July 13, 2025, 00:49:00 GMT
permalink Post: 11920969
But there was electrical power to the switch.
July 13, 2025, 01:05:00 GMT
permalink Post: 11920974
FCS poles
It is worth remembering that each switch has 4 poles. Think of a pole as a section of the switch. Each section controls a different function - reporting switch position to FDR, fuel cut off and so on. The chances of anything other than real physical switch movement (whether it be spilt liquid, wiring damage, loose canon plug or whatever) changing the status of all 4 sections is impossibly small. Then you have two switches.
Last edited by Alty7x7; 13th July 2025 at 01:48 .
July 13, 2025, 01:46:00 GMT
permalink Post: 11920981
If the switches were without power (!), then the FDR could not record them \x91transistioning\x92. This obsession with \x91position\x92 is weird. The FDR is a DATA recorder. For example it knows the position of the thrust levers because position is used to determine how much thrust is demanded. But of course that\x92s a huge simplification. But binary switches are on or off and do NOT have a \x91position\x92.
July 13, 2025, 01:51:00 GMT
permalink Post: 11920984
Would not expect an FDR dedicated pole. They
might
pull the FCS position from the FADEC, since what really matters is what the FADEC receives as a command. I would expect two poles dedicated to the two circuits, one routed to each FADEC channel, and the others to the non-FADEC-reset-command functions.
July 13, 2025, 06:47:00 GMT
permalink Post: 11921059
The pin groupings are usually in 3's.
e.g.
1,2,3 is one pole
4,5,6 is another
7,8,9 etc.
I have one 787 fuel control diagram which suggests 3, but there may be more
Thanks in advance
July 13, 2025, 06:59:00 GMT
permalink Post: 11921065
Would not expect an FDR dedicated pole. They
might
pull the FCS position from the FADEC, since what really matters is what the FADEC receives as a command. I would expect two poles dedicated to the two circuits, one routed to each FADEC channel, and the others to the non-FADEC-reset-command functions.
The 747 has 3 poles per switch. To send signals to all the systems it needs to, splices and multi-output relays are involved. On some aircraft there are even separate power sources going to some of these poles.
July 13, 2025, 07:13:00 GMT
permalink Post: 11921074
I have a simplified 787 fuel control diagram showing 3 outputs from the fuel control levers. I suspect it represents poles. One signal goes to the EEC for "reset". One signal goes the fuel valves. Another signal goes to a Remote Data Concentrator where the signal is digitised and sent to innumerable devices (including the EEC and the FDR). That is not to say there are more. I don't see a line to the wing spar valve.
The 747 has 3 poles per switch. To send signals to all the systems it needs to, splices and multi-output relays are involved. On some aircraft there are even separate power sources going to some of these poles.
The 747 has 3 poles per switch. To send signals to all the systems it needs to, splices and multi-output relays are involved. On some aircraft there are even separate power sources going to some of these poles.
July 13, 2025, 13:28:00 GMT
permalink Post: 11921324
I agree with sabenaboy.
The subject of pilot suicide is not distasteful, but for many it is taboo.
I understand this. Many historical accidents caused by pilot incompetence could well have been quickly labelled as suicide, only for their errors to show up in the subsequent investigation.
Looking for a rational explanation is a normal way to go, and suicide is not rational in most peoples' eyes.
However, this tragic event looks highly probable to have been caused by a deliberate action. And shutting off the fuel controls immediately following rotation is impossible to justify as an accidental move.
I remember calling the German Wings accident as a likely suicide event as soon as I heard about it. Nevertheless I was open to hostility and recriminations on this website for quite a few days, once my carefully-worded contribution was not deleted.
I do wonder if any further information can be gleaned from the FDR, which has not already been shared. I hope so. And of course, the CVR contents require further analysis.
Nobody in their right minds takes any pleasure, woke or not, from learning of a suicide, particularly one that involves the death of many innocent people.
The subject of pilot suicide is not distasteful, but for many it is taboo.
