Page Links: First Previous 1 2 3 4 5 6 Next Last Index Page
Tu.114
2025-06-15T21:17:00 permalink Post: 11902850 |
The electrical failure is rather a chicken-egg question.
Not knowing the 787, I\xb4d find it extremely hard to believe that a massive electrical failure would kill the engines. I gather from this thread that the landing gear retraction is driven by the electrically-powered Center hydraulic system. Retracting the gear is hard work for the system and it will put a strain on the two pumps and their supplying electric circuits, and the time of the alleged total power loss would seem to be in the vicinity of the suitable time to retract the gear. But if there was some freak epidemic failure this inflicted upon the aircraft electrics, it is hard to imagine that this would affect both engines. There are still the autonomous FADEC governing them that run on their own internal generators (with a small external power source from the main systems, should the permanent magnet alternators fail) and do everything they can to keep the engine alive. As long as there is fuel flowing into the feed pipes, the engine should be kept running by the FADECs, and that this does not require the large tank pumps at low altitudes has been established in this thread. Consequently, I\xb4d deem it plausible that the alleged power failure must have been a consequence of whatever happened to the engines. After all, the engines drive the available generators at this stage of flight, the APU with its additional generators is apparently not run for takeoff on the 787. I find it logically much easier to wrap my head around a situation in which an engine failure takes along the generators than one in which a massive, epidemic electric breakdown kills the engines. |
cavuman1
2025-06-15T21:33:00 permalink Post: 11902861 |
Potable/waste water leakage into the forward EE Bay is a potentially fascinating fit. Rotation sloshes water onto a critical wiring junction resulting in dual simultaneous engine shut down as well as cascading electrical failure throughout the aircraft. The hard part is thinking that Boeing's engineers would permit such a failure mode in their design. It would seem to require a substantial volume of liquid.
See tour of forward avionics bay, Boeing 787: May the victims rest in peace and their families find enduring comfort. - Ed 3 users liked this post. |
Pinkman
2025-06-16T09:17:00 permalink Post: 11903301 |
With the information we have accumulated so far, is the following a possible scenario? Normal departure up to VR, then a total electrical failure at lift off (possibly as the ground/air logic switches to air.) All hydraulics lost and cabin lights flicker plus RAT deploys. All fuel boost pumps fail so engines only have suction feed. Engines roll back. The aircraft seems to me to have gone too far to have suffered a total loss of thrust at lift off. There must have been some energy being provided by the engines? Such a system failure "can't happen", of course but nothing is impossible!
|
Feathers McGraw
2025-06-16T22:33:00 permalink Post: 11903844 |
I'd like to mention something that, while unrelated, does shed a bit of light on how computerised systems can misinterpret input data and take the wrong action. I spent 40 odd years as an electronics engineer involving complex systems, it can be surprising just how careful one must be in systems that sample data and then process it for decision making in software.
