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Nick H.
2025-06-18T21:30:00 permalink Post: 11905563 |
@syseng68k
Consensus here is, that both engines where stopped by a closing fuel cut off valve, wich yields a fast loss of N2. The generators then shut down very quick as does the thrust in a few seconds. This is supported by the quick RAT extension which allowed the crew to control the flight. The APU did autostart too. A thrust changed with the thrust leaver to idle is much slower and would not result in the dramatic change in performance. Thrust set to idle will not engage the RAT since the electric generators would still work. So a thrust leaver changed to idle or any intervention by Autothrust (AT) would not yield to the RAT extension. Something or someone activated a fuel cut off. How and why that happened is the big question, the investigators have to answer. ![]() |
777ret
2025-06-18T22:38:00 permalink Post: 11905597 |
@syseng68k
Consensus here is, that both engines where stopped by a closing fuel cut off valve, wich yields a fast loss of N2. The generators then shut down very quick as does the thrust in a few seconds. This is supported by the quick RAT extension which allowed the crew to control the flight. The APU did autostart too. A thrust changed with the thrust leaver to idle is much slower and would not result in the dramatic change in performance. Thrust set to idle will not engage the RAT since the electric generators would still work. So a thrust leaver changed to idle or any intervention by Autothrust (AT) would not yield to the RAT extension. Something or someone activated a fuel cut off. How and why that happened is the big question, the investigators have to answer. 3 users liked this post. |
ignorantAndroid
2025-06-19T21:51:00 permalink Post: 11906415 |
No, very unlikely the pilots lost all control. In a total power failure (hydraulics and electrics) the pilots can control roll (by a specific spoiler pair) and pitch through the stabiliser. All electrically powered through wiring direct to control column.
It's possible the RAT was not providing correct power in the last moments, remember RAT provides Hydraulic (C system flight controls only) and Electrics. The evidence is the spoiler pair deflection behind the engines prior to impact. That specific spoiler pairing is only controlled by electrical power (directly connected to pilot control column). We should see other flight control deflections if the RAT was powering hydraulics. In the final moments I would speculate the flight controls had only emergency electric power from the battery. The direct wiring you're referring to is intended to provide minimal control in case of a complete failure of all ACEs. It allows for control signals but does not provide power. 1 user liked this post. |
Sumpie75
2025-06-20T01:11:00 permalink Post: 11906519 |
This incident is very perplexing to me. This is my first post on here and I am not a pilot. I have over a decade of experience in the RAAF as an engine fitter on Mirage and Hornet aircraft. Albeit a bit of time ago.
I have watched the video's and looked at the FR-24 data a hundred times. To me it looks like a normal rotation and at WoW everything starts to go wrong. Airspeed starts dropping off immediately going by the FR-24 data. If reports are correct the pilot makes his Mayday call. FR-24 data stops. In the video from the balcony I agree the RAT is out and operating but I can also hear the engines at idle or just above (maybe flight idle). If the captain manually deployed the RAT this makes sense to me. In both video's I don't see any aircraft behavior that would suggest they are not flying the aircraft. Is there an electrical fault at WoW that renders the cockpit dark and therefore manually deploying the RAT (possibly initiating APU start, inlet door is open at crash site) would make sense to restore cockpit power. I can't understand any pilot shutting down both engines at 200ft AGL. He would surely know that his fight is over at that point. I am not ruling out pilot error (configuration or otherwise) but my hat goes off to two pilots that I believe were trying to fly this aircraft until it hit the ground. Sorry if my wording is a bit off but mine is military background not commercial. 4 users liked this post. |
Musician
2025-06-20T05:30:00 permalink Post: 11906603 |
TCMA things, imagination and evidence
You may be surprised to know that TCMA doesn't require that, it just requires a differential between commanded and actual thrust.
It has never triggered during takeoff until now. Maybe it still hasn't been. We'll see. Given there is an actual example of a 787 in the wild shutting down both of it's engines when it shouldn't (ANA), I'm surprised how complacent people are that this couldn't be the cause..Software can always have weird corner failures that could never have been thought of or tested. Note that the thrust lever actuators are wired to the FADECs, and that the TCMA gets the T/L position from that. For TCMA to trigger, it has to determine that its FADEC (on that engine) failed to achieve a commanded reduction in thrust. So we're either looking at a weird, unprecedented edge case, or a FADEC failure, or both.