I understand this. Many historical accidents caused by pilot incompetence could well have been quickly labelled as suicide, only for their errors to show up in the subsequent investigation.
Looking for a rational explanation is a normal way to go, and suicide is not rational in most peoples' eyes.
However, this tragic event looks highly probable to have been caused by a deliberate action. And shutting off the fuel controls immediately following rotation is impossible to justify as an accidental move.
I remember calling the German Wings accident as a likely suicide event as soon as I heard about it. Nevertheless I was open to hostility and recriminations on this website for quite a few days, once my carefully-worded contribution was not deleted.
I do wonder if any further information can be gleaned from the FDR, which has not already been shared. I hope so. And of course, the CVR contents require further analysis.
Nobody in their right minds takes any pleasure, woke or not, from learning of a suicide, particularly one that involves the death of many innocent people.
There is always some virtue signalling poster on all these threads saying “we shouldn’t speculate until the full report comes out”…I’m not one of those, but I’m happy to call out someone pointing the finger when the available evidence still very inconclusive. I hope the mods frustrate him further by deleting his efforts.
July 13, 2025, 13:42:00 GMT
permalink Post: 11921331
I agree with sabenaboy.
The subject of pilot suicide is not distasteful, but for many it is taboo.
I understand this. Many historical accidents caused by pilot incompetence could well have been quickly labelled as suicide, only for their errors to show up in the subsequent investigation.
Looking for a rational explanation is a normal way to go, and suicide is not rational in most peoples' eyes.
However, this tragic event looks highly probable to have been caused by a deliberate action. And shutting off the fuel controls immediately following rotation is impossible to justify as an accidental move.
I remember calling the German Wings accident as a likely suicide event as soon as I heard about it. Nevertheless I was open to hostility and recriminations on this website for quite a few days, once my carefully-worded contribution was not deleted.
I do wonder if any further information can be gleaned from the FDR, which has not already been shared. I hope so. And of course, the CVR contents require further analysis.
Nobody in their right minds takes any pleasure, woke or not, from learning of a suicide, particularly one that involves the death of many innocent people.
The subject of pilot suicide is not distasteful, but for many it is taboo.
I understand this. Many historical accidents caused by pilot incompetence could well have been quickly labelled as suicide, only for their errors to show up in the subsequent investigation.
Looking for a rational explanation is a normal way to go, and suicide is not rational in most peoples' eyes.
However, this tragic event looks highly probable to have been caused by a deliberate action. And shutting off the fuel controls immediately following rotation is impossible to justify as an accidental move.
I remember calling the German Wings accident as a likely suicide event as soon as I heard about it. Nevertheless I was open to hostility and recriminations on this website for quite a few days, once my carefully-worded contribution was not deleted.
I do wonder if any further information can be gleaned from the FDR, which has not already been shared. I hope so. And of course, the CVR contents require further analysis.
Nobody in their right minds takes any pleasure, woke or not, from learning of a suicide, particularly one that involves the death of many innocent people.
Mental impairment is a huge and not well understood spectrum. Sometimes it\x92s dark and criminal; sometimes it\x92s long term disease related (Alzheimer\x92s, etc), sometimes acute (stroke), sometimes chemical and mental imbalance developing over a shorter time period (like the US Captain who had a paranoid like episode inflight, or the jumpseater in the US trying to shut down both engines but restrained by crew). In many cases it\x92s impossible to see coming and doesn\x92t even have to involve criminal/homicidal/psychotic intent. It can simply be a stroke or episode which causes confusion and someone to start grabbing at switches best left untouched \x97 perhaps while thinking he is doing the correct actions. So one can not ignore the possibility that a crew member suffered some sort of cognitive episode resulting in shutting off the FCS; perhaps thinking he was back in the chocks for a few minutes. And then forgetting he\x92d done it.
These events may be exacerbated by the huge stigma associated with a pilot attempting to seek counseling or mental health help (even for a relatively small problem which can untreated develop into a much larger one). Out of fear of repercussions of falling into that medical \x91black hole\x92 and trying to get re-certified for even minor mental health glitches.
