a mysterious flaw brings down a boeing 737. >> all of a sudden i heard a big explosion. >> there's something going on that left no marks. no calling card. >> shortly after takeoff, a powerful explosion rips apart twa flight 800, igniting controversy about what really happened. >> if anybody thinks that this is involved in any coverup, they are wrong. >> conflicting commands put two jelt jets on a collision course.

the devastation provoked a violent act. >> it was a crime of almost unimaginable magnitude. >> terrifying crashes and the gripping investigations. >> the navy is a suspect. >> dramatic animations take you inside catastrophic crashes and what caused them. ♪ september 8, 1994. electricaling fr i traveling from chicago, u.s. air flight 427 is flying as it prepares to land in pittsburgh. when suddenly, the boeing 737 spirals out of control.

28 seconds later, it smashes down into a field in hopewell township, pennsylvania. >> it was a real loud motor that was screaming. all of a sudden i heard a big explosion. >> police officer george david is 2 1/2 miles away from the crash site which happens to be next to his farm. >> that was when i got the phone call. they said, you better get up here right now. a plane had just crashed on the property. >> when david arrives, it's a horrifying scene. the airport has been obliterated by the 300 mile per hour impact. there is no hope for the 132 passengers and crew on board. >> i've been a policeman for 25 years. i've seen a lot of things. that was the worst that i've ever seen it. >> investigators will try to find clues among the

destruction. it's a daunting task for the ntsb investigator in charge, tom howiter. >> it was the first time u.s. ntsb team had to wear biohazard suits to go on site. because of the impact and the level of destruction, there were human remains everywhere. >> a lot of them are burned. they're dieing from the fuel. >> an aviation maintenance technician captures the scene up close providing a rare and vivid glimpse into the investigation. >> there was no airplane left. clearly the airplane hit close to being vertical at a high rate of speed. >> looks like the right wing. you can see it's not very far from the tail section. cockpit crashed right up over the hill there.

the left wing you see up on top of the hill. in fact, down here is the right wing. what's left of it. >> the pilot who has extensive background with 737s is assigned to the investigation as a representative for the airline pilots association. >> i'm standing right about in line with where the airplane was facing. i'm facing the direction the airplane was. it's directly behind. as an aircraft accident investigator, you have to shift into this, i can't help the people that are here. i now need to understand what happened so that we don't have a recurrence. >> several teams work to identify and recover pieces of the wreckage. >> left end. >> this is part of the trash that we have separated out. clothes, some wires.

stuff here is going in for decontamination. before it goes to the hangar. >> the wreckage will be sorted and analyzed piece by piece. >> this is day one of the sorting. >> the flight data and cockpit voice recorders were ejected from the airport on impact and are quickly recovered. they don't provide any clear answers. there are no sounds of explosions and no evidence of a major mechanical failure. the recorders do provide investigators with a clearer picture of the flight crew's final moments. one minute before impact, the crew of flight 427 is alerted to another airplane that will be passing below them. >> they are looking for the airplane the first officer acquires it visually and tells the captain, yes, i see the jet.

and then they encounter the weight turbulence of a delta airlines 727. it's not an uncommon event at all. the airplane rocks around and moves. from that moment of encountering the wake, something happened. they couldn't stop the roll in the airplane. just was very difficult to listen to as a pilot because i could hear them struggling for control of the airplane and every second that ticked by they were losing that battle. and they never quit. they never quit trying to fly the airplane. >> as seen in this video, investigators set up a test flight to examine the possibility that the u.s. air p pilots were startled by a wake causing them to lose control. >> we found was that you could take the airplane, let go of the controls and the airplane would come out of the wake and regain its composure and fly on with no problems. there was no reason to lose

control of the airplane. >> one of the lead investigators made a very, very good observation. that was that if the wake of the 727 could cause the loss of control of a 737, we would have 737s falling out of the sky weekly or more. >> investigators zero in on flight 427's rotation or yawing toward the left just moments before the pilots lost control. >> we knew the airplane yawed. the question was, what would cause that? it quickly became apparent that the only device that could make the airplane yaw the way it did is the rudder. that's what it was designed for. >> the rudder is positioned at the tail of the boeing 737 and is used by pilots to control the plane's movement to the left and right. trying to determine how the rudder could have malfunctioned, investigators test every theory they have. >> there were a couple of people