Just so I have this clear, are you saying that the implementation of the TCMA functionality involved
no
new components being added to the pre-existing FADEC? Are you saying, in effect, that the two switch relays described in the TCMA patent application, which relays and their configuration achieves the described two channel redundancy, were already there as components or are mere depictions of what the software does itself?
Originally Posted by
Lead Balloon
I am not suggesting you are wrong and, as I've said before, the descriptions and schematic in the patent application are just 'big hands / small maps' concepts. However, if TCMA functionality "is simply a bit of software in the FADECs", merely sending a 1 or 0 or other signal into a point in the pre-existing FADEC that already had control over fuel cutoff (with the TCMA software merely monitoring data busses, rather than direct sensor outputs, to work out thrust lever position and whether or not the aircraft is 'on the ground' for TCMA purposes) I for one would really like to know that for sure and get my head around the implications.
With a MCAS crash, it required a hardware problem with an AOA sensor, used as input to a correctly working MCAS, to cause the aircraft to behave erratically. With a correctly working TCMA, I believe it'd require two hardware problems to get TCMA to shut down the engine, as there'd have to be an implausible thrust lever reading, and a FADEC/engine failure to process it within the TCMA allowed range ("contour"?). On both engines, separately and simultaneously. That leaves a software problem; it's not hard to imagine. The issue is, at this point it's just that: imagination. I could detail a possible software failure chain, but without examining the actual code, it's impossible to verify. We simply don't have the evidence. I could just as well imagine a microwave gun frying the electronics on both engines. An escaped hamster under the floor peeing on important contacts. A timed device installed by a psychopathic mechanic. There's no evidence for that, either. This process is a way to psychologically cope with the unexplained accident, but because it lacks evidence, it's not likely to identify the actual cause. We've run the evidence down to "most likely both engines failed or shut off close to rotation, and the cause for that is inside the aircraft". Since the take-off looked normal until that failure, we have no clues as to the cause hidden inside the aircraft. We need to rely on the official investigation to discover and analyse sufficient evidence. The post-crash fire is going to make that difficult. "Both engines failed or shut off close to rotation" explains all of the evidence : it explains an unremarkable take-off roll, loss of lift, absence of pronounced yaw, loss of electrical power, loss of the ADS-B transponder, RAT deployment, the noise of the RAT banging into place and revving up, emergency signs lighting up, a possible mayday call reporting loss of thrust/power/lift, and a physically plausible glide from a little over 200 ft AAL to the crash site It explains what we saw on the videos, what the witness reported, where the aircraft ended up, and the ensuing sudden catastrophe. I don't believe we have evidence for anything else right now—I'd be happily corrected on that. ----- Edit: the evidence of the crash photo with the open APU inlet door, and the main gear bogeys tilted forward, are also explained by the dual engine failure/shut off. Last edited by Musician; 21st Jun 2025 at 06:48 . Reason: more evidence 17 users liked this post. |
Aerospace101
2025-06-21T00:41:00 permalink Post: 11907411 |
10 users liked this post. |
MaybeItIs
2025-06-21T01:21:00 permalink Post: 11907432 |
For those postulating the RAT was not deployed, what counter explanations do you have for the following clues?
1 user liked this post. |
Sailvi767
2025-06-21T12:31:00 permalink Post: 11907707 |
It’s a possibility (as is virtually anything that doesn’t break the laws of physics) but all the training, practicing and checking would have been to emphasise SOPs, which are to leave all the engine controls where they are until you have done a proper interactive diagnosis at a safe height with the flightpath assured.