On August 9th 2019, there was a significant grid failure in the UK leading to load shedding (removing supply to many consumers, including Newcastle Airport) which started when a series of several lightning strikes in Hertfordshire caused a trip out of generators at Little Barford combined-cycle gas turbine generation plant. This was followed by the shut down of the power concentrator and grid connector from the Hornsea1 off-shore wind farm, significant changes in the grid frequency away from the acceptable limits which is what triggered further load shedding. The reason I mention it is that Hornsea1 going off line was due to the software that operated the concentrator/connector sensing large voltage transients due to the lightning strikes 120 miles away, however these transients were only of the order of 10us length spikes with nominal 20ms cycles at 50Hz on the grid. In old reliable grid equipment that had been in use for decades such spikes would have been ignored because the large rotating machine inertia would make them irrelevant. Other systems went into various states of shut down for protection reasons, some of the Siemens Class 700 trains had to be reset by the train crew, others required a Siemens engineer to drive to each train and reload its firmware. The train protection mode occurred because the grid frequency on the 25kV AC supply went below 49.8Hz, this was a programmed default and it turned out to have been a very conservative one, the trains could have continued to operate normally at even lower frequencies but someone decided to write the programs without actually testing what a sensible limit was. The whole very widespread problems this caused could have been avoided by not acting instantly on microsecond transients in a 50Hz system. Is it possible that the monitoring systems on a Boeing 787 also sample the electrical system voltages and currents at a relatively high frequency, and thus in the event of a transient of some type perhaps over-react to this event by taking precipitate action instead of waiting a short time before re-sampling again. I have seen a suggestion that an alternative explanation for the "bang" heard by the survivor in seat 11A might have been the sound of a Bus Tie Contactor closing, which in itself suggests something quite important relating to the electrical system. The 787 is unusual in that it uses variable frequency AC generators whose outputs are rectified and then inverted to other AC voltages and also quite high DC voltages, some in the 250-300V region. I hope that some hard information is going to come out from the investigators soon, but given that the flap mis-selection idea is effectively debunked and we know that the main undercarriage either started its retraction cycle with bogies tilting forwards or that falling hydraulic pressure caused the same thing to happen, then the only thing that fits the observed flight path is loss of thrust on both engines which could have either preceded or followed an electrical failure. We also know that the RAT deployed and in the relatively undamaged tail cone the APU inlet was open or opening indicating a likely auto-start of the APU due to the parameters to trigger that occurring. I would like to know how many tests of the electrical/computer interactions in 787 development involved arcing/shorting voltage/current transient testing. Is this the sort of thing that is done at all? The EECs (FADECs) in the engines are self-powered via magnetos and self-controlling in many circumstances, but perhaps something caused them to think that the thrust levers had been retarded, and such a thing might have been down to the effect of electrical transients on the various signals received by the EECs. I have read the original 65+ pages of the thread, but I have not seen any discussion of this particular idea. Maybe that is because the 787 is quite a significant departure from Boeing's previous design practices with totally different electrical systems, higher pressure hydraulics and no doubt other aspects as well. What do you all think? 15 users liked this post. |
Aerospace101
2025-06-16T22:38:00 permalink Post: 11903849 |
Truck forward tilt discussion
I previously speculated the forward truck tilt was proof the gear had been selected UP and the retraction sequence was interrupted.
I’m not so sure now and believe there is a different conclusion from this non-normal gear position. In normal retraction sequence the gear doors open almost instantaneously after the forward truck tilt. It does seem coincidental the tilt was completed while no indication of the doors opening is visible on the rooftop video, which would suggest hydraulic failure at that exact moment; this precise timing of interruption in the retraction sequence feels unlikely. So is there a more likely answer for the forward truck tilt that does not involve movement of the gear lever? I suspect it’s more likely that C hydraulics lost power prior to rotation, as a consequence the truck could not tilt rearward during rotation as it normally should. Therefore it’s probable it always stayed in a neutral or forward tilt position from the take off run until we see it in the rooftop video. If the gear was behaving normally, and the crew had omitted to retract, it should be hanging rearwards. Watch any 787-8 takeoff video and you can see at rotation all 4 main wheels stay on the runway as the aircraft rotates. Just after wheels up they tilt rearwards. It’s a very subtle position change. If the gear was always in a neutral or forward truck tilt position then this undermines the theory that retraction sequence was interrupted. It insinuates the C hydraulic and electrical failure happened prior to main wheels lift off. For this reason I believe we cannot assume that gear UP was selected nor that retraction was interrupted. I’m seeing lots of social media posts which suggest the forward tilt means gear was in retraction and I don’t believe it was now. I think the truck tilt position is key to understanding the timeline of system failures and whether the automatic RAT deployment was triggered by power failures or engine(s) failure. The question remains, did loss of center hydraulics happen before or after loss of thrust? Last edited by T28B; 16th Jun 2025 at 23:35 . Reason: white space is your friend, and is reader friendly 13 users liked this post. |
dragon6172
2025-06-17T01:30:00 permalink Post: 11903903 |
I previously speculated the forward truck tilt was proof the gear had been selected UP and the retraction sequence was interrupted.