on the airplane that were very heavy. someone said, well, what would happen if the floor gave way and a passenger stepped on a control cable? could that have done it? >> we did a test. that quickly became obvious that that event couldn't happen. the amount of weight required was too great. we looked at all kinds of potential failures. everything was considered. one by one we eliminated them. >> we felt confident there was a rudder issue. but we didn't know what it was. there's something going on back in the tail of the airplane. we don't understand. i described it as a gremlin that left no mark, left no calling card. >> it's not the only unsolved accident weighing on investigators. three years earlier, an amateur photographer captures the burning wreckage of united flight 585 in colorado springs. the crash kills all 25 people on board.

sg >> the safety board could not determine exactly what caused the accident. people started linking u.s. 427 to united 525. both were on approach. both airplanes suddenly rolled and dove into the ground for no reason. >> the two flights have something else in common. both airplanes are boeing 737s. >> the most widely used jet in the world. the second time something unexpected had happened and resulted in the loss of an airplane. if another one went down, they were going to ground the airplane. the ramifications forgrounding the 737 was severe. it sets off a global economic catastrophe. we had to find out what happened. >> coming up, another boeing 737 ends up in serious trouble. could that crisis lead to a break in the case? >> so you have two pilots shoveling with all their might on a rudder pedal. all it's doing is driving back.

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u.s. air flight 427 smashes down outside of pittsburgh. it's the second boeing 737 in three years to suddenly roll for unknown reasons and then crash, killing everyone on board. it's a mystery threatening to ground the most widely used jet in the world. investigators suspect a problem with the rudder, which controls the plane's movement to the left and right. but they find no evidence of a malfunction. nearly two years after the crash, a possible break in the case. the pilot of an eastwind airlines boeing 737 experiences a sudden roll as the jet approaches richmond, virginia.

>> he quickly got on the rudder pedals. so you had two pilots shoveling with all their might on a rudder pedal. all it's doing is driving them back. it keeps pushing back at them. it doesn't go forward. we never had this report from a crew before of a pedal back forcing against them. now we're into a different scenario. >> fortunately, they were at a higher air speed than 427, which gave them more roll control. they were able to successfully land the airplane. >> after hearing the pilots' experience with the rudder pedals, investigators suspect a jam may be the problem in the airplane's rudder system. >> the pilots control the rudder on the 737 with pedals. those ped aals are connected vi cables to the muscle, if you will, that physically moves the rudder. the power control unit. like power steering in your car, it's hydraulically powered. >> about the size of a soda can,

the power control unit or pcu houses a set of valves called the duo serve-o valve. it directed hydraulic fluid to move the rudder. >> it's the valve from a power control unit. the pilot inputs go into the arms and by moving back and forth across the openings, it would redirect the fluid. >> in the days after the u.s. air accident, investigators recovered flight 427's pcu from the crash site. if something did malfunction inside this pcu, it left no evidence. >> the valves were not badly scarred. there were no marks. there wasn't an instant indication of what would have caused the power control unit to have problems. >> investigators run a battery of tests on the pcus from u.s. air 427 and eastwind airlines trying to determine if the units

can jam. what they find is even more alarming. not only can the pcu jam, but it can then deflect the rudder in the opposite direction. >> if you jam the secondary valve just slightly off neutral, you could cause the valves to basically misalign and pour hydraulic fluid in the wrong direction so the rudder reversed opposition. it's like driving the car to the left and it goes to the right. you will never figure this out before you go off the road. >> they found a lethal malfunction in the size of a valve the size of of a pencil capable of bringing down a 737. the malfunction leaves no marks or scars. almost as if it never happened. matching exactly what investigators found in u.s. air 427. >> all of a sudden, you put the reversal scenario in and it started coming together that all these parts now fit. the big puzzle we have had the edges and everything else.

