Unstable Airplane Design! The Incredible Story of China Eastern flight 583

this video is created with support from betterhelp turbulence that's probably the one word that strikes the most fear Into the Heart of nervous Flyers everywhere but is it actually dangerous and if so in what way cabin crew always mentioned that it's important that you keep your seat belt lightly fastened at all times and today you'll find out where that instruction actually comes from the time is 0110 Hawaiian Standard time over the Pacific Ocean on the 6th of April 1993. a McDonald Douglas md-11 from China Eastern Airlines is cruising smoothly at 33 000 feet heading eastbound towards the United States the flight started in Beijing and after an intermediate stop in Shanghai it was now headed towards Los Angeles International Airport and at the time of the accident its position was about 950 nautical miles from shimia in Alaska on board the aircraft there were 235 passengers and 20 crew members including two full flight Crews of eight pilots in total the aircraft was about five hours into its flight from Shanghai and the pilots would flown the initial part of the flight had now gone back to the crew bunks to get some rest this meant that the relief crew consisting of a captain first officer flight engineer and a radio operator was now in short of the flight and had been so for the last 20 minutes preceding the incident the flight had been perfectly nice and smooth up until this point with no failures experience and with nice weather forecasted ahead of them the aircraft was cruising along above the clouds and at a manually selected speed of Mach 0.82 and at that altitude that equated to about 298 knots of indicated AirSpeed this was a normal Cruise speed for the md11 but quite quick if you compare it to the Boeing 737 that iFly we normally never exceed Max 0.81 in any circumstances but the md-11 was a really quick bird partially because of its high sweep angle of its wings which enabled higher Mach numbers Captain was 42 years old and had a total experience of 8535 hours of which 1 341 was flown on their relatively new md-11 on this slide he was training the first officer to watch command and was therefore sitting in the right seat whilst the first officer was sitting in the left the first officer was 43 years old and very experienced with 9714 hours of Total time but only 199 of those have been flown on the md-11 he had received his initial type rating on the MD about five months earlier in December of 1992. the flight engineer was 41 years old and had similar experience as the first officer and we don't really know the experience of the radio operator the md-11 that they were flying was a beautiful tri-engine aircraft built as a successor to the popular DC-10 it had received its FAA certification back in 1990 and it Incorporated quite a few changes from the design of its predecessor in the cockpit it used six castle Dre tube displays instead of the old steam gauges meaning that it had a full electronic flight instrument system or ephes which effectively eliminated the need of the flight engineer but this was still a relatively new system for China Eastern which is likely why they were still operating with the four pilot cockpit crew another change in the md-11 was that it had a slightly smaller overall tail plane than the DC-10 had and it was designed this way to help reduce its drag and give better fuel economy this reduction in size had been accomplished partially by reducing the amount of lift the horizontal stabilizer needed to produce in Crews by moving the center of gravity of the whole aircraft backwards with the help of fuel tanks situated inside of the horizontal stabilizer now I know that this might sound a bit confusing but it is a really important factor in this accident so to explain it let's look at some theory behind aircraft weight and balance as well as some aerodynamics an aircraft is kept stabilized and controllable in Flight by balancing several different forces if we concentrate on the pitch stability you can try to picture the aircraft like a big Teeter board the point the aircraft is pitching around is called its center of gravity which is the point where you can imagine that the whole mass of the aircraft is concentrated if you imagine trying to balance the aircraft using one massive finger that would be the point that you would need to use but of course if we didn't have some kind of stability added to the design well then a passenger moving inside of the aircraft would change the center of gravity and the aircraft would start pitching either up or down obviously that's not what we want we want the aircraft to be stable and controllable even if the center of gravity moves around slightly and this is where the horizontal stabilizer comes in the horizontal stabilizer is built exactly like a small wing but its lift is pointed downwards instead of up because of this it's working opposite to the direction of the huge lift created by the wings so if you now go back to that picture of the aircraft acting like a teeter board started to picture the lift of the aircraft acting just behind the center of gravity with an upwards Force now if there was nothing to counteract it this force would cause the aircraft to pitch forward right exactly and that's why the horizontal stabilizer is creating an opposite Force but a lot further away from the center of gravity meaning that it has a longer momentum arm to counteract that pitch and keep the aircraft level this is how an aircraft keeps stabilizing pitch throughout the flight envelope and we use the movable stabilizer to increase or decrease that downforce depending on how people are seated in cabin or how the center of gravity moves throughout the flight as we burn fuel for example so moving the stabilizer will trim away any pitch tendencies that we Pilots feel as we're controlling the aircraft and that's why we refer to it as trimming the aircraft so what does this have to do with the md-11 then well I'll tell you everything about that just after this very few