July 13, 2025, 17:40:00 GMT
permalink Post: 11921477
Hi,
I have a couple of questions. Forgive me for being late into this thread if any of them is already discussed:
1) I just read this in a Boeing manual:
2) Looking at the incident timeline, one of the pilots takes corrective action to reswitch to RUN position 10 seconds after maximum air speed is reached and 5 seconds after RAT is deployed. Is this normal?
It's not clear however that whether their conversation is after or before the RAT is deployed.
(No visual or auditory cues in the cockpit for a critical fuel switch action? Not hearing the engines shutting down?)
3) The same pilot that turns on Engine 1's fuel switch, turns on Engine 2's switch 4 whole seconds later. Why not consecutively, right one after the other, just like they were turned off one second apart?
If only he had done so the second engine might have recovered in time as well.
4) This aircraft's TCM has been replaced in 2019 and 2023, not related to a fuel switch issue. And there had been no fuel switch defect reports since 2023. One begs to ask if there had been a fuel switch defect report back in 2023 and what was the nature of it?
Are TCM's replaced as a whole, including the switches, twice? If so, why wouldn't they install a TCM version at least in 2023 with redesigned switches (w/ enhanced locking mechanism) mentioned in the FAA SAIB? Have they installed old/used TCM's manufactured prior to 2018 SAIB?
Please note that the RH and LH GE engines of the aircraft were only installed in March 2025 and May 2025 respectively, but they were used and dating from 2013 and 2012. Is this normal for a 12 year old Boeing aircraft to change so many mission critical components?
Electronic parts somehow, but how durable are those GE engines?
Thanks,
C.A.
I have a couple of questions. Forgive me for being late into this thread if any of them is already discussed:
1) I just read this in a Boeing manual:
The fuel control switches send signals to open or close fuel valves to operate or shutdown the engines.
- They send signals to the remote data concentrators (RDC) and the spar valve start switch relays.
- The spar valve start switch relays use these signals to control the spar valve and the high pressure shut off valve (HPSOV) in the fuel metering unit (FMU).
- The RDCs send the signals to the common data network (CDN) and then to the electronic engine control (EEC) to operate the FMU fuel valves (FMV and HPSOV).
The fuel control switches have 2 positions:
- RUN
- CUTOFF.
You must pull the switch out of a detent to select a position.
There seems to be RDC's (remote data concentrators) and CDN (common data network) between those fuel switches and the fuel valves. Is there any possibility that there may have been an electronic control module or sensor fault to generate such a signal rather than mechanical switch movements?
- They send signals to the remote data concentrators (RDC) and the spar valve start switch relays.
- The spar valve start switch relays use these signals to control the spar valve and the high pressure shut off valve (HPSOV) in the fuel metering unit (FMU).
- The RDCs send the signals to the common data network (CDN) and then to the electronic engine control (EEC) to operate the FMU fuel valves (FMV and HPSOV).
The fuel control switches have 2 positions:
- RUN
- CUTOFF.
You must pull the switch out of a detent to select a position.
2) Looking at the incident timeline, one of the pilots takes corrective action to reswitch to RUN position 10 seconds after maximum air speed is reached and 5 seconds after RAT is deployed. Is this normal?
It's not clear however that whether their conversation is after or before the RAT is deployed.
(No visual or auditory cues in the cockpit for a critical fuel switch action? Not hearing the engines shutting down?)
3) The same pilot that turns on Engine 1's fuel switch, turns on Engine 2's switch 4 whole seconds later. Why not consecutively, right one after the other, just like they were turned off one second apart?
If only he had done so the second engine might have recovered in time as well.
4) This aircraft's TCM has been replaced in 2019 and 2023, not related to a fuel switch issue. And there had been no fuel switch defect reports since 2023. One begs to ask if there had been a fuel switch defect report back in 2023 and what was the nature of it?
Are TCM's replaced as a whole, including the switches, twice? If so, why wouldn't they install a TCM version at least in 2023 with redesigned switches (w/ enhanced locking mechanism) mentioned in the FAA SAIB? Have they installed old/used TCM's manufactured prior to 2018 SAIB?
Please note that the RH and LH GE engines of the aircraft were only installed in March 2025 and May 2025 respectively, but they were used and dating from 2013 and 2012. Is this normal for a 12 year old Boeing aircraft to change so many mission critical components?
Electronic parts somehow, but how durable are those GE engines?
Thanks,
C.A.
When reading any of the data when it comes out, pay some attention to the sampling rate of the data being provided, it is quite possible to make erroneous assumptions where that is not taken into consideration. The data buses used to get data from the aircraft system to the recorder, and the recorders themselves use sequential sentences, and varyious rates.