now the centerpieces are locking in. >> when flight 427's crew encounters the turbulence of a passing airplane, they press down on the rudder pedals to counter the wake and move the airplane to the right. the dual valve inside the power control unit jams. and misaligns. causing the rudder to be deflected in the opposite direction. >> what they didn't recognize was that the rudder was full over. so as they are pushing, the rudder is not moving. because it's jammed. they don't know this. >> then the nose starts to fall through and the crew pulls back to bring the nose up. the airport enters what looks like a spin into the ground. the pilots of 427 faced a condition they had never heard of, they weren't trained for. from a pilot's standpoint, you never consider the possibility that if you turn to the right, the airplane is going to go to the left. they didn't have a long time to

sort it out. they had around the 13 seconds to diagnose the problem, deal with it effectively. >> it takes 4 1/2 years, one of the longest accident investigations in aviation history, to solve the mystery of u.s. air flight 427. with it, investigators are able to bring closure to another cold case. united flight 585. the other boeing 737 that crashed three years earlier. >> the rudder system on the 737 fleet has been completely resigned. it's a very different system now than it was at that time. there's a lot of changes also to flight crew training, more hands-on flying, being ready to recover from unusual upsets and unusual events. history has proven us to be right. there has not been another occurrence of the rudder hard over since -- i think we made a good airplane even better. >> coming up, one of the most infamous aviation disasters in

history. >> you saw what appeared to be a flare going straight up. >> what really happened to twa flight 800. >> microscopic explosive traces of unknown origin have been found. where tarzan go! tarzan does not know where tarzan go. hey, excuse me, do you know where the waterfall is? waterfall? no, me tarzan, king of jungle. why don't you want to just ask somebody? if you're a couple, you fight over directions. it's what you do. if you want to save fifteen percent or more on car insurance, you switch to geico. oh ohhhhh it's what you do. ohhhhhh! do you have to do that right in my ear? you switch to geico.

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july 17, 1996. beachgoers and boaters are enjoying a summer evening on long island, new york. nearby, at jfk airplane, a boeing 747 is taking off, carrying 230 passengers and crew headed for paris. less than a minute later, as twa flight 800 is climbing over the atlantic, there's an explosion. the force rips the airplane apart. other pilots in the area begin reporting what they have seen to air traffic control. >> saw an explosion. about 16,000 feet or something like that, it just went down. in the water.

>> rescue teams scour the area for survivors. but no one is found alive. as dusk turns to dark, all that can be seen of the boeing 747 is the burping debris and jet fuel on the surface of the water. >> we see the big flames. we didn't expect to see that. when we see that, we knew it was going to be pretty bad. we found our first victim. there was a female. in bad shape. >> as the wreckage burns, so does speculation that there may have been a bomb on board the plane. >> you have to remember the time, the first attempt at the world trade center. and i think terrorism was just getting on people's radar. >> by morning, eyewitness accounts point to yet another alarming possibility. a missile. >> we saw what appeared to be a flare going straight up.

then we see this white thing and then a big ball of fire come out of it and two pieces on fire fell into the water. >> the ntsb sends a team to determine what brought down the plane. white t while the fbi launches a criminal investigation. >> if it's a tear othrrorist eve have the challenge to find out who the cowards were who did this. >> is it possible the aviation safety issue? we need to know about. so there became two investigati investigations. one for the fbi and one for the ntsb. >> the first challenge for investigators, recovering the victim s and the wreckage submerges in the ocean. investigators employ the resources of the u.s. navy. it will be one of the largest diver assisted salvage operations ever conducted. it's both difficult and

dangerous. >> i talked to the master diver. he was talking about that it was like diving in razor blades. >> as pieces of the wreckage are recovered and examined, investigators find what could be a frightening break in the case. >> microscopic explosive traces of unknown origin have been found. >> even more disturbing, rumors are swirling online that a missile may not have been fired by terrorists but by the u.s. military. the fbi investigates the claims, scrutinizing u.s. naval vessels in the area at the time of the crash. but they find no evidence. >> i can assure you we looked at every angle, every possibility and the military of this country has had nothing to do with this horrendous tragedy. >> proponents of a friendly fire theory believe there's been a

