July 13, 2025, 02:44:00 GMT
permalink Post: 11920995
There is one known inadvertent shutdown with this type of switch, on a B744, many years ago, when the Rosen visor fell from the upper sun visor rail when being relocated. That managed to turn off 1 fuel switch.
The report is quite comprehensive for an interim report, and it does not draw any conclusions as yet as to how or why the fuel control discrete is recorded as OFF, however, it is troubling. I would reserve opinion until there is a clear spectral analysis that shows the selection of the fuel switches off, and then back on.
As to the time to react, the crew in this case if unaware of the causation will have a fair recognition time to assimilate the information that is presented, and then to determine that the cause is the switches being off is going to take some time to process, discover the system status and respond, if that is what happened. I remain concerned with liquid ingress to the control system, giving a change in the sensed switch position rather than the selected position. That is looking like a long shot, but then this event is way outside of the normal box.
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July 13, 2025, 03:02:00 GMT
permalink Post: 11920998
Basically, the preliminary report has narrowed down the cause of the disaster and discounted a few earlier theories such as flaps up instead of gear up, but there are a lot of questions still to be answered. We need to know; who, how and why.
The switches could have been set to cut off in error even though this was denied on the CVR. However anyone with experience in this part of the world knows that owning up to mistakes isn't a common practice.
I'd rule out a suicide attempt because if the pilot doing it had moved to switches to cut off and the other pilot had put them back on, a hard push forward on the control column at that height would have settled the matter.
I'm not yet convinced that the aircraft isn't responsible due to a technical fault or improper maintenance.
The switches could have been set to cut off in error even though this was denied on the CVR. However anyone with experience in this part of the world knows that owning up to mistakes isn't a common practice.
I'd rule out a suicide attempt because if the pilot doing it had moved to switches to cut off and the other pilot had put them back on, a hard push forward on the control column at that height would have settled the matter.
I'm not yet convinced that the aircraft isn't responsible due to a technical fault or improper maintenance.
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July 13, 2025, 03:50:00 GMT
permalink Post: 11921007
Last edited by Sizzling_foil; 13th July 2025 at 04:11 .
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July 13, 2025, 04:15:00 GMT
permalink Post: 11921010
You want these switches within reach of both pilots, in a position where hands are not constantly passing over them, able to be actioned quickly, to be internally guarded (= require 2 distinct actions to move) as well as externally protected (side guards). It also seems logical to have them near the thrust levers.
Boeing have achieved all this.
It feels like it would be an error to try and redesign these switches in light of this incident. The switches operated as they were commanded.
Boeing have achieved all this.
It feels like it would be an error to try and redesign these switches in light of this incident. The switches operated as they were commanded.
The switches must be accessible - Yes
They are where hands regularly pass over them - a No. As I see it, a certain expression regarding the back end of a male dog comes to mind!
Able to be actioned quickly - arguably, currently, it's much too quickly, IMHO.
Guarded - when it comes to Cerebellum (Yes, please search that word in this thread)-generated actions, that makes zero difference. When the Cerebellum has been trained and learned, it will repeat the most complex sequences you can think of - without you having to think of them. That's the REAL problem that needs to be solved.
Logical - Yes, but really No! Putting them close together can more easily result in the wrong action at times of high stress, confusion, fear, danger, urgency, whatever.
I say they need a major, i.e. Total redesign.
But one of the big problems is that these two switches are used at least a couple of times on every flight. So, they are true Cerebellum Fodder.
However, here's one suggestion. The modern plane is full of sensors, interlocks and logic devices. Use them a bit smarter, I say!
When the plane is on the ground, allow the Fuel Switches to be turned On and Off without debate. But using Air/Ground and /(or?) WoW, when the plane is in the air, the process must be made markedly different. At the very LEAST, make them properly guarded, so a flap must be lifted to action them. And as soon as the flap gets lifted in flight, a very loud alarm and maybe a light is triggered. Then, everybody knows, no need for guessing. Until you or your fellow pilot presses the Confirm button somewhere nearby, the switches can't be moved - or are disabled, or something.
If you don't regularly use this procedure, the Cerebellum won't be so likely to Run It Automatically in a panicked rush. The different process from what you did just at the start of the flight will trip up the cerebellum somewhat, and trigger the Higher Brain to start thinking...: "What? Is this correct?"
How about this?
Subsequent thoughts: The Confirm button would only remain live for a short period, say 3 seconds, during which time, you can operate the switch. Then it resets.
Another idea: Leave the Fuel Cutoff switches right where they are, as they are. But, when in Flight, totally disable them. Alarm if moved. Put the In-Flight Shutoff switches in the overhead panel, with the same kind of aural/visual Confirmation-required warning system permanently operative.
