, mechanical failure, even bad weather. 358 00:24:38,290 --> 00:24:39,290 And like the weather, 359 00:24:39,730 --> 00:24:41,930 there's something else engineers can't control... 360 00:24:48,800 --> 00:24:53,240 NARRATOR: The engineers who designed the futuristic- looking three-engined DC10 361 00:24:53,719 --> 00:24:57,000 are convinced they have preparednfor every possible scenario... 362 00:24:58,159 --> 00:25:00,109 With the most up-to-date safety systems, 363 00:25:00,109 --> 00:25:05,139 including not just one, but two back-ups to its vital hydraulics. 364 00:25:06,339 --> 00:25:08,639 The hydraulics in this type of machine 365 00:25:09,179 --> 00:25:12,960 are essential to assist the pilot and the aircrew 366 00:25:12,960 --> 00:25:14,919 in maneuvering these flight control surfaces 367 00:25:14,919 --> 00:25:19,180 so they don't have to exert, you know, 200, 300 pounds of pressure on the yolk. 368 00:25:19,480 --> 00:25:21,579 NARRATOR: These systems control the plane's movement, 369 00:25:22,159 --> 00:25:25,559 enabling a pilot to change direction, altitude or speed. 370 00:25:26,159 --> 00:25:29,359 If that hydraulic system isn't operating, 371 00:25:29,599 --> 00:25:34,180 it's almost impossible to make the plane go in any direction you want. 372 00:25:35,200 --> 00:25:38,339 There are very few applications of hydraulic systems 373 00:25:38,340 --> 00:25:42,520 that can be more mission-critical than aviation hydraulics. 374 00:25:42,520 --> 00:25:47,120 For the very simple reason that many human lives are at stake. 375 00:25:48,300 --> 00:25:52,120 NARRATOR: Which is why the DC-10 has three hydraulic systems 376 00:25:52,120 --> 00:25:53,980 when it only needs one to fly. 377 00:25:54,500 --> 00:25:56,960 The thought of all three failing at once 378 00:25:57,600 --> 00:26:02,360 was inherently possible but was waved off as not gonna happen. 379 00:26:02,700 --> 00:26:07,379 NARRATOR: For an explosion to take out all three systems is unthinkable. 380 00:26:08,159 --> 00:26:13,339 There's no way that all of the hydraulics should ever fail all at once. 381 00:26:13,740 --> 00:26:14,899 That's impossible. 382 00:26:14,899 --> 00:26:18,500 It was a one in a billion catastrophic failure, 383 00:26:19,060 --> 00:26:21,760 the likes of which no one had ever seen before. 384 00:26:21,980 --> 00:26:25,740 NARRATOR: But that billion to one bad luck chance does happen... 385 00:26:26,100 --> 00:26:30,899 As the pilot and passengers of one of the most famous aircraft of all time 386 00:26:30,899 --> 00:26:32,800 find out in the skies near Paris. 387 00:26:37,530 --> 00:26:42,409 NARRATOR: July 2000. 109 passengers board an Air France Concorde 388 00:26:42,409 --> 00:26:44,169 for a luxurious flight to New York. 389 00:26:44,750 --> 00:26:48,289 After an hour's delay, it finally gets clearance to take off. 390 00:26:48,629 --> 00:26:50,629 MATT: The winds had changed at that point, 391 00:26:50,710 --> 00:26:52,990 and instead of taxi-ing to another runway 392 00:26:52,990 --> 00:26:56,570 and creating a further delay the aircrew elected 393 00:26:56,570 --> 00:26:59,090 to go ahead and take-off on the first runway. 394 00:26:59,810 --> 00:27:02,389 NARRATOR: But this runway hasn't been inspected. 395 00:27:03,270 --> 00:27:07,370 ROB: Just five minutes earlier a DC-10 had taken off from the same runway. 396 00:27:07,590 --> 00:27:11,350 And as it did so, it lost a titanium alloy strip. 