things are as important today as awareness and support of your own Mental Health whether you're a nervous flyer who is struggling a bit with anxiety or a professional who just wants someone to talk to about your role you should definitely check out today's sponsor betterhelp the world's largest online therapy service with better help you can connect to over 30 000 licensed and experienced therapists who are specialized in supporting individuals just like you and me they can provide you with help with for example fear of flying but also with things like procrastination at work or just finding ways to improve your overall emotional well-being most people spend hours in the gym or on the treadmill every week so why not give your mind the same kind of attention better help services are completely online allowing you to access them from the comfort of your own home and at the time that suits you it's really therapy at your own terms getting started is super simple you just answer a few questions about your needs and goals and better help will then match you with the perfect therapy super fast you'll then be able to contact him or her through text chat phone or video call whatever makes you the most comfortable and you can also change your therapist if you want to everything to give you the best possible experience so if you are a nervous flyer or just want to keep up the maintenance of your mental health then go to betterhelp.com mentorpilot and receive 10 of your first month thank you better health now let's continue the problem with a downwards directed force from the stabilizer is that the bigger that force is well the more that downforce ultimately needs to be compensated by the upwards lift from the wings and this creates drag which means a higher fuel burn engineers at McDonald Douglas had figured out that if they could move the center of gravity further back in cruise by pumping fuel into tanks in the horizontal stabilizer well then they would need less downforce from the stabilizer and could therefore both say it fuel directly and also make the whole tail a bit smaller reducing the drag even further now you might say that sounds awesome why doesn't everyone just do that well it also comes with a couple of small downsides basically an aircraft is a perfect combination of compromises everywhere and this is no exception from that if you move the center of gravity closer to the center of lift the amount of downforce needed from the stabilizer will indeed be smaller but so will the overall pitch stability of the aircraft stability is the aircraft natural tendency to return back to a neutral state after a disturbance and it's divided into Dynamic stability which has to do with the pilot stick Force which should increase if the aircraft moves away from the trim their speed and static stability which is what we're talking about here the md-11 had been constructed to fly in cruise with almost no static stability meaning that a sudden flight controlled Movement by the pilot could cause very abrupt pitch changes this is actually how most modern fighter jets are constructed today it makes them extremely maneuverable but also very hard to manually control without some type of augmentation system or flight control support computer the engineers at McDonald Douglas knew this so they had also created a longitudinal stability augmentation system called Elsas to help simulate the stability by basically acting like an always active autopilot altitude hold system now Elsas could be overridden by the pilots by applying a manual stick force of around two pounds or just under one kilo but it would resume immediately if the fourth on the stick would be released it would then gently try to get the aircraft back to level flight by halving each subsequent pitch movement until it was fully level right I understand that your heads might be spinning right now but what all of this basically means is that the md11 was much less stable in Pitch than other comparable aircraft at the time making it harder for the pilots to control in case they needed to hand fly it while they were in Cruise okay so the next system that I need to talk about is the flap and Slot system in order for an aircraft to be able to fly well in both the high speed and low speed regime we basically need to be able to change both the form and surface area of the Wings in high speed flights the wings needs to be as clean and uncurved as possible but as we slow down during both the takeoff and Landing we need to increase its surface and curve it in order to generate as much lift as possible from The Little Speed that we have during those segments we do this with the help of high lift devices which are the flaps that extend at the back of the Wings and slats which are devices extending from the wings leading edges here we will focus on the slats the slots when extended both effectively extends the Wing's overall surface but they also include slots which lets part of the airflow through and up on top of the wing the total effect of this is that it helps allow flight with a higher angle of attack which is exactly what we need during the takeoff for landing on the md-11 each Wing was equipped with eight slots grouped into two inner slats and six outer slots when activated by the flap slab handle in the cockpit the two inner slabs would hydraulically start extending first and after about three seconds the movement of the inner slot would then triggered an extension mechanism for the outer slots which would then start extending the outer six slots also had an out to extend function which would activate if the aircraft approached a low speed stall with the slats retracted now when it comes to the actual slat activation handle in the cockpit it will become very important in this story because when the md-11 was being certified it was found that a breakage of the slab activation cable would default the slats to the retracted position which was not ideal the FAA wanted the system to instead default to a slap extension if the cable would break and to achieve this a combination