coverup. >> the navy is a suspect. the navy is a suspect. why should they be involved in the investigation? >> if anybody thinks that this chairman, this agency is involved in any kind of coverup, then they are wrong. >> i tried to deal with the distractions. our investigators could deal with doing their work. >> investigators have been recovering as much of twa flight 800 as they can. pulling pieces from the bottom of the ocean and transferring them to a hangar where they will attempt to reconstruct the aircraft. >> to see that mass of jumble and wires brought home to me how difficult it's going to be to try to put that all back together again. >> investigators recover hundreds of pieces of the wreckage. an astounding 95% of the airplane. when they finish assembling this massive puzzle, it's the largest aircraft reconstruction in history. >> when an explosive device goes

off in close proximity to medal, it leaves behind small craters and localized melting and soot patterns and things like that. we were able to determine that there was absolutely no evidence of a bomb exploding close to the structure and there was no evidence that any kind of particle might have penetrated from a missile that exploded nearby. >> looking inside the airplane, we have human remains looking for particles of an explosion captured by the dobody. seat cushions, other parts we had examined looking for evidence of an explosion. we didn't see that in any of the evidence we saw coming back. >> as for the traces of explosive residue found, investigators believe it could have been transferred from military ships that transported the wreckage from the crash site. after 16 months, the fbi closes their parallel investigation. >> the team conducted a total and thorough investigation.

there was no evidence of high explosive damage. two, there was no evidence of an explosion of a missile warhead. three, there was no evidence of missile impact. >> if it isn't a criminal act, then what brought down twa flight 800? and how can the eyewitness accounts be explained? >> coming up -- >> we were surprised. it didn't take a lot of energy to ignite these vapors. [burke] hot dog.seen it.covered it. we know a thing or two because we've seen a thing or two. ♪ we are farmers. bum-pa-dum, bum-bum-bum-bum ♪ my school reunion's comi♪ fast. could be bad. could be a blast. can't find a single thing to wear. will they be looking at my hair? won't be the same without you bro. ♪ when it's go, go to choicehotels.com.

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the hour's top stories. canadian officials are working to get a handle on the country's largest wildfire they say is unpredictable and dangerous. it forced nearly 88,000 to flee. firefighters estimate more than 1,600 homes and buildings have been destroyed. donald trump is walking back his tax plan. now saying he is open to raising taxes on the wealthy if he is

elected president. this ahead of the general election battle. now back to "why planes crash." july 17, 1996. twa flight 800 explodes in flames shortly after takeoff. the fbi rules out a bomb or missile. but it will take a four-year investigation, the most costly and extensive in the ntsb's history to determine the cause. after pulling debris from the ocean, investigators conclude the airplane broke apart into three sections. >> the front section of the airplane containing the cockpit and the first class area broke off. that just fell to the ground. and then much further away, you had the rest of the airplane which seems odd. that piece had to continue some part of flight for a lot longer.

we went back and started looking at the pieces that came off first. they came out of areas around the wing center fuel tank. so it started becoming apparent that whatever happened happened inside the wing center fuel tank. >> unlike gasoline, jet fuel isn't highly flammable. but as this faa test shows, when it's heated, the vapors that are produced can be explosive. as twa flight 800 prepares to take off from new york's jfk airport, the center wing fuel tank, about the size of a two-car garage, is nearly empty. >> all that was in that fuel tank was basically just residual fuel. just a small amount of fuel sloshing around in the bottom of the tank. >> given the short duration of this particular flight, the operators don't usually use or put fuel into the center fuel tank because they don't need it. the wings hold a sufficient amount of fuel. >> if you can save money and get