I\x92m not so sure now and believe there is a different conclusion from this non-normal gear position. In normal retraction sequence the gear doors open almost instantaneously after the forward truck tilt. It does seem coincidental the tilt was completed while no indication of the doors opening is visible on the rooftop video, which would suggest hydraulic failure at that exact moment; this precise timing of interruption in the retraction sequence feels unlikely. So is there a more likely answer for the forward truck tilt that does not involve movement of the gear lever? I suspect it\x92s more likely that C hydraulics lost power prior to rotation, as a consequence the truck could not tilt rearward during rotation as it normally should. Therefore it\x92s probable it always stayed in a neutral or forward tilt position from the take off run until we see it in the rooftop video. If the gear was behaving normally, and the crew had omitted to retract, it should be hanging rearwards. Watch any 787-8 takeoff video and you can see at rotation all 4 main wheels stay on the runway as the aircraft rotates. Just after wheels up they tilt rearwards. It\x92s a very subtle position change. If the gear was always in a neutral or forward truck tilt position then this undermines the theory that retraction sequence was interrupted. It insinuates the C hydraulic and electrical failure happened prior to main wheels lift off. For this reason I believe we cannot assume that gear UP was selected nor that retraction was interrupted. I\x92m seeing lots of social media posts which suggest the forward tilt means gear was in retraction and I don\x92t believe it was now. I think the truck tilt position is key to understanding the timeline of system failures and whether the automatic RAT deployment was triggered by power failures or engine(s) failure. The question remains, did loss of center hydraulics happen before or after loss of thrust? In a normal retraction, the main gear doors begin to open before the truck tilt is complete (roughly when the gear trucks are "level", seen around 8-10 second marks of this video ). The nose gear doors open at the same time the main gear tilt starts (seen in Jetstar video linked below). It's too blurry in the video/stills of the accident aircraft to definitively say the nose doors are not open, but I'd say no. And it's pretty much a certainty that the main gear doors are not open. And finally I think it is also pretty clear that the main gear trucks are tilted down to the retract position. I have no confirmation of this, but I read (or heard someone say in a video) that the truck tilt actuator was a "single acting" actuator, meaning hydraulic pressure held it in the toe up position and it was spring loaded to the retract position. Which means if hydraulic pressure was lost due to loss of power to the electric driven center hydraulic system, then the main gear trucks would tilt forward on their own without moving the gear handle. The Jetstar burst tire video somewhat backs this up, in that the blown tire caused a leak to the center hydraulic system and an alternate extension was required (thus the reason the main doors are down during the landing). No hydraulic pressure means the main gear trucks remained pointing nose down during the landing. Video here Last edited by dragon6172; 18th Jun 2025 at 03:01 . Reason: Edit video links 3 users liked this post. |
hawkeye red
2025-06-17T06:10:00 permalink Post: 11903994 |
Just a quick question to any B787 jockey out there…will a total electrical failure initiate a full engine shutdown…???
|
TURIN
2025-06-17T06:26:00 permalink Post: 11904001 |
7 users liked this post. |
JPI33600
2025-06-17T10:01:00 permalink Post: 11904160 |
Not an avionics specialist, but electronics / software engineer here, with extensive experience in hardware fault tracking, protocol monitoring and software debugging in embedded systems : mods, feel free to delete this post if I am completely out of track (and thank you for the huge amount of work you've done trying to keep this discussion clean).
