July 12, 2025, 21:55:00 GMT
permalink Post: 11920870
A query, the FO was pilot flying and the Captain was pilot monitoring. Is it SOP that pilot flying sits in the LHS at takeoff? As I understand it the situation on power failure is that the battery backup will keep the displays alive until the APU comes online but only on the LHS. Trying to maintain best gliding performance and look for best landing site without any instruments to show speed or attitude would be more difficult. Captain taking over and swapping roles at 200 feet mid crisis is disruptive.
Tdracer has certainly explained that separation of cabling runs etc would have it very improbable that a single cable fault or short would impact both engines simultaneously in the same way. The CVR data is derived from local sensors with a dedicated battery backup, however all the FDR data and the fuel shut off commands are electrical signals which ultimately have a common source in the aircraft power buses. A water ingress into the EE bay at rotate which momentarily shorted all the low voltage buses to higher AC voltage is unlikely but is it unlikely to the same extent.
July 13, 2025, 10:57:00 GMT
permalink Post: 11921226
Black swan event
Many years ago I was a F/O flying with a very experienced Captain in northern Canada. The day consisted of 7 legs, most of which were 30 minutes or less. We left Yellowknife for Hay River, which takes about 20 minutes. I was flying and while on descent something very strange occured. Through 5000 feet or so I noticed the Captain doing something with the electrics. (If I remember correctly you can't put both main electrical busses on the APU while in flight on the 737-200). The Captain was trying to put, first one and then the other main bus on the APU. When he couldn't he would return to normal in flight configuration and then make another attempt. I asked him what he was doing. At this point he stopped and stared at the electrical panel and then at me. He then said "oh my god, I thought we were on the ground!"
He was very competent and had done these flights a million times. But something was distracting him that day to the extent that he actually thought we were 10 minutes or so further along in the day than we were. No harm done in our case but when I first heard about the preliminary findings I was immediately reminded of that day.
He was very competent and had done these flights a million times. But something was distracting him that day to the extent that he actually thought we were 10 minutes or so further along in the day than we were. No harm done in our case but when I first heard about the preliminary findings I was immediately reminded of that day.
July 13, 2025, 13:29:00 GMT
permalink Post: 11921325
This is excellent, thank you. It has helped me to crystallise a thought about the length of time the switches were at cut off.
10 seconds is a long time in a life threatening situation (like most clich\xe9s, the cinematic trope of time slowing down only reflects people's real experiences, mine included). Reaction times to completely unexpected events can be in the order of 3-5 seconds, but I find it hard to think that it would have taken any pilot as much as 5-7 seconds to set the first switch back to run. It's not something that anyone trying to save the aircraft is going to take time to consider.
Possible explanations for the length of time are a physical altercation - but if that was so, then why did the switches then stay at run? We will be none the wiser on that, at least until the next report. Another, perhaps more likely possibility is that the switch movement itself was unnoticed by at least one of the pilots, and was not noticed until its effects took hold a couple of seconds later (my phrasing here is intended to leave open the question of how the switch moved, or was moved). Combined with the startle reaction time, this would start to explain a 10 second delay. So I expect the CVR comments are towards the later end of the possible range indicated in the excellent diagram.
10 seconds is a long time in a life threatening situation (like most clich\xe9s, the cinematic trope of time slowing down only reflects people's real experiences, mine included). Reaction times to completely unexpected events can be in the order of 3-5 seconds, but I find it hard to think that it would have taken any pilot as much as 5-7 seconds to set the first switch back to run. It's not something that anyone trying to save the aircraft is going to take time to consider.
Possible explanations for the length of time are a physical altercation - but if that was so, then why did the switches then stay at run? We will be none the wiser on that, at least until the next report. Another, perhaps more likely possibility is that the switch movement itself was unnoticed by at least one of the pilots, and was not noticed until its effects took hold a couple of seconds later (my phrasing here is intended to leave open the question of how the switch moved, or was moved). Combined with the startle reaction time, this would start to explain a 10 second delay. So I expect the CVR comments are towards the later end of the possible range indicated in the excellent diagram.
If powered by the RAT or APU would that introduce a time delay before you an can effectively put them back to Run?