P.P.S. That may not be enough, maybe there needs to be a Takeoff speed transition added - i.e. Before Rotate. Maybe just after V1?
Last edited by MaybeItIs; 13th July 2025 at 04:48 . Reason: add the subs.
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July 13, 2025, 04:27:00 GMT
permalink Post: 11921012
I have only seen a diagram for I think the 737. I remember there being a listing of what each pole did, but I can no longer find the post.
My expectation/speculation, though, is this:
The EAFR gets its information on cutoff switch position from the FADECs via data buses, similar to almost all other engine data. We have N2 information in the report after the engines were switched off, so clearly there are no concerns about this data not being captured.
This means that the FADEC's data of where the switches are is almost certainly the EAFR's data.
There are other poles on the switches that do other things - I think it was opening/closing the LPSOV and enabling the generators. The fourth pole in the 'cutoff' position was IIRC not used because the generators don't get a disable signal, whereas the LPSOVs are powered open in the run position and powered closed in the cutoff position.
If the switches were physically operated and in good electromechanical condition (not counting the possibly faulty gates), we would expect all four poles to operate essentially simultaneously, with the four 'run' contacts opening and the four 'cutoff' contacts closing. Not only would the EAFR pick up that the FADECs were commanded off, but also that the LPSOV closes after a short delay, and the generators drop offline before N2 drops below idle.
When the switches are moved back to run, we would likewise see the position of each LPSOV return to open.
(this does not necessarily mean that a person intentionally operated them, but that the lever actually moved).
If there was a wiring fault, contamination, or internal switch failure, we would probably not see this. Instead, you might see the LPSOV remain open despite the engine shutting down, or perhaps the FADECs trying to keep the engine running while the LPSOV has closed and shut off fuel, or the two FADEC channels receiving different run/cutoff signals - and all of this would probably happen differently on each engine (if it affected both engines at all). There is no indication of this in the report.
These are not your basic light switch where the load is either powered or not powered. They're four switches ganged together and operated in unison, and each channel powers either thing A or thing B. If you have both or neither A & B powered (for longer than the ~50ms that the switch takes to move between positions), this is a fault that should be visible in the EAFR data in some/many cases. Think valves being displayed in orange as 'position unknown'.
If all run contacts opened, and all cutoff contacts closed, the switch moved from run to cutoff .
I don't know whether they analysed the EAFR data in this much detail yet, but coupled with a potential click sound on the CVR, I think there's going to be very very little doubt at the end of the investigation whether the switches physically moved or not, and I strongly expect they did.
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July 13, 2025, 05:12:00 GMT
permalink Post: 11921023
Just a thought \x97 the fire extinguisher handles perform the same function as the fuel cut-off.
Could there have been a strap /booklet or something else that accidentally got under the fire handles and activated them when one of the pilots pulled on the item?
The fire handles are not particularly well protected against something getting underneath them
Is there any information on whether the fuel cutoff switches and fire handles register as separate events on the flight data recorder, or if both are logged under a common indication, such as 'fuel switch cut off'?
Could there have been a strap /booklet or something else that accidentally got under the fire handles and activated them when one of the pilots pulled on the item?
The fire handles are not particularly well protected against something getting underneath them
Is there any information on whether the fuel cutoff switches and fire handles register as separate events on the flight data recorder, or if both are logged under a common indication, such as 'fuel switch cut off'?
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July 13, 2025, 05:16:00 GMT
permalink Post: 11921026
@Maybeitis,
how about we leave the total redesign of the fuel switch locations and operation (which have been moved billions of times in thousands of aircraft without a hitch) until the final report is out.
These were deliberately moved. It wasn't a brain-fart. Unless the interim report omits crew calls which turn the scenario on it's head.
These were deliberately moved. It wasn't a brain-fart. Unless the interim report omits crew calls which turn the scenario on it's head.
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July 13, 2025, 05:36:00 GMT
permalink Post: 11921035
It is incomprehensible to conceive of someone deliberately shutting off the engines. For good reason the interim report does not state that as the cause \x85.. however it makes clear that the switches were moved to cutoff for an as yet unknown reason, and subsequently back to run.
This brought to mind a case many years ago where a pilot had a significant psychiatric disorder that among other things, caused him to have the urge to shutoff engines in flight. I am unable to post a link as I am a newby but if you search Sick Qantas Pilot wanted to crash you will find the story.
As sad as that particular case is, it does reveal that psychiatric issues may (I stress may) have been a trigger for the events that have unfolded on AI 171. There are other physiological events that may result in a person carrying out \x93memory\x94 actions at an in-opportune moment. These include brain tumour or a brain infection. Looking to the medicos for further discussion on these possibilities.