better performance by leaving the fuel out of it. >> with passengers waiting on board flight 800, a delay with baggage is keeping the plane at the gate. >> it was a hot day in new york. they have had the air conditioning packs running to keep the aircraft cool. the air conditioning packs are mounted in close proximity to the center fuel tank. >> as the ac packs work to keep the airplane cool, they are actually generating heat underneath the center wing fuel tank. >> the fuel tank was actually getting very warm. so when the airplane takes off, you have this warm fuel vapor. if there was a full load of fuel in the tank, it could absorb the heat with no problem. >> it was believed that the fuel tanks were not really flammable. they couldn't really even be ignited because the temperature wasn't great enough. >> so we took a 747 tested it with very similar conditions. we were all surprised how hot it

got and also it didn't take a lot of energy to ignite these vapors. it's len thss than if you rub y feet across the carpet and touch a doorknob. less energy than that was needed to ignite the fuel tank. >> there's no clear source of ignition on board twa flight 800. by design, only low voltage wires are used inside the fuel tank. >> however, those low voltage wires pass in very close proximity to much higher voltage wires in wiring bundles. and as the airplane's age and the wiring bundles chafe, you can have occasions where there's arcing or shorting between the wires which introduces high voltage into low voltage wire and now you have an ignition source. >> we don't have a piece of wire or something that can hold up

and say, this absolutely did it. there's not enough left. the ntsb believes and i believe it was most likely a short-circuit of the wiring. that certainly was very possible. you look at all the evidence and whatever ignited the fuel in the tank was inside the tank. it didn't come from the outside. >> the cockpit voice recorder recovered one week after the crash may provide evidence. the pilot is heard observing a strange reading in a fuel flow gauge. >> that's probably the indication of some type of short-circuit going on. this airplane was old. it was getting ready to be taken out of service. >> there are more clues. one second before the cockpit voice recording ends, there are two dropouts in background noise suggesting a possible arc on the cockpit wiring. investigators believe in this moment, high voltage entered the center wing fuel tank igniting the warm fuel vapors. >> that ignition caused an overpressurization of the tank

that blew out the forward panel of the tank. you can see the indentation where it's very clear how it slammed down and there's a very clear mark. in that position we had fract e fractures that went down into the fuselage because of the pressurization of the airplane itself. that crack ran very rapidly around a portion of the lower fuselage. that caused the nose to detach from the rest of the aircraft. it fell off. if you drop the weight off the front, the center of the gravity goes back, the airplane will nose up. it will climb and go up. engines are still producing thrust. >> the aircraft entering a steep climb ascending between two and 3,000 feet. 42 seconds after the initial explosion, the left wing separates, spraying unburned fuel and igniting a second fireball. the wreckage, with passengers inside, plunges to the surface of the ocean.

the braeakup of flight 800 provides explanation for one of the most confounding aspects of the investigation, the eyewitness accounts. many described an ascending streak of light moving to a point of a large fireball that then splits into two. >> then the fireball. >> what's really interesting looking at witness statements was how many witnesses reported they heard the explosion ak looked that direction and saw the fire coming down. now, you take a look at the distance between the speed of light and speed of sound, it's quite clearly the explosion happens some time before they heard it. so when they heard the explosion, that already happened some time ago. so they turn and look they see the aftermath. they are seeing the fire after the explosion. they didn't see the initial event itself. >> investigators believe that

the streak of light that eyewitnesses describe is the main fuselage still climbing after the initial explosion, despite the ntsb's findings, theories persist of a bomb or missile attack on twa flight 800. >> it's unfortunate that a small number of people pursuing their own agendas have persisted in making unfounded charges of a government coverup in this investigation. >> i looked back and i am in awe of the cooperation and coordination of the thousands of people that were involved and touched this investigation. that's why i feel so strongly when anyone questions the patriotism or the responsibilities that were exercised by the investigators of twa 800. everyone understood that 230

lives had been lost. and it was up to them to do the very best they could to answer the question why. >> as a result of the ntsb's findings, major safety improvements are implemented with both aircraft design and maintenance. >> we now have systems in center fuel tanks so if there's not fuel in them that there's an increased amount of nitrogen which is non-explosive, that is manufactured on the airplane and then directed into the fuel tank. aging aircraft wiring maintenance programs have been significantly improved. that's a direct result. >> for the families of the victims, the tragedy leaves to the passage of the family assistance act, forever changing how loved ones are treated after transportation disasters. >> families will know exactly where to go and who will speak for the government when they have lost a loved one.