397 00:27:12,269 --> 00:27:15,609 A small piece of titanium, the size of a ruler, not that big. 398 00:27:16,710 --> 00:27:20,690 That day they'd failed to do a foreign object and debris, or a FOD check 399 00:27:20,690 --> 00:27:22,770 on the runway prior to their departure. 400 00:27:23,250 --> 00:27:25,349 So, the piece of metal went undetected. 401 00:27:28,259 --> 00:27:30,300 NARRATOR: As the Concorde begins take-off, 402 00:27:30,960 --> 00:27:34,000 the pilots are unaware of the 16-inch metal strip 403 00:27:34,000 --> 00:27:35,540 lying directly in their path. 404 00:27:37,080 --> 00:27:40,040 And the plane's tires run right over it. 405 00:27:41,060 --> 00:27:45,820 The Concorde going down the runway and hitting that piece, 406 00:27:46,160 --> 00:27:50,820 that strip of metal from a DC 10 is a one in a million chance. 407 00:27:51,240 --> 00:27:54,680 I mean if that had been off to the left just a little bit 408 00:27:54,800 --> 00:27:56,200 they would have completely missed it. 409 00:27:56,520 --> 00:27:59,900 The rubber explodes. Portions of the tire debris 410 00:28:00,300 --> 00:28:01,580 slam into the fuel tank. 411 00:28:02,420 --> 00:28:04,480 NARRATOR: It breaks a seal on the tank. 412 00:28:05,060 --> 00:28:10,040 You never want jet fuel to be leaking out of a plane that's about to take off. 413 00:28:10,380 --> 00:28:14,100 NARRATOR: There's a spark in the damaged fuel cell, and it ignites. 414 00:28:16,450 --> 00:28:21,350 As the plane takes off, this engine fire becomes catastrophically destructive, 415 00:28:21,350 --> 00:28:22,610 and the plane crashes. 416 00:28:26,200 --> 00:28:29,620 NARRATOR: All 109 people on board die in the crash. 417 00:28:31,080 --> 00:28:36,140 Bad luck brought down one of the most advanced passenger jets of all time. 418 00:28:37,600 --> 00:28:41,420 NARRATOR: Coming up... The crew battle to save flight 232 419 00:28:44,319 --> 00:28:47,100 They've got one shot to get it down. 420 00:29:03,209 --> 00:29:07,070 NARRATOR: United Airlines 232 is at 37,000ft 421 00:29:07,070 --> 00:29:08,070 on its way to Chicago. 422 00:29:09,250 --> 00:29:14,269 On today's flight, 296 people including Jerry Schemmel. 423 00:29:15,630 --> 00:29:18,510 We're Just cruising along, it's a smooth flight, 424 00:29:18,670 --> 00:29:20,910 and I'm starting to get a little sleepy, 425 00:29:21,009 --> 00:29:22,670 I'm thinking a little nap might be good. 426 00:29:23,089 --> 00:29:24,829 Didn't really think anything was out of the ordinary. 427 00:29:29,500 --> 00:29:33,319 NARRATOR: A half an inch crack in the fan disk of the DC10's tail engine 428 00:29:33,320 --> 00:29:35,800 has gone unnoticed for 17 years. 429 00:29:36,939 --> 00:29:39,300 But it's about to reach breaking point... 430 00:29:40,180 --> 00:29:41,579 I hear this explosion. 431 00:29:46,500 --> 00:29:48,519 The pilots don't know what is going on 432 00:29:48,700 --> 00:29:50,779 but something is very, very wrong with the aircraft. 433 00:29:51,319 --> 00:29:55,220 NARRATOR: They quickly realize the explosion has taken out the tail engine 434 00:29:55,460 --> 00:29:57,039 It came from the back of the plane, 435 00:29:57,420 --> 00:29:59,020 you could hear the explosion, you could feel it, 436 00:29:59,179 --> 00:30:01,220 and you could feel the plane beginning to drop after that. 437 00:30:01,599 --> 00:30:04,319 And I thought, wow this is really serious. 438 00:30:04,760 --> 00:30:06,340 NARRATOR: Even if one engine fails, 439 00:30:06,740 --> 00:30:09,500 the DC-10 should be able to fly with the other two. 440 00:30:09,859 --> 00:30:12,140 But this plane isn't responding. 