I am sure the investigation will be looking very closely at the autopsy results as well as medical history to determine if a health aspect contributed to the events.
This brought to mind a case many years ago where a pilot had a significant psychiatric disorder that among other things, caused him to have the urge to shutoff engines in flight. I am unable to post a link as I am a newby but if you search Sick Qantas Pilot wanted to crash you will find the story.
As sad as that particular case is, it does reveal that psychiatric issues may (I stress may) have been a trigger for the events that have unfolded on AI 171. There are other physiological events that may result in a person carrying out \x93memory\x94 actions at an in-opportune moment. These include brain tumour or a brain infection. Looking to the medicos for further discussion on these possibilities.
I am sure the investigation will be looking very closely at the autopsy results as well as medical history to determine if a health aspect contributed to the events.
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July 13, 2025, 05:51:00 GMT
permalink Post: 11921038
@Maybeitis,
how about we leave the total redesign of the fuel switch locations and operation (which have been moved billions of times in thousands of aircraft without a hitch) until the final report is out.
These were deliberately moved. It wasn't a brain-fart. Unless the interim report omits crew calls which turn the scenario on it's head.
These were deliberately moved. It wasn't a brain-fart. Unless the interim report omits crew calls which turn the scenario on it's head.
Happy to oblige.
TBH, I'm no longer so concerned with what really happened inside the cockpit of AI171. What the final report says won't make any difference. I can see some flaws in the Boeing design (don't know Airbus so can't compare), and propose a few ideas to deal with that, and with the fact that we humans are highly flawed. Sometimes, the brain doesn't know what the right hand is doing. That's a wee problem.
My theory FWIW, says this won't have been called at all. And that "it" was done entirely without intention. The intention was to do something else. So, in that case, was it deliberate? I say No. It was an accident.
It was IMO, done with the best of intentions, but resulted in a serious blunder, with the wrong switches getting turned off. By what has been termed here "a slip". I agree with that. As I've mentioned, I now believe that when you know someone (including yourself) is doing something wrong, you seem to be more likely to make a mistake yourself. It's as if you automatically become partners in crime. (Even you and yourself!) Did you read this article? Some of the comments are also well worth reading.
https://avherald.com/h?article=48d1e3ae&opt=0
This [i.e 171] accident (I think the correct term) has absolutely fascinated me, and caused me to think a great deal. My recent posts are not really about 171. Only a result of it.
For the benefit of all. You know how people who have lost loved ones want their death to somehow benefit others? I didn't lose anyone in this crash, but that's a beautiful thing about we flawed humans.
I'll shut up now. Thanks for allowing me to participate.
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July 13, 2025, 06:13:00 GMT
permalink Post: 11921045
This accident emphasises the sad fact that HUMANS are the weakest link in the FS chain - particularly now that engineering is much more reliable.
How close are we to having PILOTLESS passenger aircraft ?
I would guess many years?
Computers don\x92t have heart attacks and \x91brain farts \x91 ! BUT garbage IN = garbage OUT !
PS reading the many reports that these cut off switches have been \x91moved \x91 in error they appear to be located in a much too accessible position !
(On the B707 ( AWACS ) they were on the roof panel.)
The explanation that they were switched OFF in error after a STAB TRIM warning seems possibly the most likely cause but would be a major mistake !! is a STAB TRIM problem shortly after T/O potentially a major problem on th B787 ?
How close are we to having PILOTLESS passenger aircraft ?
I would guess many years?
Computers don\x92t have heart attacks and \x91brain farts \x91 ! BUT garbage IN = garbage OUT !
PS reading the many reports that these cut off switches have been \x91moved \x91 in error they appear to be located in a much too accessible position !
(On the B707 ( AWACS ) they were on the roof panel.)
The explanation that they were switched OFF in error after a STAB TRIM warning seems possibly the most likely cause but would be a major mistake !! is a STAB TRIM problem shortly after T/O potentially a major problem on th B787 ?
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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.
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July 13, 2025, 07:18:00 GMT
permalink Post: 11921078
The Action Slip scenario
What is an action slip?
There's a possible scenario we're discussing here that fits all of the available evidence. It proposes that one of the pilots operated the switches in an unconscious action called an "action slip". This is a rote action that we do without conscious thought when we're distracted: we mean to do something, and then we get our signals crossed and do something else. To learn more, search for "action slip" or "cerebellum" on this thread; I hope paulross adds the keyword to the next build of his excellent index at https://paulross.github.io/pprune-th...171/index.html .
How would this scenario play out?