IMHO.
July 13, 2025, 17:54:00 GMT
permalink Post: 11921488
The event shows that it's really imperative to relight the engines as quickly as possible.
The preliminary report says it took about 5 seconds for the engines to spool down to idle. 14 CFR \xa7 33.73 - Power or thrust response requires a jet engine to reach 95% thrust from stabilized flight idle in not over 5 seconds. So with a sufficiently quick reaction, flipping the switches back after 5 seconds, they could've been back in business by the time they actually flipped the switches back.
So it's not "flip the switches 3 seconds after liftoff and you're unrecoverable"; to be unrecoverable, there must also be sufficient time for the engines to spool down enough.
Don't ask, "why did you cut the engines", flip them back on. Go for the E in PACE.
The preliminary report says it took about 5 seconds for the engines to spool down to idle. 14 CFR \xa7 33.73 - Power or thrust response requires a jet engine to reach 95% thrust from stabilized flight idle in not over 5 seconds. So with a sufficiently quick reaction, flipping the switches back after 5 seconds, they could've been back in business by the time they actually flipped the switches back.
So it's not "flip the switches 3 seconds after liftoff and you're unrecoverable"; to be unrecoverable, there must also be sufficient time for the engines to spool down enough.
Don't ask, "why did you cut the engines", flip them back on. Go for the E in PACE.
It's possible from the timeline in the report that this statement was made at the same time (or even after) they were moved back to RUN. The report is ambiguous on this unfortunately...!
Re: spool down to idle, that is interesting and passed me by - the report certainly does imply it took 5 seconds, which is at odds at an earlier post from (I believe) tdracer , who said this would take 1, maximum 2, seconds.
However when I read it again, it's again ambiguous - the 5 seconds is when the RAT started supplying power, but this isn't clear and unequivocal that engine went below idle at the same time in the wording, although definitely heavily implied.
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: 11921543
"This" apparently meaning that the Captain deliberately and with evil intent moved the FCS switches to CUTOFF and then accused the FO of doing it.
Of course we can't accept it as fact. There's no credible evidence indicating that it happened, much less dispositive evidence.
Of course we can't accept it as fact. There's no credible evidence indicating that it happened, much less dispositive evidence.
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, 19:50:00 GMT
permalink Post: 11921583
Is there? Is there evidence for the scenario that you have endorsed, that the Captain deliberately, intending to crash the airplane, moved the fuel control switches to CUTOFF and then accused the FO of doing that? What is that evidence?
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, 20:27:00 GMT
permalink Post: 11921617
Quote: Originally Posted by
Contact Approach
But there is evidence, pretty clear evidence!
The "evidence" might be available, but I disagree it is available to us. I assert the prelim report has been deliberately sanitised to prevent us (i.e. everybody outside the AAIB circle) being given enough 'evidence' to make certain conclusions.
You/others might not like it, some might say it is obvious (I say not), but I think it is carefully worded enough to imply what might have happened, but nothing is clear - intentionally.
But there is evidence, pretty clear evidence!
You/others might not like it, some might say it is obvious (I say not), but I think it is carefully worded enough to imply what might have happened, but nothing is clear - intentionally.
July 13, 2025, 20:42:00 GMT
permalink Post: 11921631
Action slips - further information
Non-pilot here.
For those interested in reading more about 'action slips', including performing one routine function in place of another, the following free-access article goes into more detail:
Wiley Online Library: Oops! I Did it Again: The Psychology of Everyday Action Slips
As other people have perspicaciously pointed out, assuming that it was the Pilot Monitoring that transitioned the Fuel Cut-Off Switches from RUN to CUTOFF, what action would they likely have been attempting to perform
at that stage of the flight
for an action slip to be a likely possibility?
Alternatively, given that the PM was used to operating simulators, what conditions could have prompted him to do a sequence that was familiar to him of resetting the simulator (including operating the FCS switches), doing things that are inadvisable in a real aircraft?
If these are stupid questions, I apologise for taking up a mod's time processing the comment deletion.
For those interested in reading more about 'action slips', including performing one routine function in place of another, the following free-access article goes into more detail:
Wiley Online Library: Oops! I Did it Again: The Psychology of Everyday Action Slips
Type of slip: Habit intrusion/'double capture slip'
Analysis: Incorrect motor schema is activated during a task due to failure of sustained focal attention to the task in working memory
Example: Going to the kitchen sink to wash a dish but finding yourself washing one's hands instead
Analysis: Incorrect motor schema is activated during a task due to failure of sustained focal attention to the task in working memory
Example: Going to the kitchen sink to wash a dish but finding yourself washing one's hands instead
Alternatively, given that the PM was used to operating simulators, what conditions could have prompted him to do a sequence that was familiar to him of resetting the simulator (including operating the FCS switches), doing things that are inadvisable in a real aircraft?