>> it took the events of twa flight 800 and the action of president clinton to ensure that their loved ones were given the proper respect when people have a loss and a tragedy like that. >> coming up -- >> descend. descend. >> two jetliners on a collision course. >> the closure rate is 16 miles a minute. you could not visually avoid the collision. >> the devastation will spur a deadly act of violence. >> this vigilante approach is an impediment to aviation safety for all of us. ahhh the sweet taste of victory! prilosec otc. one pill each morning. 24 hours. zero heartburn. ♪ (music pl ♪ throughout) uh oh. what's up? ♪ ♪

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july 1, 2002. dhl flight 6111 flying from italy to belgium. the two pilots of the boeing 757 cargo jet receive clear answer to climb to 36,000 feet as they pass through german airspace. at the same time, flight 2937 is in route from moscow to barcelona. the russian airplane is being chartered for a school trip. on board are 60 passengers, mostly children and nine crew members. the flight enters german airspace flying at 36,000 feet, the same flight level as the dhl cargo jet. the two airplanes are on a collision course. despite being over germany, the airspace is controlled from zurich by the private swissair

space control company skyguide. air travel controller peter neilson is the only person handling the airspace. his colleague has taken a break leaving him to monitor two screens, several feet apart. this is against regulations. but a common practice known and tolerated by skyguide management. on one screen, neilson is busy co-order naordinating the arriv delayed air bus. he doesn't notice there's a conflict between the russian airplane and the dhl jet. >> the controller was overloaded. he had a lot of responsibility. an overloaded controller is more prone to make errors. >> to make matters worse, neilson doesn't realize the ground-based optical collision warning system which alerts him to imminent collisions has been switched off for maintenance. in the sky, the two airplanes are less than a minute from

reaching each other. when an on board system sounds an alert to both crews. >> the system is one of the great technological innovations in aviation safety. >> traffic. >> it provides the crew not only with a display of a potential conflicting airplane, it also provides commands that ensure separation. it's a very, very smart system. >> on board the dhl cargo jet, it instructs them to descend. the crew responds immediately switching off the autopilot and beginning a accidedescend. the russian jet hears a different one. >> they coordinated to maximize separation. for system to work, both pilots

have to follow the commands. >> when neilson discovers the two airplanes are in danger, he contacts the russian crew. unaware that the system is issuing an advisory to climb, he instructs them to do the opposite and descend by 1,000 feet. >> when you have conflicting commands, there is a short interval which the decision is which one are we going to follow? >> it was not a fully implemented standard around the world where when the automated system said to take corrective action the pilots automatically followed without question. russia, their policies and procedures basically told the pilots that the air traffic controller has prominence or precedence, not the automated system. sg >> the russian crew is conflicted but they follow the instructions of air traffic control and begin descending.

>> you have one flight crew following the automation. you have another flight crew who is following instructions by the air traffic controller. now you have both airplanes descending. instead of avoiding each other by one climbing and one descending. >> the dhl cargo jet and the russian airplane are closing in at incredible speeds. >> you are talking airplanes that are moving basically four or five or 600 miles an hour. when they approach each other or converging, you can have a closure rate of anywhere from seven, 800 miles an hour to well over 1,000 myles an hour. >> the closure rate is 16 miles a minute. it's faster than most people can imagine. >> all of of a sudden now, decision making is very compressed because you don't have a lot of time. >> in the dark of night, the pilot's visibility is less than seven miles. >> from the time that you could

see the airplane, recognize it was a potential conflict for collision and avoid it, there wasn't enough time. the airplanes had physically covered so much ground that you could not visually avoid devast. and the investigation takes a deadly twist. >> it was a crime in my mind of almost unimaginable magnitude. raise your hand if you've got savings whiplash. you know, "save $500 bucks over here." "no, save $300 bucks over here." well, esurance was born online, and built to save. that's auto and home insurance for the modern world. esurance, an allstate company.