441 00:30:12,559 --> 00:30:16,299 The pilots are unable to steer the plane go up and down 442 00:30:16,299 --> 00:30:17,880 they are basically powerless. 443 00:30:19,259 --> 00:30:21,079 NARRATOR: Exploding shrapnel from the tail engine 444 00:30:21,080 --> 00:30:23,740 has cut through all three hydraulic systems. 445 00:30:26,200 --> 00:30:30,060 The odds that all three hydraulic systems were to fail at once 446 00:30:30,060 --> 00:30:33,340 was so rare that it wasn't even in the emergency procedures. 447 00:30:34,100 --> 00:30:39,200 Without these controls the pilots can't steer the plane or take it up or down. 448 00:30:39,620 --> 00:30:43,039 NARRATOR: The plane is descending six times faster than it should be. 449 00:30:44,279 --> 00:30:46,759 I grabbed my arm rests and held on. 450 00:30:47,039 --> 00:30:48,980 NARRATOR: In the cockpit, alarms are blaring. 451 00:30:49,240 --> 00:30:51,860 The plane is now almost impossible to control. 452 00:30:52,059 --> 00:30:53,720 The first thing that was going through their heads was, 453 00:30:55,380 --> 00:30:57,100 what the hell happened, what's going on back there? 454 00:30:59,771 --> 00:31:04,172 (CLOCK TICKING) 455 00:31:04,299 --> 00:31:07,519 NARRATOR: The flight crew radio Minneapolis Air Traffic Control 456 00:31:07,519 --> 00:31:08,960 for emergency assistance. 457 00:31:18,299 --> 00:31:20,399 NARRATOR: They're directed to the nearest airport, 458 00:31:21,099 --> 00:31:22,099 Sioux City, Iowa. 459 00:31:30,840 --> 00:31:32,860 NARRATOR: As the plane descends, 460 00:31:32,860 --> 00:31:35,040 it constantly rolls to the right, 461 00:31:35,460 --> 00:31:37,000 threatening to turn upside-down. 462 00:31:37,879 --> 00:31:40,680 If that happens and flips all the way over 463 00:31:41,379 --> 00:31:43,599 the plane will tumble to its doom. 464 00:31:44,854 --> 00:31:49,163 (CLOCK TICKING) 465 00:31:49,299 --> 00:31:52,240 NARRATOR: Pilot captain Al Haynes fights to level the plane. 466 00:31:53,320 --> 00:31:56,740 The one thing that they do have control over is the throttles 467 00:31:56,860 --> 00:32:00,560 which provides power to each of the engines under the wings. 468 00:32:00,680 --> 00:32:04,640 So, the captain pulls back on the throttle on one side 469 00:32:04,640 --> 00:32:06,960 and ups the power on the other side 470 00:32:07,080 --> 00:32:10,300 and this slowly brings the wings back into alignment. 471 00:32:11,440 --> 00:32:15,220 It works and the captain regains a crude form of steering 472 00:32:15,220 --> 00:32:18,620 using just the throttles, but there's another problem, 473 00:32:19,019 --> 00:32:22,960 the captain now finds he can only make right hand turns. 474 00:32:34,740 --> 00:32:36,860 NARRATOR: DC 10 training instructor Denny Fitch 475 00:32:36,860 --> 00:32:38,300 is sitting in first class. 476 00:32:39,100 --> 00:32:42,860 By coincidence, he's practiced this exact scenario 477 00:32:42,860 --> 00:32:43,940 on a flight simulator, 478 00:32:43,940 --> 00:32:46,820 after hearing about a similar failure in Japan. 