HOW an Impossible Failure CRASHED this Boeing 767!

a Boing 767 is climbing out over the dense jungles of Northern Thailand the pilots are settling into their seats for the long flight ahead when suddenly a warning related to the aircraft trust traversa system appears this is a start of a terrifying chain of events that the aircraft manufacturer didn't even think was possible stay tuned 30 20 10 on the 26th of May 1991 a crew from laa air was getting ready for a two-leg flight bringing them from kitak airport in Hong Kong toward Bangkok in Thailand and then finally towards their home base in Vienna Austria this was part of a three times weekly service that laer was doing between Bangkok and Vienna and the aircraft that was being flown was a Boeing 767 300 that had been purchased new to Lou air only about 2 and 1 half years earlier in October 1989 this aircraft was a long range version of the Boing 767 and it was equipped with two pret and Whitney 460 High bypass turbo fan engines these engines were state-of-the-art they were very very efficient but the way that they were constructed is going to have a major impact on what's about to happen so we're going to have to become a little bit technical now a high bypass turbo fan engine is basically an engine where the majority of the thrust that is pushing the aircraft forward is produced by the big fan in front of the engine rather than the air that passes through the core and the burn Chambers in the case of the pratton Whitney 460 engines the bypass radio was about 5 to1 meaning that there was five times as much volume of air that passed the bypass duct of the engine than what passed through the core of the engine this High bypass ratio meant a lot better fuel economy and also much lower noise on these new engines because it turns out that using the fan to move a larger volume of air at a slower speed is much more efficient than trying to accelerate a smaller volume of air into higher speed this is by the way why all modern engine seems to be getting bigger and bigger but that's a slightly different story another consequence of this shift in design was that the engine trust reverses could now be constructed differently on older type of jet engines the reverse trust was constructed by two buckets being extended and then deployed into the core airf flow basically redirecting the whole core air flow into a forward angle but with these new high bypass engines it was found that it was much more efficient to use two translating sleeves that would move back and they would then extend blocker doors into the bypass duct that would redirect the bypass flow forward through some fixed Cascade veins and that would create the reverse Trust however another consequence of this was that the reverse trust was now being created in a slightly different place while in the old engines the reverse trust was being created at the very back of the engines now the reverse trust was being created much further ahead and that is going to have an impact in what's about to happen but why is reverse trust so important well as the aircraft kept becoming bigger and heavier and started to be able to fly during all sorts of different types of weather it became very apparent for the industry that the aircraft needed more than one way to decelerate of the landing or doing a rejected takeoff the trust reverses created a different type of braking than what the wheel brakes would and it turned out that especially during operations on wet or slippery runways the reverses were extremely important and even if they operated the aircraft on dry runways the reverses helped to take some energy away from the brakes which meant that the temperature of the brake discs could be lowered substantially now the reverses on Commercial aircraft were only certified to operate on the ground and because of that the aircraft manufacturers had built in several redundant systems to make sure that they couldn't be deployed once the aircraft was Airborne on the Boing 767 this was accomplished bya a safety mechanism that connected the weight on Wheel switches of the aircraft those are switches that can feel if the aircraft is on the ground or if it's Airborne was connected connected to two electrically activated hydraulic valves that both independently could make sure that the U trust reverses remained closed whilst the aircraft was Airborne the first valve was called a hydraulic isolation valve the HIV and it received signals from the weight on Wheel switches and when the weight on Wheel switches indicated that the aircraft was Airborne the hydraulic isolation valve just cut access from hydraulic fluid into the trust ravs mechanism and this was true any time that the aircraft was Airborne except when a system called the Resto circuit was active but we'll get to that later on if for whatever reason the hydraulic isolation valve would malfunction during flight and allow hydraulic fluid into the trust reversus that would send a warning to the pilot called reverser isolation notifying them that this was going on remember that now following the hydraulic isolation valve was a second weld called the directional control valve the dcv the directional control valve then directed hydraulic fluid to either deploy or close the trust reverses and the directional control valve was defaulted into the closed position so together these two valves were built in a way that should ensure redundancy to keep the trust rsus closed whenever the aircraft was Airborne on top of this the engines were constructed to automatically reduce the thrust on the engine back to idle in case it felt that any of the trust revers sleeves was starting to move but of course no system is completely foolproof and that had been proven by a couple of uncommanded trust revers deployment in flight on some other aircraft types including the dc8 the dc10 the Boeing 707 and the Boeing 747 and because that had happened the FAA had mandated Boeing to before certification prove either through flight tests or inlight modeling that the aircraft would be able to be handled properly in case a trust traverser would deploy in Flight those tests and models were built based on a couple of assumptions namely that this trust revers deployment would happen to an aircraft which was at a relatively low both altitude and air speed and the reason it was made like that was because that was seen as the most critical scenario because if the air speed is low it means that the um effect of the flight control surfaces would also be lower and that would be detrimental when it came to handling the effects of the asymmetric trusts that the trust reversal deployment would cause and also the loss of lift on the wing that it happened the test and models also assumed that the engine would be back at idle trust before the trust raver deployment event would happen and that