of cable tension and spring forces was introduced to the system now the issue with that was that the flap slat handle now was under constant tension so if they handle would for some reason move out of its up retract detent it would quickly move to slat extension by itself and this brings us back to this early morning over the Pacific Ocean the aircraft kept streaking across the sky the 14 cabin crew members in the back had just finished the meal service and was now dampening the lights for the in-flight movie the flight had been smoothed up until this point so the fast and seatbelt sign was not illuminated and some passengers were moving around to stretch their legs or use the toilets in the cockpit several small failures are not started occurring in the number two flight management computer which had caused the captain who was sitting in the first officer's chair to go into his CDU and reinsert some data that had gotten lost this was a very minor nuisance but it had likely alerted the captain a bit and he now started looking closer at the information that he had in front of him this is a quite typical pilot Behavior if one little computer bug appears it seldom comes alone so he was now actively searching for the next one and a small circled speed on his primary flight display caught his attention this speed was the FMC suggested economy speed and it looked far too low in his opinion so he again dove into his CDU to try to rectify that now we don't know why the economy speed was indicated lower than the captain expected it's likely that someone has just entered a lower than normal cost index during the pre-flight sequence which could have had this effect but we will never really know what is important here is that he was working with the CDU and potentially in a bit awkward way since this was not his normal seat and he would need to use his left rather than his right hand to do this it is quite likely that during this work he accidentally bumped his hand or arm into the flap slat lever just enough to move it out of its detent and like I explained before this was all that was needed for the flap lever to now move away from the up protracted position and initiate the slapped extension now this was far from the first time that this had happened during the time from the md-11 certification in 1990 and up to this accident there had been 10 different instances of inadvertent slacked extensions during various phases of light and because of that McDonald Douglas had implemented several service bulletins trying to deal with the problem including installing a type of gate on the flap d-10 but none of them had completely solved the issue this had led to the airlines implementing training modules for their pilots and how to avoid these inadvertent slot extensions and the captain had gone through that training just one month prior to this event anyway like I said as the flap slat lever moved out of its gate the tensioned cable now started moving and initiated the mechanism for the extension of the inner slats both Pilots were still likely looking at a CDU as this was happening discussing how to sort out that strange economy speed the first indication of something going wrong would have likely been a slight schroddering in the aircraft as the inboard slots now started extending into the airflow at the speed and Mach number much faster than they were designed for now because the inboard slots are situated relatively close to the aircraft Center of lift their extension didn't produce any significant change in Pitch but this was soon about the change the aircraft had just entered into a pre-programmed slower right turn and when the first three seconds at elapsed after the flap handle has been dislodged the extend mechanism now also activated the outer slats it's probably worth noting here that if the flap slot handle had been moved back into the retract position before those first two to three seconds well then the inboard slot would retract without the outboard slot starting to move but after that time the full extension of the slots was unavoidable and would go through the full extended and retract cycle even if the handle was moved back again as the buffeting now grew more intense the captain looked down onto his primary flight display and saw to his horror a wide downwards pointing Arrow next to the slot syndication and realized what was happening he quickly moved the handle back into the retract position but as he was doing so the outboard slabs were already extending now remember how I said that the inboard slots didn't have any real impact on the pitch of the aircraft well since the wings of the md-11 was very steeply swept in order to enable flight with high Mach numbers that meant that the outboard slats were positioned much more behind the center of gravity than the inboard slots were and that meant that whatever lift effect they had would cause much more of a moment difference than the inner ones under normal circumstances the slabs being extended would cause an increase in lift and therefore a slight pitch down momentum but in this case the slabs were being extended at a very high Mach number which caused the air to move in a completely different way than in the low speed regime basically at higher Mach numbers the air will not have time to properly adapt and Float around the object that is moving towards it this will mean that extending slots at the speed of Max 0.82 will cause a loss of lift instead of a gain and remember what we said about that Teeter board before yes if the lift from the wings now suddenly decreased behind the center of gravity but the downward force of the stabilizer remain the same well then the nose of the aircraft would start pitching up and that's exactly what now happened the autopilot was still engaged and started to input elevator to compensate for this pitch but it wasn't quick enough to compensate completely in order to avoid it this meant that the angle of attack the angle of the oncoming air now also started increasing rapidly together with some GE loading you know