479 00:32:47,300 --> 00:32:50,759 He races to the cockpit to help and takes over the throttles, 480 00:32:50,759 --> 00:32:53,000 as the pilots figure out their next move. 481 00:32:55,150 --> 00:32:58,990 NARRATOR: The DC10 begins a succession of circles over Iowa... 482 00:32:59,610 --> 00:33:03,310 With every turn to the right it drops 1500-feet. 483 00:33:04,450 --> 00:33:08,470 I could feel this plane taking this right turn, 484 00:33:08,610 --> 00:33:10,610 and we just kept going that way. And I thought 485 00:33:10,730 --> 00:33:12,310 why are we just continuing to turn right, 486 00:33:12,370 --> 00:33:13,670 why aren't we ever levelling off. 487 00:33:14,665 --> 00:33:18,519 (CLOCK TICKING) 488 00:33:18,649 --> 00:33:21,090 Captain Haynes got on the PA system and told us 489 00:33:21,090 --> 00:33:24,770 that we'd been given a directive to make an emergency landing at Sioux City, Iowa. 490 00:33:25,089 --> 00:33:27,009 He said I want everybody in their seats, 491 00:33:27,250 --> 00:33:29,509 the seatbelts are fastened, they're pulled tight 492 00:33:30,230 --> 00:33:32,509 because, he said, we are in serious trouble. 493 00:33:33,809 --> 00:33:36,289 NARRATOR: Emergency vehicles scramble for a crash landing. 494 00:33:39,009 --> 00:33:42,509 I think we circled around four or five times trying to get to Sioux City. 495 00:33:42,640 --> 00:33:46,768 (CLOCK TICKING) 496 00:33:46,900 --> 00:33:52,420 NARRATOR: At 3.53pm, the crew put the DC-10 into its final turn. 497 00:33:52,780 --> 00:33:54,300 It's the moment of truth. 498 00:33:56,000 --> 00:33:57,980 JERRY: Captain Haynes is on the PA system 499 00:33:57,980 --> 00:34:02,000 telling us that he was gonna give us a command to brace three seconds before we hit. 500 00:34:02,720 --> 00:34:03,720 He said... 501 00:34:04,040 --> 00:34:09,620 He said I want everybody to understand this is going to be rough. 502 00:34:09,908 --> 00:34:16,908 (CLOCK TICKING) 503 00:34:19,480 --> 00:34:22,018 I thought to myself let's just get this thing over with 504 00:34:22,099 --> 00:34:25,179 because I'm as ready as I can be mentally and physically. 505 00:34:25,400 --> 00:34:29,079 I've said my prayers, I've said my goodbyes in my own mind. 506 00:34:30,799 --> 00:34:35,179 NARRATOR: A normal DC10 landing speed is 120mph 507 00:34:35,460 --> 00:34:38,319 but this plane is approaching twice as fast. 508 00:34:41,570 --> 00:34:45,110 And they're almost going to make the runway when all of a sudden... 509 00:34:45,252 --> 00:34:52,252 (CLOCK TICKING) 510 00:34:54,300 --> 00:34:56,340 The wing tips and catches. 511 00:34:56,760 --> 00:34:59,320 And the plane just breaks apart and tumbles. 512 00:35:07,050 --> 00:35:10,070 I'm looking around, I'm seeing bodies being thrown about. 513 00:35:10,250 --> 00:35:12,750 Some were out of their chairs, some were still strapped in their chairs, 514 00:35:13,190 --> 00:35:16,230 we bounced a couple of times, we start sliding and going forward. 515 00:35:16,489 --> 00:35:18,969 The nose of the plane dug into the runway 516 00:35:19,170 --> 00:35:21,150 and we flipped over end to end. 517 00:35:21,470 --> 00:35:25,670 The plane broke into big pieces at that point and I just held on... 518 00:35:26,290 --> 00:35:29,650 and slid upside down and backwards and finally came to a halt. 519 00:35:36,550 --> 00:35:38,710 JERRY: I was getting ready to run away from the aircraft, 520 00:35:38,990 --> 00:35:41,090 I heard a baby crying back inside the wreckage 521 00:35:41,230 --> 00:35:42,430 and I followed the cries. 522 00:35:42,890 --> 00:35:45,310 And by this time we were almost completely full of smoke. 523 00:35:45,350 --> 00:35:47,550 I couldn't see anything but I could hear the cries. 524 00:35:47,730 --> 00:35:48,730 So I honed in on it 525 00:35:48,770 --> 00:35:52,670 and I realized the crying was coming from inside an overhead bin in this plane. 526 00:35:52,810 --> 00:35:55,050 I find the latch, open the latch, lift the lid 527 00:35:55,310 --> 00:35:57,230 and just sort of scooped the baby with one arm 528 00:35:57,269 --> 00:35:59,110 and as soon as I grabbed her she stopped crying. 