After I have read the whole thread, I think most of the community agrees about a lack of engine thrust being the cause of the crash. Searching in that direction, I'm trying to "think out of the box", discarding the usual suspects (birds ingestion, TCMA, human mistake...), and to find a plausible single point of failure among the various subsystems involved. I was thinking of reversing the causality of the event, i.e. exploring a case where the engines would have behaved unexpectedly because of a major electrical failure, instead of the already explored case where both powerplants went AWOL first. Therefore, I have a couple questions for tdracer / fdr / other informed contributors (BTW, fantastic contribution guys, please keep the good info coming): 1. From the scarce info available, is it reasonable to conclude that the engines were totally shut down? Could they have just been set to idle or reduced thrust instead? 2. In the second case, if (and that's a big IF) a major electrical failure happened first (which could have triggered RAT deployment), and considering this plane is a FBW aircraft, could there exist a case where the FADECs would command idle thrust -- or significant thrust reduction -- because they receive invalid input data from the throttle controls? Kind of a garbage in-garbage out case? The associated scenario would be: major electrical fault (with subsequent RAT deployment) -> major protocol disturbance on ARINC/AFDX buses -> FADECs detect invalid data from the controls -> FADECS enter some kinf of safe mode and command reduced or idle thrust. Does it make sense or is it pure fantasy? 3 users liked this post. |
EDML
2025-06-17T10:13:00 permalink Post: 11904168 |
Not an avionics specialist, but electronics / software engineer here, with extensive experience in hardware fault tracking, protocol monitoring and software debugging in embedded systems : mods, feel free to delete this post if I am completely out of track (and thank you for the huge amount of work you've done trying to keep this discussion clean).
After I have read the whole thread, I think most of the community agrees about a lack of engine thrust being the cause of the crash. Searching in that direction, I'm trying to "think out of the box", discarding the usual suspects (birds ingestion, TCMA, human mistake...), and to find a plausible single point of failure among the various subsystems involved. I was thinking of reversing the causality of the event, i.e. exploring a case where the engines would have behaved unexpectedly because of a major electrical failure, instead of the already explored case where both powerplants went AWOL first. Therefore, I have a couple questions for tdracer / fdr / other informed contributors (BTW, fantastic contribution guys, please keep the good info coming): 1. From the scarce info available, is it reasonable to conclude that the engines were totally shut down? Could they have just been set to idle or reduced thrust instead? 2. In the second case, if (and that's a big IF) a major electrical failure happened first (which could have triggered RAT deployment), and considering this plane is a FBW aircraft, could there exist a case where the FADECs would command idle thrust -- or significant thrust reduction -- because they receive invalid input data from the throttle controls? Kind of a garbage in-garbage out case? The associated scenario would be: major electrical fault (with subsequent RAT deployment) -> major protocol disturbance on ARINC/AFDX buses -> FADECs detect invalid data from the controls -> FADECS enter some kinf of safe mode and command reduced or idle thrust. Does it make sense or is it pure fantasy? 1 user liked this post. |
Timmy Tomkins
2025-06-17T17:18:00 permalink Post: 11904486 |
Without breaching confidentiality, I am seriously considering major electrical issue, which rolled back both engines. It would fit the flight profile.
3 users liked this post. |
Xeptu
2025-06-18T04:28:00 permalink Post: 11904891 |
Thankyou I didn't know that and I'm not questioning you. I guess it doesn't matter electrically driven or engine driven, they cannot share the same power supply the gear must be retracted within 12 seconds. this in my opinion improves the argument for total electrical failure. Unless of course gear up was never selected..There must also have been a substantial loss of thrust on at least one engine.
|
meleagertoo
2025-06-18T09:08:00 permalink Post: 11905041 |
I am becoming somewhat suspicious about the supply of some of the info on this event. Firstly, the data recorders have been in the hands of the authorities for many days now and must surely have revealed something significant, either good data on the initial cause or, perhaps, in the case of a major electrical failure, nothing much. Either way we've heard nothing.
Equally despite the even longer timescale casualties remain at a quoted 270 odd which seems to me likely highly inconsistent with the location of the accident. Only 30ish casualties on the ground? Is this likely, given the number of burned-out buildings we've seen (and I get the impression we've also not been shown the true extent of the devastation.) My impression is that the authorities know much more than they are saying and are witholding it which suggests to me that there are aspects of 'saving face' perhaps in a reluctance to admit what happened, which implies the truth - of both initial cause and casualty numbers - may be uncomfortable politically. 2 users liked this post. |
oliver2002
2025-06-18T09:27:00 permalink Post: 11905057 |
I am becoming somewhat suspicious about the supply of some of the info on this event. Firstly, the data recorders have been in the hands of the authorities for many days now and must surely have revealed something significant, either good data on the initial cause or, perhaps, in the case of a major electrical failure, nothing much. Either way we've heard nothing.