that feeling of being pushed into your seat the margins to stall are quite small at these altitudes and because the elevators of the md-11 was built largely from Composites they were really sensitive to stall buffeting so the stall warning system was set to activate quite early to avoid that what this all meant was that as the aircraft now pitched up the captain pushed the flap slot level down and started observing the aircraft response well the stall warning now started sounding together with a slight over-speed shine as the aircraft reached a maximum pitch of around 9.5 degrees pitch up now Pilots are trained to respond immediately to a stall warning and the first thing that we're taught to do is to unload the Wings by pitching down and that's exactly what the captain now did he started inputting on his yoke pushing it forward and by doing so he also disconnected both the autopilot and the stability augmentation system as it did so the elevator input would have gone from a quite modest autopilot pitch down input into a significantly bigger pilot induced one this started to reverse the upward pitch and quite quickly instead turned it into a pitch down momentum now anyone who's ever been in a roller coaster knows what happens when it shifts from a pull-up in a valley and moves towards the next Crest you will go from being pushed into your seat to feeling like you're going to be pulled out of it instead and what you are feeling there is the impact of positive and negative g-forces now I'm gonna hesitate to Guess that most people who have ever tried a roller coaster would have been quite happy about their seat belts and there's a very good reason for that in the back of the cabin this first upwards movement would have caused a positive G load of around 1.5 G meaning a 50 increase in perceived weight now that would not have been so bad it would likely just have felt a bit strange but what came next is what really started to cause this disaster because as the captain was now pitching forward the positive g-load quickly disappeared and now started to move into the negative Direction instead meaning that the passengers first started feeling weightlessness but then as the g-forces became negative anyone who wasn't wearing their seat belt was suddenly thrown up into the ceiling along with everything else in the cabin that wasn't tied down as the aircraft started pitching more and more forward the stall warning eventually disappeared but a small detail about the stalled warning system in the md-11 was that it was programmed to last about one second longer than the actual stall condition necessitated the thought behind that was to get the pilots to continue their recovery slightly longer and therefore avoid the potential secondary stall but of course in this case it also meant that the pitch down effort was being kept just a bit longer than needed the seatbelt sign was now activated most likely by the first officer but at this point it was already too late as the aircraft was now pitching down and the stall warning had disappeared the captain started to reverse the elevator input and pull the aircraft out of its dive but he used much more elevator input than was actually needed almost seven degrees of pitch up deflection this meant that as the aircraft reached its lowest point around -6 degrees it now started pitching up again causing another positive G load that would have brought everything in the cabin who was previously pinned up into the ceiling crashing down again the captain likely felt these positive G's and responded by pushing forwards likely to smoothen things out but remember at this point the aircraft would have had almost full ballast tanks in the stabilizer meaning that it had close to neutral pitch stability making pitch control really difficult if he would have just let go of the controls at this point the Elsa stability system would have likely intervened and stabilized the flight but instead the captain now saw that the pitch attitude that he wanted which was around two degrees pitch shop was very close this caused him to again pull slightly back on the controls to try and stabilize the pitch but he pulled just a little bit too much leading to another pit shop and another stall warning discourse the whole situation to once again repeat but this time with even bigger control inputs and pitch perturbations the second Pitch forward caused a negative g-force of minus 0.8 G again throwing people magazines bags and trolleys up into the ceiling before eventually throwing them back down again as the aircraft started pitching back up this was done followed by a third cycle every time becoming slightly more violent because of over controlling and also the fact that the pilots were now trying to maintain manual control at the same time as they were also being subjected to these alternating g-forces making it even harder since the stall warning kept going for that extra second every time it activated it meant that the corrections kept becoming larger reaching a maximum of 24 degrees pitched down during the worst cycle which also caused an altitude loss of around 5000 feet during that cycle the maximum g-load experience was about plus 2.06 G's and the minimum minus 1.24 G's after a number of perturbations the control inputs finally began to decrease leading to smaller and smaller cycles and eventually the aircraft leveled off at around 28 000 feet after having accelerated to an airspeed of 364 knots where an overspeed warning was also heard in the cockpit 94 seconds after the inadvertent slat extension the aircraft seemed to be finally under control and the pilot started climbing back towards 33 000 feet and engaged the autopilot again unfortunately we have no idea about what kind of conversations were going on between the four Pilots as this was unfolding because the cockpit voice recorder was found to be faulty with no usable recording having been saved the flight date recorder also had several issues with it which meant that only partial data could eventually be retrieved now some of you might be