was because of the way that the engines had been designed that the trust ravs sleeves shouldn't be able to start moving unless the engines were first back at idle with all of these assumptions met the model showed that the wing that was associated with the deployed trust traverser would only lose about 10% of its lift due to the air that was now being forced forward by the trust traversa disrupting the air flow at the Leading Edge of the wing this would cause a moderate roll and together with a yaw that was induced by the asymmetric trust this would only lead to moderate problems with controlling the aircraft something that was well within the capabil ities of a trained pilot on the 26th of May the day started just like any other day for the crew the pilots met up in the crew room in Hong Kong and started going through the flight plan the uh notps the weather and all of the other briefing material and once they were done with that they went they talked to the cabin crew and then together they went out to the aircraft when they came into the aircraft the captain went through the technical log and the technical status of the aircraft was perfectly fine it was perfectly airworthy now if the captain would have looked back through the technical history of the aircraft he would have noticed that there had been some work carried out on this aircraft by the technical department specifically there had been several instances of fault messages being sent from the leftand trust Traver these were minor fault messages but the maintenance department in La had been troubleshooting this on and off for the last 6 months or so they had followed the fault isolation manual that Boeing had provided to them and that had led them to replace some of the components inside of the trust DSA that would work for a little while but after a few flights similar fault messages would start reappearing again now because these fults were indicated as minor and not critical the dispatch deviation procedure guide actually allowed the aircraft to be dispatched and to fly with these fa codes for up to a maximum of 500 hours before it had to be rectified and every time that they did something that rectified the fault these 500 hours would be reset so this was why the aircraft had been flying with these reoccurring fault messages for the last 6 months the technical engineering department was not happy with this though so they had started to inspect all of the electrical wire bundles that was going out to the left-hand truster us to see if maybe there was something in there that was causing these fault messages to appear but since this was not a mandatory inspection and not part of the normal maintenance schedule they did this on and off and meanwhile the aircraft kept flying so even if the captain would have gone back through the tech log and seen that this maintenance work had been carried out and was going on it is unlikely that he would have reacted to it because according to the tech log it was fully airworthy with no limitations whatsoever the captain of the flight was a 48-year-old American citizen with about 11,750 hours of Total flight experience he was assisted by a 41-year-old first officer with just over 6,500 hours and together with them were eight cabin crew members on this flight on the first flight from Hong Kong over towards Bangkok the first officer was Pilot Flying they tax it out in kitak took off completely normally and proceeded to fly over to Bangkok without any indication of any type of problems they landed on time according to schedule tax it into their stand where they proceeded to do a normal turnaround uploading more fuel passengers and cargo getting ready for their flight back towards Vienna but before we get into that flight which is going to turn out to be the accident flight I just want to share this exclusive offer to you from my sponsor this video is sponsored by Nord VPN come a little bit closer closer I'm going to tell you a secret I can be anywhere I want within seconds Canada the US Sweden Japan you just name it a platform is not available in your country well then 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be Pilot Flying the pre-flight setup the walk around and all the general preparation was completely normal and at time 1602 that's 2302 local time the aircraft received its push back clearance and push back from the gate to start a taxi out for departure on Runway 21 left in Bangkok on board the aircraft was 213 passengers eight cabin crew members and the two pilots and at time 2315 La airflight 004 started rolling down Runway 21 left for takeoff the takeoff was completely normal they started climbing initially to 7,000 ft and turn towards the Northwest the weather in the area was quite good it was a little bit cloudy temperature of 26° with some light winds and some forecast of thunderstorms in the general area but nothing indicated that any thunderstorms were close to the flight path of flight 004 after takeoff the first officer contacted the Bangkok departures ATC frequency the flight was then cleared to continue to climb to 11,000 ft and turned towards a waypoint called Limbo this was read back by the first officer who was then told to contact the next departure controller the new controller told the flight to continue climb to flight Level 310 that's 31,000 ft and continue on the flight plan route the flaps were retracted as per normal procedures and once the flaps were up the first officer completed the off takeoff checklist and he then started to complete the flight plan to fill in the actual departure time to calculate the times over each Waypoint and the fuel they could expect at each Waypoint and then once he was done with this he passed on those figures onto the uh ground controller the operations controller in Bangkok for floud air so that they could follow the progress of the flight about 4 minutes and 45 seconds into the flight the first officer suddenly exclaims that keeps coming on referring to a left reverser isolation warning now the way he says it indicates that this warning must have been coming on and going out a couple of times before he actually says something about it now the do you remember what the reversal isolation warning actually means exactly this means that the hydraulic isolation valve that keeps the hydraulic fluid away from the trust reverser mechanism is now open in Flight the captain acknowledges this and tells the first officer to please take out the quick reference handbook non-normal checklist for this specific failure the first officer does so he finds the checklist but when he starts reading the checklist it doesn't really have any action items it gives a little bit of information about the fault and then it says that additional failures might cause inflight trust daversa deployment It also says that the pilot can expect