Where the meme has come from that jet pilots have to shut down engines as quickly as possible I don’t know but it is incorrect. If you left a failed engine without securing it for 5 minutes, little to no harm would come of it. Even if it was on fire (which is not necessarily flames, just higher than normal temperatures inside the nacelle) they are certified to be in this condition for some considerable time before it becomes a problem. Yes, I think the phrase “without undue delay” could be used for a fire indication but that’s a minimum of 400’AGL in Boeings and does not absolve you of all the cross-checking and CRM that should happen with an engine shutdown. This is practiced/checked at the least every 6 months in EASA land and any attempt to rush a shutdown at low level would lead to a debrief and more training/checking. To put it this way, control of the aeroplane and lateral/vertical navigation is far more important than doing stuff with a failed power plant. Something like an ET should be absolutely prioritised over engine drills. 14 users liked this post. |
TURIN
2025-06-21T15:12:00 permalink Post: 11907831 |
There are maintenance access doors directly belew the APU that open up like a Clamshell. There are other access doors nearby for example just forward of the APU firewall bulkhead there is an access door, this allows entry into the stabiliser bay rear section. There is another stab bay access door just forward of the horizontal stabiliser on the left side which allows access to the forward stabiliser area, screw jack, fin access and the rear pressure bulkhead. I don't think there are any others. 1 user liked this post. |
OPENDOOR
2025-06-22T15:40:00 permalink Post: 11908632 |
If it has no power it won't record anything at all, like the fact that multiple electrical systems are U/S but as a limited power supply from the RAT or APU comes on-line it would have something to record. It seems to me absurd that it is not powered at all times.
3 users liked this post. |
TURIN
2025-06-29T09:22:00 permalink Post: 11912902 |
Ask the Apollo astronauts? The ISS Crew members? But don't mention 9/11! The fireballs just don't compare.
It has been said that there are three stages of truth: ridicule, violent opposition and acceptance as self-evident. Obviously, we're not there yet ![]() Of course the aircrew needs a lav within their easy reach. I don't have a cross section or plan to work with (Google not obliging), but if you post, I'll take a look. Likely, I'd compartmentalize the lav with the EE Bay space immediately below, and install a "bilge tray and drain" below the lav space and above the EE Bay compartment. If it has to be used for EE Bay gear, I'd probably rack the 28V Batteries there, with the required fireproof casings and exhaust ports etc. (Also absurd, but true.) And I'd make sure the batteries themselves were fully protected by moulded plastic "hats", similar to what they use on the big 12V battery pairs on large trucks. I guess you could fit a couple of TRUs there as well, again, well-protected from dripping conductive liquids... And maybe, you could house [one of?] the EE Bay air conditioner unit It will come as no surprise to anyone that EE bays are well protected with the sort of things you have described. The 787 batteries are also in separate EE bays. Main one in the front and the dedicated APU battery in the power electrics bay aft of the landing gear. They are both contained in fireproof boxes that will vent to atmosphere in the event of a thermal runaway. I have been working on 787s for over a decade and leaks from gallies and lavs has not once been on my list of snags. 30 users liked this post. |
fdr
2025-06-30T03:37:00 permalink Post: 11913337 |
It will come as no surprise to anyone that EE bays are well protected with the sort of things you have described.
The 787 batteries are also in separate EE bays. Main one in the front and the dedicated APU battery in the power electrics bay aft of the landing gear. They are both contained in fireproof boxes that will vent to atmosphere in the event of a thermal runaway. I have been working on 787s for over a decade and leaks from gallies and lavs has not once been on my list of snags. When pax flush clothing and other rubbish down a vacuum toilet system, the potential for stuff to not work as advertised is not zero. 9 users liked this post. |
TURIN
2025-07-01T00:40:00 permalink Post: 11913970 |
I did look into this while analyzing the audio for RAT confirmation, but I did not conclude with anything other than that the engines where clearly not at any kind of take off power.
I did not find good enough material to compare to, and time was lacking a bit. There is engine noise, or engine-like noise from there, somewhat comparable to an engine at idle, that fades out into the background noise at the same rate as the RAT. I don\x92t know if it comes from an engine at idle, windmilling, an engine producing some power, or if it is even just aerodynamic noise from the rest of the airframe. I\x92ll give it another go if time allows. APU autostart? Not sure really, it takes several seconds for the inlet door to open. |
Someone Somewhere
2025-07-01T06:48:00 permalink Post: 11914048 |
Hold your horses there
Bloggs
, I didn't say they did, I said centre tanks were typically turned on at that altitude (using a certain 737 operator as a guide). As the check list that you posted shows the centre pumps will automatically turn off because of load shedding once an engine is started.