asking how come that a trained fly crew was unable to handle a disturbance like this in a better way well as it turns out the crew were not trained in high altitude upsets of this kind nor in the handling of the aircraft with the stabilizer fuel tanks full the during these conditions the md-11 would have required significantly less pitch input than the pilots would have been used to both from other aircraft types and how it would behave during a lower altitude flight on top of that the small pitch input needed would have been in stark contrast to the way an approach to stall and Recovery maneuver would have been trained at the time in the back of the cabin it was now complete Mayhem the actual value of the g-forces had not been that exceedingly high but the fact that they had moved between strong positive and negative G's several times had caused several of the passengers to be thrown into the overhead bins seat packs armrests as well as other passengers when the pilots got into contact with the cabin crew they were told about the severity of the situation and that prompted the radio operator to at the time 0123 contact the Honolulu air traffic controller and request an immediate diversion to the nearest available airport about two minutes later he called up again and clarified that the emergency had to do with a sick passenger but then he further clarified that they had encountered severe turbulence and that there were multiple sick passengers on board and he wasn't overstating that fact in the back of the aircraft the cabin crew members who weren't severely injured themselves were now dealing with a true nightmare out of the 255 passengers only 97 were unharmed 96 had minor injuries and 63 had serious injuries mostly related to the head neck and spine the passengers most affected were those who had not been wearing their seat belts when this sudden roller coaster started Ore had been hit by other passengers or objects being thrown around in the cabin as the cabin crew used up all of the first aid kits they had the pilots were receiving radar vectors towards Shemia Air Force Base in Alaska the problem was that this airport was still too agonizing hours away as they progressed towards the new destination the pilots started dumping fuel to prepare the aircraft for landing this is something that larger long-haul aircraft often must do if they need to divert along the Route the reason for that is that their maximum takeoff weight is significantly higher than their maximum Landing weight and to make sure that the aircraft Camp would stand the forces from a landing the fuel is dumped to achieve a weight closer to or even under the maximum Landing weight the aircraft eventually executed an uneventful descent and ILS approach into Runway 28 at shami Air Force Base and at time 03 29 they landed safely and started taxiing in waiting for them on the apron were several aircraft from the American Coast Guard and navy who were ready to take the injured passengers to four different hospital in the Anchorage area unfortunately though two of the injured passengers ultimately passed away from their injuries litigation ultimately showed that even though the aircraft's cabin interior was severely damaged the aircraft structure in itself was completely undamaged and it was able to fly to a maintenance facility to undergo cabin repairs a while later the course of the accident was found to be inadequate design of the flap slat activation handle which had led to an involuntary slat extension at high altitude this had in turn led to the captain trying to stabilize the flight and respond to the stall warnings but due to reduced pitch stability of the aircraft and a lack of training his actions led to several large pilot-induced oscillations causing the injuries in the cabin this accident led to calls for a complete redesign of the flat slat handle on the md-11 as well as changes to the cabin Pas advising passengers to keep their seat belts Loosely fastened throughout the flight all md-11 Pilots were also to receive more training on the handling characteristics of the md-11 in Cruise flight as well as aircraft specific upset and Recovery training there were also recommendations to establish a minimum stall margin of 1.3 G's in the cruise phase for aircraft certified by the FAA similar to the rules already enforced in Europe at the time as is the case with all accidents and incidents this one has served to improve overall safety not only for passengers on the md-11 but for everyone else flying out there as for nervous Flyers this will hopefully show that it it's not turbulence in itself that we should worry about the aircraft is more than able to handle that instead turbulence injuries are more likely to be caused by simple things like not wearing your seat belt or stowing your hand luggage improperly if you are a nervous flyer and you feel like you need some professional support then consider using today's sponsor better help by clicking on the link below one try it out but if you instead feel like you only have some questions that you would like to ask well then you should check out my web app at app.mentorpilot.com and ask my AI assistant Aiden your questions you can also find aviation news flight information and much much more but the coolest features are there if you become a premium subscriber now check out this or this video next and if you want to support the work that we do here on the channel then please join my awesome Patron crew or buy yourself a t-shirt there are links here on 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Channel: Mentour Pilot

Views: 186,749

Keywords: Turbulence, Pacific Ocean, Beijing, Shanghai, Alaska, China Eastern, 583, MD-11, MD11, Flaps, Slats, mentour pilot, trending, plane crash, boeing, crash, disaster, storytelling, true crime, full episodes, investigation, documentary, entertainment, mentour now, Mentour Pilot Crash, Aircrash investigation, Seconds from disaster, Aviation explained, Boeing, Airbus

Id: SEMTJMSYYlo

Length: 31min 51sec (1911 seconds)

Published: Sat Jul 08 2023