July 13, 2025, 15:35:00 GMT
permalink Post: 11921397
Since some posters seem focused on the theory that the fuel control switches didn't move - just the electric output did (and as I posted earlier, the FDR only knows electrical states, there is literally no other way for the FDR to monitor the switch position).
So I did a little thought experiment. Uncommanded engine shutdowns (for all causes) are already rare - a 10-6 event. Now, during my 40 year career, I can't remember ever encountering a case where the fuel shutoff was commanded without a corresponding movement of the fuel switch. However in this industry it's a good idea to 'never say never', so let's assume it's happened. It would take something like a hot short to cause it to happen (moving the voltage from RUN to CUTOFF) since an open circuit will simply leave the valves where they were. That would put its probability way out there - something like 10-8/hr.
The left and right engine wiring is physically isolated from the other engine - nothing gets routed in common bundles between the engines. Hence there is simply no way a localized issue could affect both engine's wire bundles. So we're talking two independent events that cause the switch output to electrical change state between RUN and CUTOFF without associated switch movement. So now were out in a 10-16/hr. territory. Now, these independent events both occur a second apart - 3,600 seconds/hr., so we've just added ~8 orders of magnitude to the dual failure probability number (10-24/hr.). Now, they both somehow return to normal withing a few seconds of each other - another ~8 orders of magnitude so we're talking 10-32.
That means the probability of this happening at any time since the Big Bang is way less than one....
Space aliens look reasonable in comparison. So can we discuss things that might actually have happened?
So I did a little thought experiment. Uncommanded engine shutdowns (for all causes) are already rare - a 10-6 event. Now, during my 40 year career, I can't remember ever encountering a case where the fuel shutoff was commanded without a corresponding movement of the fuel switch. However in this industry it's a good idea to 'never say never', so let's assume it's happened. It would take something like a hot short to cause it to happen (moving the voltage from RUN to CUTOFF) since an open circuit will simply leave the valves where they were. That would put its probability way out there - something like 10-8/hr.
The left and right engine wiring is physically isolated from the other engine - nothing gets routed in common bundles between the engines. Hence there is simply no way a localized issue could affect both engine's wire bundles. So we're talking two independent events that cause the switch output to electrical change state between RUN and CUTOFF without associated switch movement. So now were out in a 10-16/hr. territory. Now, these independent events both occur a second apart - 3,600 seconds/hr., so we've just added ~8 orders of magnitude to the dual failure probability number (10-24/hr.). Now, they both somehow return to normal withing a few seconds of each other - another ~8 orders of magnitude so we're talking 10-32.
That means the probability of this happening at any time since the Big Bang is way less than one....
Space aliens look reasonable in comparison. So can we discuss things that might actually have happened?
Now my operator had an incident on a 757 in cruise about 10 years ago where the spar valve closed without command. The SPAR VALVE light will probably have lit up (can\x92t remember) but the engine died. From crz thrust to no thrust in seconds.
So such things are not unknown.
July 13, 2025, 19:09:00 GMT
permalink Post: 11921545
I've been following this with interest from the start. My very first reaction when I saw it was that it was a double-engine failure, clearly I was intrigued to know whether it was pilot or system initiated.
I don't think from what we've told that you can draw a conclusion either way. The data shows that the FDR recorded both fuel switches being off, then back to on. The crucial piece here is that it's only a signal from the system, not a physical check of switch position, that provides the signal.
It's entirely possible that the physical switches were not moved. The CVR recording of the other pilot stating that he didn't move them is fascinating in this context.
I don't think from what we've told that you can draw a conclusion either way. The data shows that the FDR recorded both fuel switches being off, then back to on. The crucial piece here is that it's only a signal from the system, not a physical check of switch position, that provides the signal.
It's entirely possible that the physical switches were not moved. The CVR recording of the other pilot stating that he didn't move them is fascinating in this context.