Equally despite the even longer timescale casualties remain at a quoted 270 odd which seems to me likely highly inconsistent with the location of the accident. Only 30ish casualties on the ground? Is this likely, given the number of burned-out buildings we've seen (and I get the impression we've also not been shown the true extent of the devastation.)
My impression is that the authorities know much more than they are saying and are witholding it which suggests to me that there are aspects of 'saving face' perhaps in a reluctance to admit what happened, which implies the truth - of both initial cause and casualty numbers - may be uncomfortable politically.
![]() 14 users liked this post. |
sorvad
2025-06-18T17:17:00 permalink Post: 11905409 |
Water was mentioned earlier in the previous iteration of this thread, as I recall by one of the most well respected contributors on the forum and an expert in flight testing and certification issues. There have been a couple of well known incidents of flight deck screens going blank due to all sorts of electrical problems caused by water ingress into the E&E bay, fortunately in daytime vmc and not on particularly electric jets, and both I believe at rotation. The one I recall had it’s L1 door left open during a black rainstorm in Hong Kong. It’s also been said that total electrical failure can’t result in in a double engine failure on the 787, but I wonder what multiple sequelae could result from such water contamination with an aeroplane that relies so much on electrical power and software? Another very remote probability but many accidents and incidents are. I don’t even know if there was any inclement weather before this flight, maybe someone could confirm?
4 users liked this post. |
sorvad
2025-06-18T17:35:00 permalink Post: 11905416 |
Water was mentioned earlier in the previous iteration of this thread, as I recall by one of the most well respected contributors on the forum and an expert in flight testing and certification issues. There have been a couple of well known incidents of flight deck screens going blank due to all sorts of electrical problems caused by water ingress into the E&E bay, fortunately in daytime vmc and not on particularly electric jets, and both I believe at rotation. The one I recall had it’s L1 door left open during a black rainstorm in Hong Kong. It’s also been said that total electrical failure can’t result in in a double engine failure on the 787, but I wonder what multiple sequelae could result from such water contamination with an aeroplane that relies so much on electrical power and software? Another very remote probability but many accidents and incidents are. I don’t even know if there was any inclement weather before this flight, maybe someone could confirm?
1 user liked this post. |
FlightsofFancy
2025-06-19T04:23:00 permalink Post: 11905710 |
More holes in the Swiss Cheese?
Early during the 787 flight testing phase (9 Nov 2010) before the battery fire escapades, there was an electrical fire aboard aircraft ZA002 that had potential for serious consequences.
From memory, the 787 electrical distribution does not involve electro-mechanical contactors but instead uses solid state devices that are controlled by software. The Air India accident aircraft was experiencing electrical problems in the cabin on the prior flight according to passenger reports. Were these problems addressed or where they non-MEL items? The accident aircraft seems to have experienced a significant electrical event coincident with transition from Ground to Air mode (which I would expect results in some software reconfiguration of the aircraft electrical system). If the ground to air transition momentarily activated a grounded electrical system, then there could be a rather large plasma cloud of vaporized metal surrounding adjacent wires which could send electrical power to places it would not normally go. Swiss Cheese model anyone? \x93An aircraft can be in service for many years before supposedly 'random' failures are discovered. We had a 747-400 departing JNB many years ago, and during the take off roll, the inboard leading edge flaps (flaps on the Jumbo, not slats) retracted. The only indication of this was the flaps secondary display popping up and crosses appearing over the inboard LE flaps. No Master Caution, no warnings of any kind. Apparently the system was working exactly as 'designed\x92! During the landing roll, when Reverse is selected, the inboard LE flaps automatically retract, to avoid damage from any debris blown up by the effect of the reverse thrust. In this take off scenario, due to maintenance work being carried out earlier in the day, the aircraft thought the reversers had been selected, and 'correctly' retracted the flaps. At rotation, the stick shaker activated, and the aircraft struggled to get airborne. The passengers got lucky, as the First Officer, who was Pilot Handling, was an experienced aerobatic pilot, and was able to keep the aircraft airborne, flying in heavy buffet and with the stick shaker activated until the air-ground logic finally caught up after gear retraction, and the LE flaps deployed again. Not something that most regular guys would cope with, particularly at night, with no outside horizon for reference. Pilots who\x92ve operated around Africa will know what I'm talking about. They dumped fuel and returned to JNB. This happened on May 11th 2009 (Google it) - just how long had the Jumbo, of all variants, been in service before this 'glitch' was discovered? The actual issue was that during the earlier maintenance, the engineers had cycled the thrust levers, with the engines off, all the way through the reverse gates, and back again (the aircraft had arrived earlier that day, and a reverser had failed to deploy). What no one knew, was that the action of moving the thrust levers through the reverse gate, would latch a bit of software logic in one of the computers on board, causing a near catastrophic sequence of events. We all know and love the Jim Reason Swiss cheese model - I suspect we're going to discover some previously unknown holes.