July 13, 2025, 18:03:00 GMT
permalink Post: 11921493
Electrical effects of engine rollback
As I understand it from previous discussions, without the APU, all electrical power except for that DC power provided by battery to essential systems would have been lost.
With the copilot as PF, would he have lost his instrument displays? If so, possibly additional startle effect and workload for him.
Why did the ADS-B information keep going on for so long? My understanding from previous threads was that loss of ADS-B was considered an indication of loss of electrical power.
What else would be expected with loss of power?
Some general speculation: I find it hard to understand the long delay from what must have been the onset of obvious issues to the time the first engine is set to "RUN". I wonder if much more cockpit dialog intervened, e.g. PF requesting PM to turn the fuel switches back on (since he had his hands full), and eventually operating the switches himself, with the delay and time gap between the two switches being turned to "RUN" being attributable to being preoccupied with flying the aircraft under trying conditions.
July 13, 2025, 18:39:00 GMT
permalink Post: 11921522
I would like to raise a subject that I don't believe has been discussed here since the Preliminary Report was published, namely what happened to the aircraft's electrical systems as a consequence of the dual engine rollback and thereafter (RAT deployment, partial engine recovery, etc.). Apologies if I've missed posts on this topic here, but I have tried to review all of this thread quickly after previously reading most of it in detail.
As I understand it from previous discussions, without the APU, all electrical power except for that DC power provided by battery to essential systems would have been lost.
With the copilot as PF, would he have lost his instrument displays? If so, possibly additional startle effect and workload for him.
Why did the ADS-B information keep going on for so long? My understanding from previous threads was that loss of ADS-B was considered an indication of loss of electrical power.
What else would be expected with loss of power?
Some general speculation: I find it hard to understand the long delay from what must have been the onset of obvious issues to the time the first engine is set to "RUN". I wonder if much more cockpit dialog intervened, e.g. PF requesting PM to turn the fuel switches back on (since he had his hands full), and eventually operating the switches himself, with the delay and time gap between the two switches being turned to "RUN" being attributable to being preoccupied with flying the aircraft under trying conditions.
As I understand it from previous discussions, without the APU, all electrical power except for that DC power provided by battery to essential systems would have been lost.
With the copilot as PF, would he have lost his instrument displays? If so, possibly additional startle effect and workload for him.
Why did the ADS-B information keep going on for so long? My understanding from previous threads was that loss of ADS-B was considered an indication of loss of electrical power.
What else would be expected with loss of power?
Some general speculation: I find it hard to understand the long delay from what must have been the onset of obvious issues to the time the first engine is set to "RUN". I wonder if much more cockpit dialog intervened, e.g. PF requesting PM to turn the fuel switches back on (since he had his hands full), and eventually operating the switches himself, with the delay and time gap between the two switches being turned to "RUN" being attributable to being preoccupied with flying the aircraft under trying conditions.
There seems to be a period around second 12/13 post V1 where engines are (or should) be likely below idle, but prior to RAT power generation.
Note that the report explicitly states the RAT started providing hydraulic power 5 seconds after engine shutdown commenced. It doesn't reference electrical power. So we don't know whether this was at the same time - others may clarify re: RAT operation.
But either way, it would appear there would be a gap in power (which, incidentally, would tie in with the survivor commentary). But yet ADS data continued.
If in fact there was a momentary loss of power then that would contribute heavily to the startle and "delay" in refiring (although comments here make me think there wasn't really such a delay anyway).
(And incidentally would make what appears to be a really rather valiant attempt to save the aircraft even more impressive)
July 13, 2025, 19:06:00 GMT
permalink Post: 11921541
These for me are very interesting questions.
There seems to be a period around second 12/13 post V1 where engines are (or should) be likely below idle, but prior to RAT power generation.
Note that the report explicitly states the RAT started providing hydraulic power 5 seconds after engine shutdown commenced. It doesn't reference electrical power. So we don't know whether this was at the same time - others may clarify re: RAT operation.
There seems to be a period around second 12/13 post V1 where engines are (or should) be likely below idle, but prior to RAT power generation.
Note that the report explicitly states the RAT started providing hydraulic power 5 seconds after engine shutdown commenced. It doesn't reference electrical power. So we don't know whether this was at the same time - others may clarify re: RAT operation.