July 13, 2025, 19:47:00 GMT
permalink Post: 11921581
I\x92m at a loss as to why the discussion of an apu inlet door is relevant as it\x92s been clearly stated in the report to be working as per the conditions that were met.
July 13, 2025, 20:03:00 GMT
permalink Post: 11921594
Because it wouldnt have been immediately available to support engine restart and/or other electrical functions, as it didn't open until around 13 seconds after cutoff event. It's relevant in so much of how it may (or may not) have affected recovery efforts.
It was working as per the conditions absolutely, but those conditions meant it wasn't available immediately.
It was working as per the conditions absolutely, but those conditions meant it wasn't available immediately.
July 13, 2025, 20:08:00 GMT
permalink Post: 11921598
The question is what impact was had on attempts to recover the aircraft by the (presumed) lack of most or all electrical power.
July 13, 2025, 20:28:00 GMT
permalink Post: 11921620
Could be - we have a group of some 200 or so oldies ex. airline who had a thrash at this subject this morning - if you know how the system works (FDR, CVR, accident investigation, etc.) you could suggest that you could manipulate the scenario and that it would be hard to prove who actually did it. The transcripts with the actual words, tones and emotions could well point to who did it but could it be proved?
July 13, 2025, 20:33:00 GMT
permalink Post: 11921623
Could be - we have a group of some 200 or so oldies ex. airline who had a thrash at this subject this morning - if you know how the system works (FDR, CVR, accident investigation, etc.) you could suggest that you could manipulate the scenario and that it would be hard to prove who actually did it. The transcripts with the actual words, tones and emotions could well point to who did it but could it be proved?
July 13, 2025, 22:36:00 GMT
permalink Post: 11921747
While this is thread is still deeply into hamster wheel status, there are some valuable inputs being made. I'll try to continue with that...
Thrust lever position post-accident - it takes very little force to move the thrust levers, a little more than one pound-force at the knob. I'd be very surprised if the post impact position was the same as pre-impact (and lever angle is recorded on the FDR, so the investigators know where they were). In short - the post-accident lever position is not meaningful.
Fuel condition switch position detents - if the Indian investigators had any reason to believe that a failed or inoperative detent was a contributing fact, the authorities would have ordered a fleet-wide inspection (especially since it literally takes only seconds to do the inspection - the paperwork would take many times longer than the actual inspection).
Engine restart (i.e. "Quick Windmill Relight"): Even if the igniters were firing, at high power they won't actually spark (the electrical resistance or the air at several hundred psi prevents a spark) - so they won't spark until you get down somewhere near idle if you're close to sea level. Once the engine has dropped below the min idle, it takes a long time for it accelerate back to even an idle condition. At takeoff power, the compressor components get very hot - do a power cut the air coming in the compressor gets heated by the residual heat in the compressor. This in turn limits how fast you can add fuel in the burner without excessively back pressuring the compressor and causing a compressor stall. So it actually takes longer for the engine to accel to idle that it would during a normal (cold engine) start. The 5 seconds to 95% accel requirement referenced earlier is from a stable 'high' idle (we typically call it 'approach idle' since it's automatically selected when landing flaps are selected). Approach idle is ~10% N2 higher than the in-flight minimum idle, so that takes several more seconds. Bottom line, after initiating the Quick Windmill Relight, you're not going to have usable thrust for at least 30 seconds - probably closer to 60 seconds.
For all the complaining about this preliminary report, it actually goes into more detail than is typical.
BTW, my money is still on the 'muscle memory/action slip' or whatever you want to call it. I can easily imagine a scenario along the line of 'why did you turn off the fuel' - 'I didn't - oh wait - oh
...
Thrust lever position post-accident - it takes very little force to move the thrust levers, a little more than one pound-force at the knob. I'd be very surprised if the post impact position was the same as pre-impact (and lever angle is recorded on the FDR, so the investigators know where they were). In short - the post-accident lever position is not meaningful.