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traffic, traffic. >> a dhl cargo jet and a russian chartered flight with 69 people onboard, most of them children on a school trip, are on a collision course. the onboard traffic collision avoidance system or t-cas has issued coordinated commands. >> climb, climb, climb. descend, descend, descend.

>> unaware of the t-cas commands, the air traffic controller instructs the russian crew to also descend. now, the two airplanes are seconds from disaster. by the time they see each other, it's too late. at nearly 35,000 feet, the two airplanes collide at almost a right angle. the dhl boeing 757's vertical stabilizer slices completely through the fuselage of the russian airplane. many of the passengers are pulled from the aircraft as it plunges toward the ground. in the nose of the airplane, the crew loses consciousness from the high-speed fall. the dhl cargo jet has lost more than 80% of its vertical stabilizer. the pilots struggle to control the aircraft for another two minutes before they crash.

the airplanes strike the ground north of the town in germany with some pieces of the wreckage landing only feet from houses. no one on the ground is injured, but all 71 people onboard both airplanes are killed. nearby, the directors of a school for children with special needs hear the crash. >> translator: i heard a loud bang and thunder and i thought, strange, is that a storm, but it couldn't be really. >> translator: i looked out and saw what looked like a rocket and a column of fire falling to the earth. >> translator: this is the area where the people found their death. most of whom were children, in a strip from here, scattered through the woods. >> accident investigators began a long process of collecting and analyzing the wreckage of the boeing 757 cargo jet and the

russian airplane. preserved in this hangar. >> translator: we are basically standing on the roof of the plane and over there, we can see the left wing of that plane. and here, you can see massive collision marks due to the contact with the vertical tail of the boeing 757. and if you look here, you can see red color that matches the red color of this of the boeing. >> investigators determine that if the tcas commands had been followed by the crews of both airplanes, they would have avoided a collision. >> technically, if they both followed the tcas system in their respective aircraft, one would have climbed, the other would have descended and they would have avoided the conflict by vertical separation. >> investigators also conclude that shortcomings at sky guide, the swiss air traffic control system's supervising the flights at the time of the accident,

played a significant role. >> i don't find the word actually to describe the shock we have, i have, and the deep sadness we have, the whole crew of sky guide. >> only one air traffic controller, peter nielsen, was managing the air space at the time of the incident. he receives medical attention due to traumatic stress. but some people, like vitale, place the blame on nielsen himself. the man loses hihis wife and two children in the accident. a year and a half after the crash, a shocking act of violence. he travels to nielsen's home in switzerland and stabs him to death. >> this individualen a vigilantn impediment to safety for all of us because this action of the air traffic controller was not a willful disregard of procedure.

that gentleman that evening did the very best he could with what he had. for someone to take it upon themselves to commit a murder as a result of this, it goes counter to everything that i know in aviation safety. it goes counter to everything that all of us in aviation safety strive to do. it was a crime in my mind of almost unimaginable magnitude. >> he is convicted of the murder in 2005. but two years later, he's released from prison after the courts rule that his mental condition at the time of the murder was not sufficiently considered at sentencing. >> translator: i want to express my gratitude to all russian people for their support. having served in prison, i did not feel like i was without -- >> three of the four managers at sky guide are convicted of negligent homicide and given suspended prison terms of 6 to 15 months.

the fourth is ordered to pay a fine. sky guide says they no longer use the single manned operations that violate regulations. >> one of the things that was really examined in this was the work load of the controller and his diversion of attention. when it came to actually identifying the conflict and then providing timely conflict resolution prior to the event. >> the accident leads to a clear defining of the role of tcas. pilots around the world are now trained to give tcas advisories priority over the instructions from air traffic control. >> this accident showed the critical importance of a worldwide standard when we're talking about the technologies, particularly predictive technologies so that all of the pilots respond the same way and that way you don't have unexpected results like we got here.

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