If these are stupid questions, I apologise for taking up a mod's time processing the comment deletion.
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, 20:48:00 GMT
permalink Post: 11921640
Thanks for confirming - the point I'm trying to make (apparently badly) is twofold:
1. There's a discussion here about the delay of 4 seconds between switching engine 1 and engine 2 to RUN. The fact is that this is irrelevant in terms of outcome given the lack of APU at the start of this process. Moreover if the lack of APU was known to the pilots, then it would potentially explain this delay anyway (what was the point in flicking the other switch yet)?
2. The lack of APU until at least 12-13 seconds after loss of engines, lack of electrical power from the engines, and at best limited electrical power from the RAT (and for a time, none), would have affected other systems used by the pilots during this short flight, at least for part of it. This hasn't been discussed basically at all, despite a lot of discussion around the ten second delay to start the engines restart, even though that power loss would have been in that window.
1. There's a discussion here about the delay of 4 seconds between switching engine 1 and engine 2 to RUN. The fact is that this is irrelevant in terms of outcome given the lack of APU at the start of this process. Moreover if the lack of APU was known to the pilots, then it would potentially explain this delay anyway (what was the point in flicking the other switch yet)?
2. The lack of APU until at least 12-13 seconds after loss of engines, lack of electrical power from the engines, and at best limited electrical power from the RAT (and for a time, none), would have affected other systems used by the pilots during this short flight, at least for part of it. This hasn't been discussed basically at all, despite a lot of discussion around the ten second delay to start the engines restart, even though that power loss would have been in that window.
Ok so:
1) There may be a technical reason outside of my scope for what you describe. From an operational point of view, for every EFATO I\x92ve ever done in the sim we are taught ANC. Initially our primary focus is flying the aircraft, hence why it\x92s being suggested this was the work of the PM, the only one with sufficient capacity capable of such at that moment. The fact the APU hasn\x92t come online whilst under such workload whilst falling out of the sky at 300ft wouldn\x92t be much of a consideration from the PF
2) Without power, altitude or airspeed nothing else really matters at that stage, does it? The APU takes longer to come online than this flight lasted!
July 13, 2025, 20:52:00 GMT
permalink Post: 11921644
What I'm trying to understand is whether this situation contributed to startle, and goes part of the way to explaining the 10 seconds delay between CUTOFF and RUN that some are discussing. That's it really.
July 13, 2025, 20:53:00 GMT
permalink Post: 11921645
Non-pilot here.
For those interested in reading more about 'action slips', including performing one routine function in place of another, the following free-access article goes into more detail:
Wiley Online Library: Oops! I Did it Again: The Psychology of Everyday Action Slips
As other people have perspicaciously pointed out, assuming that it was the Pilot Monitoring that transitioned the Fuel Cut-Off Switches from RUN to CUTOFF, what action would they likely have been attempting to perform at that stage of the flight for an action slip to be a likely possibility?
Alternatively, given that the PM was used to operating simulators, what conditions could have prompted him to do a sequence that was familiar to him of resetting the simulator (including operating the FCS switches), doing things that are inadvisable in a real aircraft?
If these are stupid questions, I apologise for taking up a mod's time processing the comment deletion.
For those interested in reading more about 'action slips', including performing one routine function in place of another, the following free-access article goes into more detail:
Wiley Online Library: Oops! I Did it Again: The Psychology of Everyday Action Slips
As other people have perspicaciously pointed out, assuming that it was the Pilot Monitoring that transitioned the Fuel Cut-Off Switches from RUN to CUTOFF, what action would they likely have been attempting to perform at that stage of the flight for an action slip to be a likely possibility?
Alternatively, given that the PM was used to operating simulators, what conditions could have prompted him to do a sequence that was familiar to him of resetting the simulator (including operating the FCS switches), doing things that are inadvisable in a real aircraft?
If these are stupid questions, I apologise for taking up a mod's time processing the comment deletion.
I\x92m inclined to give equal wait to intentional shutting down the engines (suicide, if you will) and \x93action-slip\x94. Three seconds after WOW and calling for \x93gear up\x94 is quick but not hugely so. We don\x92t have the transcript, we don\x92t know if the voices were associated with which pilots. It\x92s entirely possible, there was \x93positive rate\x94, \x93gear up\x94 exchange followed by the movement of the switches by the PM, followed by \x93why did you cut off\x94 by the PF who is soon without a PFD.