Fuel condition switch position detents - if the Indian investigators had any reason to believe that a failed or inoperative detent was a contributing fact, the authorities would have ordered a fleet-wide inspection (especially since it literally takes only seconds to do the inspection - the paperwork would take many times longer than the actual inspection).
Engine restart (i.e. "Quick Windmill Relight"): Even if the igniters were firing, at high power they won't actually spark (the electrical resistance or the air at several hundred psi prevents a spark) - so they won't spark until you get down somewhere near idle if you're close to sea level. Once the engine has dropped below the min idle, it takes a long time for it accelerate back to even an idle condition. At takeoff power, the compressor components get very hot - do a power cut the air coming in the compressor gets heated by the residual heat in the compressor. This in turn limits how fast you can add fuel in the burner without excessively back pressuring the compressor and causing a compressor stall. So it actually takes longer for the engine to accel to idle that it would during a normal (cold engine) start. The 5 seconds to 95% accel requirement referenced earlier is from a stable 'high' idle (we typically call it 'approach idle' since it's automatically selected when landing flaps are selected). Approach idle is ~10% N2 higher than the in-flight minimum idle, so that takes several more seconds. Bottom line, after initiating the Quick Windmill Relight, you're not going to have usable thrust for at least 30 seconds - probably closer to 60 seconds.
For all the complaining about this preliminary report, it actually goes into more detail than is typical.
BTW, my money is still on the 'muscle memory/action slip' or whatever you want to call it. I can easily imagine a scenario along the line of 'why did you turn off the fuel' - 'I didn't - oh wait - oh
...
July 13, 2025, 22:58:00 GMT
permalink Post: 11921757
While this is thread is still deeply into hamster wheel status, there are some valuable inputs being made. I'll try to continue with that...
Thrust lever position post-accident - it takes very little force to move the thrust levers, a little more than one pound-force at the knob. I'd be very surprised if the post impact position was the same as pre-impact (and lever angle is recorded on the FDR, so the investigators know where they were). In short - the post-accident lever position is not meaningful.
Fuel condition switch position detents - if the Indian investigators had any reason to believe that a failed or inoperative detent was a contributing fact, the authorities would have ordered a fleet-wide inspection (especially since it literally takes only seconds to do the inspection - the paperwork would take many times longer than the actual inspection).
Engine restart (i.e. "Quick Windmill Relight"): Even if the igniters were firing, at high power they won't actually spark (the electrical resistance or the air at several hundred psi prevents a spark) - so they won't spark until you get down somewhere near idle if you're close to sea level. Once the engine has dropped below the min idle, it takes a long time for it accelerate back to even an idle condition. At takeoff power, the compressor components get very hot - do a power cut the air coming in the compressor gets heated by the residual heat in the compressor. This in turn limits how fast you can add fuel in the burner without excessively back pressuring the compressor and causing a compressor stall. So it actually takes longer for the engine to accel to idle that it would during a normal (cold engine) start. The 5 seconds to 95% accel requirement referenced earlier is from a stable 'high' idle (we typically call it 'approach idle' since it's automatically selected when landing flaps are selected). Approach idle is ~10% N2 higher than the in-flight minimum idle, so that takes several more seconds. Bottom line, after initiating the Quick Windmill Relight, you're not going to have usable thrust for at least 30 seconds - probably closer to 60 seconds.
For all the complaining about this preliminary report, it actually goes into more detail than is typical.
BTW, my money is still on the 'muscle memory/action slip' or whatever you want to call it. I can easily imagine a scenario along the line of 'why did you turn off the fuel' - 'I didn't - oh wait - oh
...
Thrust lever position post-accident - it takes very little force to move the thrust levers, a little more than one pound-force at the knob. I'd be very surprised if the post impact position was the same as pre-impact (and lever angle is recorded on the FDR, so the investigators know where they were). In short - the post-accident lever position is not meaningful.