If memory serves me right on the 777 the electrical output capacity of the APU is about 8-10 times the output capacity of the RAT.
It will likely be even more on the 787.
July 13, 2025, 19:10:00 GMT
permalink Post: 11921547
I assume this means that the APU was not operational until this point?
July 13, 2025, 19:16:00 GMT
permalink Post: 11921552
I don\x92t know if it started to open or was registered open at 8 seconds.
July 13, 2025, 19:18:00 GMT
permalink Post: 11921555
The APU needs air to operate. The inlet provides that air.
July 13, 2025, 19:20:00 GMT
permalink Post: 11921557
I believe the APU can take quite a while to start, certainly more than 30 seconds. The APU inlet door in the wreckage is open but it's not clear if it is fully open or perhaps closed a little with the loss of whatever power is used to drive the actuator. Electrical or hydraulic? I have seen other 787 APU inlet door photos showing what seems to be a wider aperture but that was on an aircraft on the ground.
July 13, 2025, 19:27:00 GMT
permalink Post: 11921563
So this brings me back to my original observation (and that of another poster) - it would appear that there was a time period of at least 2 seconds, and potentially longer depending upon RAT electrical power, where the aircraft lost some (?) or all (?) electrical power, which hasn't really been discussed.
This would definitely contribute to recovery challenges (albeit slightly tangential to root cause discussion).
(And, strangely, ADS data appeared to continue during the period this would have occurred)
July 13, 2025, 19:29:00 GMT
permalink Post: 11921564
Yes.
The ADS-B data collected by FR24 leave the aircraft at 172 knots
8 seconds
4 seconds into the outage. Vr was 155 knots per the report. The preliminary report also says it crashed at 8⁰ nose-up attitude, which was after the "flare".
Please tell me how recoverable that is, with hypothetical 95% thrust on both engines
2
6 seconds later.
edit: reviewed fr24 data and adjusted time covered; I think it did decelerate to approximately 155 knots in 10 seconds, based on -3knots/second.
The ADS-B data collected by FR24 leave the aircraft at 172 knots
Please tell me how recoverable that is, with hypothetical 95% thrust on both engines
edit: reviewed fr24 data and adjusted time covered; I think it did decelerate to approximately 155 knots in 10 seconds, based on -3knots/second.
Beware of comparing the speeds from ADS-B, which are groundspeeds, with those from the report, which are IAS.
July 13, 2025, 19:37:00 GMT
permalink Post: 11921569
Thanks to you both.
So this brings me back to my original observation (and that of another poster) - it would appear that there was a time period of at least 2 seconds, and potentially longer depending upon RAT electrical power, where the aircraft lost some (?) or all (?) electrical power, which hasn't really been discussed.
This would definitely contribute to recovery challenges (albeit slightly tangential to root cause discussion).
(And, strangely, ADS data appeared to continue during the period this would have occurred)
So this brings me back to my original observation (and that of another poster) - it would appear that there was a time period of at least 2 seconds, and potentially longer depending upon RAT electrical power, where the aircraft lost some (?) or all (?) electrical power, which hasn't really been discussed.
This would definitely contribute to recovery challenges (albeit slightly tangential to root cause discussion).
(And, strangely, ADS data appeared to continue during the period this would have occurred)
Without the APU, would there have been sufficient power to restart even one engine, never mind two?
Could this be why the delay between the first and second switches being moved to RUN?
Does it also mean that in reality the 10 seconds between OFF and RUN is immaterial as there was insufficient electrical power to start the engines anyway?
July 13, 2025, 19:56:00 GMT
permalink Post: 11921587
Not sure how much more evidence you need to start a discussion.
We as operators are trying to put ourselves in that situation and describe likely outcomes based on present experiences. The most likely event is the PM orchestrating this, the Captain in this case. This however is up for debate\x85 the debate we should be having\x85 not APU doors.
July 13, 2025, 20:21:00 GMT
permalink Post: 11921608
Some human in that flight deck moved both fuel switches to cutoff, physically moved them, one after the other. Another human, possibly either human in that flight deck then questioned verbally why they did that. This is factual and proven evidence as per the official report. Why are we not focusing on the who and why!?