Once both engines are running and the four VFSGs are online, I would not expect any load shedding and certainly not of flight loads like fuel pumps. The Airbus manuals imply or clearly state that centre pumps are inhibited when the flaps are extended, so both engines draw from the wing/main tanks. I haven't seen anything clearly matching in the Boeing manuals. |
TURIN
2025-07-01T08:49:00 permalink Post: 11914118 |
In my experience the APU supplies enough power to run all systems. Hydraulic pumps, fuel pumps etc |
adfad
2025-07-01T09:32:00 permalink Post: 11914147 |
I know that the engine driven pumps have documented limitations and that the regulations allow for some limitations. I know that at least one of these limitation is high altitude and I _suspect_ that the design intends for this unlikely scenario (engine driven fuel pumps alone with no AC pumps) to guarantee enough fuel flow to get to an airport and land. I also suspect that the APU is expected to solve loss of all AC generators - and as we know, there wasn't enough time for it to start in this scenario. |
Someone Somewhere
2025-07-01T10:19:00 permalink Post: 11914164 |
Not really relevant to what you quoted though, as the scenario in question requires:
I also don't see any evidence that engine driven fuel pumps alone must be able to handle this scenario: provide enough fuel flow for takeoff and climb, even while the pitch is rotating, even in a hot environment with significant weight, even while the gear is stuck down.
I know that the engine driven pumps have documented limitations and that the regulations allow for some limitations. I know that at least one of these limitation is high altitude and I _suspect_ that the design intends for this unlikely scenario (engine driven fuel pumps alone with no AC pumps) to guarantee enough fuel flow to get to an airport and land. I also suspect that the APU is expected to solve loss of all AC generators - and as we know, there wasn't enough time for it to start in this scenario. The limitations at high altitude are primarily air/volatiles degassing out of the fuel. That's not going to be much of an issue at sea level, even if the engines are a bit higher up during rotation. APU is a nice-to-have; it's on the MEL. If you lose all four generators, it's because of some major carnage in the electrical software/hardware and chances of putting the APU on line even if it's operating are very slim. 1 user liked this post. |
Sailvi767
2025-07-01T12:39:00 permalink Post: 11914246 |
On the 767, 757 and A330 anytime you are in single generator operations the aircraft is load shedding. The 787 with a totally different electrical system might function differently.
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adfad
2025-07-01T12:55:00 permalink Post: 11914255 |
I believe that particular bug is fixed, though it's always possible there's other issues causing a total AC loss.
Not really relevant to what you quoted though, as the scenario in question requires:
The aircraft has two engines and should be able to climb out on one, plus it dropped like a rock . 'Significantly degraded' thrust isn't really compatible with what we saw. You'd also expect the engines to recover pretty quickly as it leveled off. The limitations at high altitude are primarily air/volatiles degassing out of the fuel. That's not going to be much of an issue at sea level, even if the engines are a bit higher up during rotation. APU is a nice-to-have; it's on the MEL. If you lose all four generators, it's because of some major carnage in the electrical software/hardware and chances of putting the APU on line even if it's operating are very slim.
I do agree that the engine driven pumps should be able to provide fuel alone, the whole point of these pumps is to keep the plane flying within some limitations, high altitude is one of those limitations, I propose that there may be others based on the following:
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Someone Somewhere
2025-07-01T13:08:00 permalink Post: 11914265 |
As an electronics and software engineer who has read the AD and related materials on the 248 day bug my understanding is that:
I do agree that the engine driven pumps
should
be able to provide fuel alone, the whole point of these pumps is to keep the plane flying within
some
limitations, high altitude is one of those limitations, I propose that there may be others based on the following:
Cavitating destroys pumps rapidly - someone upthread said replacing the fuel pump immediately is SOP if it has suction fed. Expect end of life in tens of hours rather than tens of thousands. Some aircraft have switched to using jet/venturi pumps powered by returned fuel, like the A220. The electric boost pumps there are mainly for redundancy and are shut down in cruise; only one in each wing tank. Some A320s replace the centre override pumps with venturi transfer pumps. |