Fuel condition switch position detents - if the Indian investigators had any reason to believe that a failed or inoperative detent was a contributing fact, the authorities would have ordered a fleet-wide inspection (especially since it literally takes only seconds to do the inspection - the paperwork would take many times longer than the actual inspection).
Engine restart (i.e. "Quick Windmill Relight"): Even if the igniters were firing, at high power they won't actually spark (the electrical resistance or the air at several hundred psi prevents a spark) - so they won't spark until you get down somewhere near idle if you're close to sea level. Once the engine has dropped below the min idle, it takes a long time for it accelerate back to even an idle condition. At takeoff power, the compressor components get very hot - do a power cut the air coming in the compressor gets heated by the residual heat in the compressor. This in turn limits how fast you can add fuel in the burner without excessively back pressuring the compressor and causing a compressor stall. So it actually takes longer for the engine to accel to idle that it would during a normal (cold engine) start. The 5 seconds to 95% accel requirement referenced earlier is from a stable 'high' idle (we typically call it 'approach idle' since it's automatically selected when landing flaps are selected). Approach idle is ~10% N2 higher than the in-flight minimum idle, so that takes several more seconds. Bottom line, after initiating the Quick Windmill Relight, you're not going to have usable thrust for at least 30 seconds - probably closer to 60 seconds.
For all the complaining about this preliminary report, it actually goes into more detail than is typical.
BTW, my money is still on the 'muscle memory/action slip' or whatever you want to call it. I can easily imagine a scenario along the line of 'why did you turn off the fuel' - 'I didn't - oh wait - oh
...
The EAFR data revealed that the thrust levers remained
forward (takeoff thrust) until the impact.
Would that position be consistent with a restart attempt?
July 13, 2025, 23:45:00 GMT
permalink Post: 11921784
The released FDR data is quite detailed. Enough to answer what, when & how beyond all reasonable doubt
The released CVR data is conspicuously less detailed.Herein lies who & maybe why
The next phase of the investigation may need to be led by other investigative bodies.
Authority gradients likely significant
Did Captain cut fuel, get challenged by FO, and then fuel turned back on too late?
Or did Captain cut fuel, accuse FO to get it on the record, and then fuel turned back on too late?
If FO cut fuel, would expect a more assertive comment and faster intervention.
The released CVR data is conspicuously less detailed.Herein lies who & maybe why
The next phase of the investigation may need to be led by other investigative bodies.
Authority gradients likely significant
Did Captain cut fuel, get challenged by FO, and then fuel turned back on too late?
Or did Captain cut fuel, accuse FO to get it on the record, and then fuel turned back on too late?
If FO cut fuel, would expect a more assertive comment and faster intervention.
July 14, 2025, 00:26:00 GMT
permalink Post: 11921800
Did Captain cut fuel, get challenged by FO, and then fuel turned back on too late?
Or did Captain cut fuel, accuse FO to get it on the record, and then fuel turned back on too late?
If FO cut fuel, would expect a more assertive comment and faster intervention.
Or did Captain cut fuel, accuse FO to get it on the record, and then fuel turned back on too late?
If FO cut fuel, would expect a more assertive comment and faster intervention.
For me the prelim report just reveals an unintended consequence of relying on muscle memory to carry out an action that has been performed multiple times without confirmation. It happens a lot but rarely with such a tragic consequence. I have turned the ignition switch to Normal during an engine start when asked to set the park brake during a pushback. There have been multiple occasions where an A320 park brake was set when a flap setting was commanded. On more than one occasion the flaps have been raised when "gear up" was commanded. This may not have been the first time the FCO switches have been selected but definitely the first time it wasn't picked up early enough to reverse the action.
As to the CVR recordings, I will repeat what I have often stated previously. There is no inherent right of the public to receive a full transcript of the CVR in order for them to form their own opinion of what happened. It is up to the Indian AAIB to conduct an investigation under the requirements of Annex 13 and possibly a fuller transcript of the CVR will be published in the Final Report to help the reader gain an understanding of what happened.
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.