Not sure how much more evidence you need to start a discussion.
We as operators are trying to put ourselves in that situation and describe likely outcomes based on present experiences. The most likely event is the PM orchestrating this, the Captain in this case. This however is up for debate\x85 the debate we should be having\x85 not APU doors.
Not sure how much more evidence you need to start a discussion.
We as operators are trying to put ourselves in that situation and describe likely outcomes based on present experiences. The most likely event is the PM orchestrating this, the Captain in this case. This however is up for debate\x85 the debate we should be having\x85 not APU doors.
I certainly don't need more evidence than we have for discussion. I just think a lot more evidence is necessary to conclude that either crew member on that flight deliberately killed the engines intending to crash the jet and, for some reason, accused the other of doing so. Indeed, I don't think we have any actual evidence for that. We simply have a set of circumstances that make that one of only a few possibilities we can reasonably imagine. Discussing it as a possibility is reasonable (although I don't think we can get anywhere on that path without evidence), but claiming that possibility as the one, the truth, what really happened, is not reasonable, not justified by the available evidence. And making unjustified claims that amount to accusing a pilot of mass murder, in a forum that citizens and journalists from around the world always turn to for information in the wake of a major airliner crash, seems like a very bad idea to me.
July 13, 2025, 20:27:00 GMT
permalink Post: 11921615
I don't remember joining a debate about the APU door. In fact, I haven't seen such a debate, although I have seen some questions and speculation. I didn't read those posts carefully, but I got the sense that they were in the context of speculation about the possibilities for engine restart and thrust recovery, not about possible causal factors. Maybe I got that wrong.
July 13, 2025, 20:29:00 GMT
permalink Post: 11921621
July 13, 2025, 20:36:00 GMT
permalink Post: 11921626
From the point that the fuel cutoffs were switched back to run, the primary (perhaps only) relevant issues were time and altitude. The left engine was relit and recovering on it's own but the right would probably have needed cranking as it appears to have had a hung start because it was spooled down too far and the airspeed was too low. However, I'm pretty sure that even if the APU had already been running at takeoff, they still would have needed at least another 30 seconds if not longer for full thrust. Also, there was nowhere near enough time for the APU to start and come online here.
Last edited by Mrshed; 13th July 2025 at 20:49 .
July 13, 2025, 20:43:00 GMT
permalink Post: 11921632
Incidentally, the APU door started opening *after* the initiation of relight of the first engine.
Without the APU, would there have been sufficient power to restart even one engine, never mind two?
Could this be why the delay between the first and second switches being moved to RUN?
Does it also mean that in reality the 10 seconds between OFF and RUN is immaterial as there was insufficient electrical power to start the engines anyway?
Without the APU, would there have been sufficient power to restart even one engine, never mind two?
Could this be why the delay between the first and second switches being moved to RUN?
Does it also mean that in reality the 10 seconds between OFF and RUN is immaterial as there was insufficient electrical power to start the engines anyway?
Normal start uses a lot of electrical power to drive the two starters. In a situation with only the RAT supplying electrical power there won't be anywhere near enough power to turn even one starter. Restart relies on windmilling only. Igniters don't need a huge amount of power, fuel will be gravity fed to the engine driven pumps. The APU autostart function will use power from the dedicated APU battery only.
Edit to add, it can take an age for the APU to start off the battery. Well over a minute.
July 13, 2025, 20:47:00 GMT
permalink Post: 11921636
I think there is a bit of confusion running in this thread about how the auto restart function works.
Normal start uses a lot of electrical power to drive the two starters. In a situation with only the RAT supplying electrical power there won't be anywhere near enough power to turn even one starter. Restart relies on windmilling only. Igniters don't need a huge amount of power, fuel will be gravity fed to the engine driven pumps. The APU autostart function will use power from the dedicated APU battery only.
Normal start uses a lot of electrical power to drive the two starters. In a situation with only the RAT supplying electrical power there won't be anywhere near enough power to turn even one starter. Restart relies on windmilling only. Igniters don't need a huge amount of power, fuel will be gravity fed to the engine driven pumps. The APU autostart function will use power from the dedicated APU battery only.