normal operation of the trust daversa of the landing this likely reassures the pilots because anytime that a curate checklist doesn't have any action items in it and doesn't tell the pilots to land at the closest suitable airport it basically means that the failure is not that critical and the fact that the checklist just casually refers to an additional failures might cause an inflight deployment of the trust reverser um that just says that because remember there's still the directional control valve that is supposed to keep the trust reverses closed and the inflight testings that have been done prior to the certification of the aircraft has shown that even if the trust reverses doeses deploy it should be okay easily handled by the pilots now there is an additional checklist for an actual inflight deployment of the trust reverser and that checklist basically just tells the pilots to shut the um Associated engine down to minimize the effect on the reversa the pilots now keep discussing this indication as they're climbing away further and the first officer suggest that maybe they should contact the handling frequency in Bangkok to tell the engineering department that they have this problem and see if they have any guidance for them the captain says that that's a great idea contact them but tell them that it's likely moisture or something because the indication keeps coming on and off all the time now I understand why the captain thought this because a lot of warnings in an aircraft is triggered by micro switches these micro switches are monitoring the position of certain components and sometimes moisture or contamination can get into these micro switches and make them give faulty warnings actual fault tends to be more permanent in nature so when you have a small warning like this going on and off blinking like that given the amount of information that the captain knows at this point I would probably have thought the same in any case the aircraft continues to climb up towards 31,000 ft that they' been cleared and a few seconds later the first officer remarks to the captain that it looks like he needs a little bit of left trim what the first officer likely means is that he can see that the steering wheel is slightly displaced towards the left this can happen when there is some unexpected drag on one side of the aircraft in this case on the right hand side that causes a little bit of a yaw and the autopilot responds to this by putting Aeron in against that side to make sure that the aircraft keeps flying straight ahead but obviously flying with aons like that is not the most economical thing to do so what we do is that we have a little Roder on the back side of the main Roder that you can displace in order to counteract that yaw that will then Center the steering wheel and the aircraft will continue to fly straight ahead but in a more clean configuration now this remark is unlikely to have anything to do with what's about about to happen next about 4 and 1/2 minutes after the first officer made a comment about the trim this is 15 minutes and 1 second into the flight the first officer suddenly exclaims oh the trust revers is deployed at this point the aircraft is at an altitude of 24,700 Ft climbing with a speed of mac. 78 and with the engines producing full climb thrust the next thing that can be heard on the voice recorder is sounds similar to the aircraft shuddering and a metallic snap the airra now enters into a rapid Roll To the Left accompanied by a violent pitch down and within seconds several warnings can be heard on the copit voice recorder including the altitude alert and several M ACC caution warnings a second metallic snap can then be heard followed by the captain exclaiming Jesus Christ followed 12 seconds later by the captain saying here uh wait a moment and then 5 seconds after that damn it evidence indicates that it took the pilots approximately 10 seconds to shut the left engine down but at that point it was already too late as this is all happening you can hear on the copete voice recorder how the background noise is steadily increasing indicating a higher and higher indicated air speed this is then later accompanied by a continuous overs speed warning but why is this happening the aircraft is supposed to be controllable even if one of the trust reverses are deployed well it turns out that when the modeling was done it was based both on a much lower air speed about 200 knots and this aircraft is actually making mac.

78 and it also assumed that the engine would have been spooled back to idle before the reverse trust was activated in this case whatever failure that caused the trust reverser sleeves to start moving backward did so while the engines were still producing climb thrust and remember how we were talking about these new reverses they produced trust a little bit further forward on the engines well this meant that as these crust reversus sleeves were now moving backwards they produced an enormous plume of reverse air that came out just in front of the leading edges of the Wings likely reducing the lift available on that wing with as much as 25% not the 10% that the models had shown this sudden and violent onset of reverse Trust on the left hand side initiated a 28° per second roll towards the left together with a violent yaw due to the asymmetric trust situation the Pilots would have had to immediately initiate full right Rudder and full right Aon to try to counteract this together with reducing the thrust on the operating right engine to minimize the trust asymmetry but here the pilots would have faced their next hurdle which is that as this descent initiated they were already at a speed of mac. 78 and as the speed now continue to increase as we could hear from the cockpit voice recorder and the overs speed warning it meant that the pressures and the stresses on the aircraft would have built up enormously and that would have meant that the pilots would have had to be very very careful in order to not overstress the aircraft structure as they tried to both maneuver out of the situation and pull the aircraft out of the dive simultaneously as the aircraft is now accelerating and getting closer to the speed of sound the effect of the flight controls would start to become less effective due to elasticity and aerodynamic Mac effects and if you put that together with the fact that they're still suffering from asymmetric trust from they now deployed the trust traversa it together means that this situation became completely uncontrollable within seconds after the uh trust reverser deployed what now follows is a terrifying example of what happens to an aircraft when it exceeds its maximum both speed and maneuvering loads we don't know exactly how high the speed became in the and but we do know from the eec memory on the left hand side that it recorded Mac 0.