\x94 I find it rather a coincidence that this aircraft had so many electrical problems, had, not been retrofitted to solve one electrical issues like all 787s in the US had, and suffered what appears to be some kind of electrical failure. 12 users liked this post. |
Aerospace101
2025-06-19T14:11:00 permalink Post: 11906054 |
It does not follow that MCAS malfunction is a software malfunction.
As far as I know, the software functioned exactly as it was specified/required to function. The problem did not lie in the quality of the software, as you suggest. It lay in the functional requirements for the function, and the hazard analysis of those requirements, and those are manufacturer tasks. In a total electrical failure, when the system switches to emergency battery power, how are input variables like rad alt and wow switches processed? (these were inputs someone mentioned on the 747-8, have the TCMA inputs been identified yet?) I speculate the gear truck forward tilt is a symptom of a C hydraulic failure caused by a total electrical failure around the time of VR. Once they got 10 deg nose up on the rotation, with a total electrical failure, could the FADEC receive erroneous rad alt or wow inputs, and how would TCMA handle these inputs in the transition from ground to air logic? What is baffling is the simultaneous nature of the suspected dual engine shutdown. There is no obvious asymmetry, with the flight path or rudder movements. If the engine fuel control switches had been manually cut one at a time, there should have been some visible flightpath change or flight control response. Something happened to both engines at exactly the same time. 2 users liked this post. |
jdaley
2025-06-19T20:35:00 permalink Post: 11906349 |
slf/ppl here - with a respectable amount of experience in software delivery for real-time/embedded/safety critical systems. Software development in this area really is an engineering discipline and bears no resemblance to common practice in other areas. Couple that with the requirements for function duplication/triplication, harness separation et al then IMHO the chances of FADEC etc software errors are effectively zero.
I'm commenting to make that point but also to link the videos and the FR-24 dataset - (below with my deltas for height/time added) ![]() Extract from FR24 csv dataset As noted in both threads to date everything was normal until it wasn't - the two values for fpm above are subject to FR24 variance of +/- 25' so even these suggest a normal climb at this stage of flight ca 2,000fpm. FR24 Lat/Longs all follow the centre line. On this data the climb stops at around 70' AGL and electrical failure around 2s later. Again, as noted in the threads, this aligns with when gear up might have been expected. If the climb stopped because of fuel shutoff then 2s for spool down to electrical failure isn't out of the question. Looking at the two videos. The CCTV video indicates a total flight time, from rotation, of about 32s, subjectively levelling off ~14s after rotation. The rooftop video has a flight time ~14s suggesting the video starts ~18s after rotation. The rooftop video evidences the RAT as deployed from the beginning - meaning it must have been deployed by at least 16s after rotation - which aligns with the ADS-B indicated electrical failure. If the forward flight recorder really is being sent to the US for recovery then it's reasonable to assume that the rear recorder contains nothing after the electrical failure and they are hoping the forward recorder captured something from the cockpit in the final 16s. I don't have any experience of flight deck CRM but I don't see how those timings allow problem identification/misidentification and subsequent action - ie it wasn't down to the crew. However: The maximum aircraft height in the CCTV video, as judged by wingspan, appears higher than 71' - though it is certainly less than a wingspan height at the beginning of the rooftop video. I haven't seen, in the threads, any statement of what happens on the flight deck with a total electrical failure - is it a 4s blackout whilst the RAT deploys and systems restart? - or are there batteries that keep something alive? 3 users liked this post. |
user989
2025-06-19T23:26:00 permalink Post: 11906480 |
Summary of main theories
DISCLAIMER: Poster (a) is one of the (apparently quite numerous) lawyers following this thread; (b) a long-time forum lurker and aviation enthusiast who loves studying FCOMs for fun (to each his own, I guess); (c) has followed and read this thread from the start.