529 00:35:59,610 --> 00:36:02,890 And then I just turned around headed for the opening and got outside the plane. 530 00:36:03,570 --> 00:36:08,110 NARRATOR: Emergency crews swarm over the wreckage. 112 die. 531 00:36:08,530 --> 00:36:13,289 They find the three flight-crewand Denny unconscious, but alive. 532 00:36:14,570 --> 00:36:18,090 Miraculously 184 passengers and crew survived the impact. 533 00:36:18,970 --> 00:36:23,310 I looked back and I could see the wreckage from where I'd come out of. 534 00:36:23,730 --> 00:36:27,130 And it was at that point that it hit me how bad this was, 535 00:36:27,650 --> 00:36:29,590 because I knew we were in a big plane. 536 00:36:30,110 --> 00:36:32,570 I'm thinking, this is a terrible disaster. 537 00:36:33,050 --> 00:36:35,130 NARRATOR: The footage shocks the nation. 538 00:36:35,610 --> 00:36:38,830 And with some 400 DC-10's still flying 539 00:36:39,250 --> 00:36:42,750 the aviation industry is desperate to figure out what went wrong. 540 00:36:43,090 --> 00:36:46,350 But Investigators face a monumental task. 541 00:36:47,150 --> 00:36:52,030 Debris is spread across -Iowa. And a vital piece of the puzzle is missing. 542 00:37:21,400 --> 00:37:23,220 NARRATOR: When big things go wrong, 543 00:37:23,620 --> 00:37:25,100 the causes can be obvious. 544 00:37:37,199 --> 00:37:40,519 NARRATOR: But other times engineers have to search for answers. 545 00:37:40,673 --> 00:37:45,004 ARCHIVE: You can really see what is missing 546 00:37:45,160 --> 00:37:47,879 that whole fan area is missing. 547 00:37:48,439 --> 00:37:50,060 NARRATOR: One vital piece of evidence 548 00:37:50,060 --> 00:37:52,540 in the fatal Sioux City crash is missing. 549 00:37:52,879 --> 00:37:55,259 The fan disc is not at the debris site 550 00:37:55,259 --> 00:37:57,099 and could be anywhere in Iowa. 551 00:37:57,559 --> 00:38:00,859 ARCHIVE: The obstacle is 20 square miles of farmland. 552 00:38:01,059 --> 00:38:04,159 The key part still missing used to be in this empty casing. 553 00:38:04,159 --> 00:38:08,439 The shell that held engine number 2 and the fan that pushed air to it. 554 00:38:08,779 --> 00:38:14,359 NARRATOR: Months go by and despite a $50,000 reward the fan disk remains lost. 555 00:38:15,099 --> 00:38:17,460 They searched high and low for this fan disk. 556 00:38:17,679 --> 00:38:21,500 the search was extensive, farm land over the mid-west, 557 00:38:21,500 --> 00:38:25,559 and further, hidden by corn and crops. 558 00:38:25,759 --> 00:38:29,960 It didn't turn up until later when a farmer was harvesting 559 00:38:29,960 --> 00:38:33,219 and they literally ran into a fan disk. 560 00:38:34,020 --> 00:38:37,040 NARRATOR: Now investigators have the final piece to learn 561 00:38:37,040 --> 00:38:40,720 what caused United Airlines Flight 232 to crash. 562 00:38:41,519 --> 00:38:43,759 And seen through the eyes of an engineer, 563 00:38:44,379 --> 00:38:45,619 the clues are clear... 564 00:38:46,919 --> 00:38:48,119 Cutting costs... 565 00:38:49,079 --> 00:38:53,859 The third engine on the tail section is a disaster waiting to happen. 566 00:38:54,559 --> 00:38:55,559 NARRATOR: A hidden flaw... 567 00:38:56,179 --> 00:38:58,019 We call it a fatigue crack. 568 00:38:58,919 --> 00:39:00,139 NARRATOR: Missed signs... 569 00:39:01,899 --> 00:39:05,279 Maintenance teams failed to pick up this crack time and time again. 