As to timing, in high stress situations, the mind can run like a computer slowing time or just the opposite, time speeds up and seconds go by trying to comprehend the situation. I was in an ejection, I could spends 15 minutes describing what happened in 500 milliseconds.
July 13, 2025, 21:10:00 GMT
permalink Post: 11921659
Startle will absolutely play a role, largely because no pilot is ever trained to deal with both FCS being cutoff a few seconds after rotate\x85 that would be suicide, for want of a better word.
July 14, 2025, 00:08:00 GMT
permalink Post: 11921795
The two fuel cutoff switches were put in the OFF position. If you have ever used those switches yourself, you will know that it can not be accidental. A deliberate action from one of the pilots is BY FAR the most plausible (or only) explanation. I feel very sorry for the innocent pilot in the cockpit and the hundreds of other victims. Having passed many medical examinations, I can assure you that psychological testing is not part of the periodic medicals.
It does appear to me that you're NOT open to evidence if you continue to deny that a deliberate pilot action is not plausible.
Please enlighten me about how much time you have spent in an airline cockpit... Judging by what you contribute I suspect it will not be much.
July 14, 2025, 03:46:00 GMT
permalink Post: 11921841
My belief is that CVideoRs, with robust protections and legislation around their use, will help accident investigations immensely by answering some of the what questions that the FDR and CVR don't seem able to. It doesn't have to be set up like the many Go-Pro images that are on social media. All that is needed is an image of the center console and the engine display and EICAS/ECAM screens .There would be no need to have images of the pilots faces.
Originally Posted by
Lonewolf 50
Disagree. It creates a hostile work environment. You don't need that in the cockpit / on the flight deck.
Just need to ask: are you involved in airline management?
Just need to ask: are you involved in airline management?
Granted, accident investigates are good at what they do, and I'm in awe of their ability to reconstruct the majority of accidents to determine the ultimate cause (without video). but when technology is available that would have already solved this accident ie. "On-board CCTV shows the Effo selecting the engine run switches to OFF for reasons that remain under investigation" (and to be clear, I AM NOT suggesting that's actually what happened...), it would solve a lot of issues and put to bed speculation about what actually happened to the fuel control switches, who did what and when and I'm at a genuine loss as to why people would argue against it, when it's already so widespread and entrenched in other industries.
Even now - with the preliminary report, I haven't seen mention of which pilot asked the other "Why did you [go to] CUTOFF?" whereas a video would have already told the whole story of this accident - with the exception of the why?
July 14, 2025, 04:55:00 GMT
permalink Post: 11921857
Just to clarify, I'm not aware of any confirmation at this point that the Fuel Cutoff switches were
physically
moved from RUN to CUTOFF and back again.
We do have evidence that the FDR, thus the databus, received signals that the Fuel Cutoff switches were in the RUN position, then the signals changed to CUTOFF one second apart, and then back to RUN at four second intervals.
In the absence of video, we could only use CVR data to determine that the switches were physically moved - either through flight crew conversation or sound of switches being moved.
When the PF asks why the PNF "Why did you cut off" we don't know whether he concluded the fuel was cutoff by checking the physical position of the switches or through instrument annunciations.
I accept that with sampling rates the physical movement of switches to CUTOFF at one second intervals could be logically explained. I can understand why there would be such an interval between physically moving the two switches back to RUN, unless there was some sort of struggle which presumably would be easily detectable on CVR.
Unless I've missed something, I'm not ready to conclude that the switches ever physically moved.
We do have evidence that the FDR, thus the databus, received signals that the Fuel Cutoff switches were in the RUN position, then the signals changed to CUTOFF one second apart, and then back to RUN at four second intervals.
In the absence of video, we could only use CVR data to determine that the switches were physically moved - either through flight crew conversation or sound of switches being moved.
When the PF asks why the PNF "Why did you cut off" we don't know whether he concluded the fuel was cutoff by checking the physical position of the switches or through instrument annunciations.
I accept that with sampling rates the physical movement of switches to CUTOFF at one second intervals could be logically explained. I can understand why there would be such an interval between physically moving the two switches back to RUN, unless there was some sort of struggle which presumably would be easily detectable on CVR.
Unless I've missed something, I'm not ready to conclude that the switches ever physically moved.
July 14, 2025, 06:18:00 GMT
permalink Post: 11921886
Nevertheless he glosses over / ignores the fact that the crew comments are not time stamped, and as such you cannot base much on the time delta until the switches were returned to their normal position. It could be 1 second or 9. I wonder why the decision was made to omit that time stamp in the Prelim Report.
Last edited by compressor stall; 14th July 2025 at 06:28 .
July 14, 2025, 06:38:00 GMT
permalink Post: 11921895