What I cannot do is add new theories or uncover any new facts the actual experts have not already thought of. However, since summarizing and structuring information is one thing lawyers tend to regularly do (and sometimes even do well), here is my attempt at a useful contribution to this thread: an attempt to summarize the main theories discussed here since day one (which I think hasn't been done for quite some time) in the hope that a birds-eye view will be helpful to those who have not read everything since the beginning or might even trigger some new flash of inspiration for someone more knowledgable than me. I have focused on the cons since there does not seem to be enough evidence to come to any positive conclusion. I shall try to be concise and to refrain from personal evaluations of my own. Of course, no disrespect whatsoever is intended towards all those who have contributed to this thread and to the individual theories, one or combinations of which may turn out to have led to this tragic outcome. That arguments can be made against every single theory that has been propagated seems to be the result of the highly improbable and unusual nature of this deplorable event and certainly not due to any lack of knowledge or reasoning skills in this forum. DEAR MODS: If I have distorted anything or if, meaning well, should have achieved the opposite \x96 I guess you know where the delete button is\x85 Anyway, here goes: A. Misconfiguration or wrong takeoff data Widely refuted, since
Still brought up from time to time. However, widely disregarded due to
It should be pointed out that the question of "RAT in or out" was for a while the most contentious in this thread. C. Low-altitude capture Still argued, even if refuted by many since
Various possible reasons for this have been discussed: I. Bird strike/FOD
1. Loss of electric fuel pumps
Suction feed would have provided sufficient fuel pressure.
2. Fuel contamination
No other aircraft affected, no measures taken at airport. Simultaneous flameout due to contaminated fuel very unlikely.
3. Vapour lock
Unlikely to occur in this scenario. Even if (momentarily) no sufficient fuel pressure from the center tank, the engines would have been fed by the wing tanks.
III. Improper maintenance
Unclear which maintenance measures could possibly have been performed that would have resulted in simultaneous loss of both engines. No apparent relationships between malfunctions reported by previous passengers and essential systems. IV. Large-scale electrical fault (e.g. due to water in E&E bay) The engines will continue to run if electrical power is lost. FADECs are powered independently. V. Shutdown of engines by TCMA A parallel is drawn to the ANA incident. However, this would require not only a fault in the air/ground logic but also a sensed discrepancy between T/L position (not necessarily idle) and thrust output on both engines simultaneously. VI. (Inadvertent) shutdown by flight crew
1. Spontaneous execution of memory items (fuel control switches OFF, then ON; deploy RAT) due to assumed engine malfunction
In contrast to mistakenly shutting down the wrong engine after having correctly diagnosed the problem as per SOP, this would require not only a simple error in execution but a counter-intuitive unilateral action immediately after takeoff against basic principles of SOP or CRM.
2. No indications whatsoever of an intentional shutdown for nefarious reasons
(Would also be inconsistent with the content of the alleged mayday call.)
VII.
Malfunction/mishandling of the fuel cutoff switches (most recent)
1.
Wear or improper operation of the switches, so that they do not lock but can shift back into the OFF position.
Argued to be impossible due to robust switch design, preventing switch release in any other than a locked position.
Actuation of the switches by an item placed before them which was pushed onto the switches by retarding thrust levers seems equally unlikely due to force required to pull the switches out of the locked position.
2.
Spilled drink leading to short in the wiring
Hardly conceivable that before takeoff open liquid containers would be placed anywhere where they could spill onto the pedestal.
29 users liked this post. |