570 00:39:05,799 --> 00:39:07,460 NARRATOR: And sheer bad luck... 571 00:39:07,659 --> 00:39:12,179 The thought of all three failing at once was waved off as not gonna happen. 572 00:39:20,849 --> 00:39:23,309 NARRATOR: As a result of the Sioux City crash, 573 00:39:24,230 --> 00:39:27,190 investigators would make 31 sweeping recommendations 574 00:39:27,190 --> 00:39:29,929 to improve inspections and airline safety. 575 00:39:30,710 --> 00:39:34,410 MATT: Several of them revolving around redundancy and hydraulic systems, 576 00:39:34,410 --> 00:39:35,930 the protection of these hydraulic systems 577 00:39:36,110 --> 00:39:42,310 and then refined manufacturing and inspection processes for these fan disks. 578 00:39:43,009 --> 00:39:47,309 NARRATOR: But why, in 1989, faced with such a catastrophic failure 579 00:39:47,309 --> 00:39:52,610 of its hydraulic systems, didn't United 232 simply fall from the skies? 580 00:39:53,150 --> 00:39:57,529 You have a huge piece of metal that is largely uncontrolled. 581 00:39:57,869 --> 00:40:00,989 How do you bring that down and land it with only the engines? 582 00:40:01,790 --> 00:40:03,710 NARRATOR: The answer lies in the quick thinking 583 00:40:03,710 --> 00:40:04,710 of the pilots, 584 00:40:04,929 --> 00:40:06,630 Denny Fitch and the crew. 585 00:40:08,929 --> 00:40:12,370 It was apparent to us that we had lost all of our hydraulic fluid 586 00:40:13,290 --> 00:40:15,690 and when I asked Dudley for the procedure for that... 587 00:40:16,290 --> 00:40:17,410 he said there isn't one. 588 00:40:18,190 --> 00:40:20,210 So we made it up as we went along. 589 00:40:20,650 --> 00:40:23,230 I've heard pilots, many of them over the years, 590 00:40:23,329 --> 00:40:26,750 that went into a simulator, put in to a DC-10, 591 00:40:26,929 --> 00:40:29,849 same conditions we had, number 2 engine explodes, 592 00:40:30,270 --> 00:40:33,450 hydraulics go out, and they say every single time 593 00:40:33,549 --> 00:40:36,670 that plane nose dives to ground and the computer said everybody's dead. 594 00:40:37,230 --> 00:40:40,690 We have a lot of experience here and it showed up in the cockpit. 595 00:40:41,309 --> 00:40:46,130 There is no substitute as far as I am concerned in experience 596 00:40:46,469 --> 00:40:49,210 and we had it and it shows that experience is very important... 597 00:40:50,389 --> 00:40:54,150 NARRATOR: The heroic actions of the pilots on flight 232 598 00:40:54,150 --> 00:40:57,309 undoubtedly saved Jerry and the other survivors. 599 00:40:58,170 --> 00:41:01,730 Proving when big things go wrong, people can step in. 600 00:41:03,710 --> 00:41:07,230 Accidents will happen. Planes will go wrong. 601 00:41:08,029 --> 00:41:11,750 And when they do it is the actions of one or two people 602 00:41:11,750 --> 00:41:13,089 that can save hundreds. 603 00:41:15,230 --> 00:41:18,269 When I look at it today, 31 plus years later, 604 00:41:18,330 --> 00:41:21,950 I think we could not have had a better crew inside that cockpit 605 00:41:21,950 --> 00:41:24,690 to give us a shot at making this thing work 606 00:41:24,690 --> 00:41:26,150 and not everybody dying. 607 00:41:27,069 --> 00:41:31,109 We overcame the odds because we had a group of four people in that cockpit 608 00:41:31,109 --> 00:41:33,510 that did all they could, to try to save lives. 609 00:41:34,289 --> 00:41:37,309 I don't know if it could have gone any better than it did. 610 00:41:38,169 --> 00:41:41,250 I thank them personally, and I still do in my mind every day 611 00:41:41,250 --> 00:41:43,710 for their heroic efforts inside that cockpit.