We don't have enough evidence to pin down the exact sequence, so there are some assumptions here that I hope you find plausible. (And obviously it's not the only scenario that fits the evidence.) We especially do not know who did what and why, so that is all guesswork on my part. The times are taken from the preliminary report. The report places the verbal exchange among the pilots where I put it.
———
8:08:39 The 787 becomes airborne. The F/O is pilot flying (PF), with both hands on the yoke. The Captain is PNF (not flying).
8:08:42 The PNF unconsciously flips both fuel switches to CUT OFF, one after the other. This is a rote action performed after each flight, or as training captain in the simulator.
The action cuts power to the engines; they stop delivering thrust almost immediately, and the turbines start slowing down.
The 787 systems disconnect the electrical generators in advance of them failing. The right side
(Captain's side)
of the cockpit l oses power to most instruments. With all 4 generators offline, the RAT deploys to provide emergency power.
The PF feels the cessation of thrust. He looks at the display to see an ENGINES SHUT OFF message. He assumes the PNF shut them off, and asks him why he shut them off. This is the lowest "probe" level on the PACE assertiveness scale; see e.g. https://psychsafety.com/pace-graded-assertiveness/ or search for "probe alert" on pprune if you wish to know more. The highest level of assertiveness, E for "emergency", would have the F/O put the switches back himself immediately, but that would have required a high degree of confidence in the face of the older Captain that may have been difficult to achieve.
Since the action was unconscious, the PNF replies that he did not do that.
8:08:47 The RAT starts delivering hydraulic power, the engines decelerate past idle.
The PNF realizes that engine power is in fact cut. Eventually he checks the switches he thinks he did not touch, sees the engine 1 switch first and flips it back to RUN at 8:08:52. He then thinks to check the second switch and flips it up at 8:08:56.
The accident sequence ensues.
There's really not much the PNF can do at this point. At 8:09:05, he transmits a MAYDAY.
———
Obviously there are variations to this, for example it could have been the PF who put the fuel switches back. (In the above scenario, the PF is focused on flying—aviate!—and never turns his head to see the switches.) My goal was simply to set out a possible sequence, to see whether it feels plausible. Remember, as you see other scenarios put forth, that any issues a person could wrestle with would also be distracting. While both pilots would be very focused during the takeoff run, the moment the aircraft lifted off, the PNF could well have mentally relaxed a little, opening an opportunity for the action slip.
Thoughts?
Edit: I got the roles mixed up; in a fixed scenario, either the Captain was the PF (and may have set the switches to cutoff), or flight control changed over at the power failure.
There's a possible scenario we're discussing here that fits all of the available evidence. It proposes that one of the pilots operated the switches in an unconscious action called an "action slip". This is a rote action that we do without conscious thought when we're distracted: we mean to do something, and then we get our signals crossed and do something else. To learn more, search for "action slip" or "cerebellum" on this thread; I hope paulross adds the keyword to the next build of his excellent index at https://paulross.github.io/pprune-th...171/index.html .
How would this scenario play out?
We don't have enough evidence to pin down the exact sequence, so there are some assumptions here that I hope you find plausible. (And obviously it's not the only scenario that fits the evidence.) We especially do not know who did what and why, so that is all guesswork on my part. The times are taken from the preliminary report. The report places the verbal exchange among the pilots where I put it.
———
8:08:39 The 787 becomes airborne. The F/O is pilot flying (PF), with both hands on the yoke. The Captain is PNF (not flying).
8:08:42 The PNF unconsciously flips both fuel switches to CUT OFF, one after the other. This is a rote action performed after each flight, or as training captain in the simulator.
The action cuts power to the engines; they stop delivering thrust almost immediately, and the turbines start slowing down.
The 787 systems disconnect the electrical generators in advance of them failing. The right side
The PF feels the cessation of thrust. He looks at the display to see an ENGINES SHUT OFF message. He assumes the PNF shut them off, and asks him why he shut them off. This is the lowest "probe" level on the PACE assertiveness scale; see e.g. https://psychsafety.com/pace-graded-assertiveness/ or search for "probe alert" on pprune if you wish to know more. The highest level of assertiveness, E for "emergency", would have the F/O put the switches back himself immediately, but that would have required a high degree of confidence in the face of the older Captain that may have been difficult to achieve.
Since the action was unconscious, the PNF replies that he did not do that.
8:08:47 The RAT starts delivering hydraulic power, the engines decelerate past idle.
The PNF realizes that engine power is in fact cut. Eventually he checks the switches he thinks he did not touch, sees the engine 1 switch first and flips it back to RUN at 8:08:52. He then thinks to check the second switch and flips it up at 8:08:56.
The accident sequence ensues.
There's really not much the PNF can do at this point. At 8:09:05, he transmits a MAYDAY.
———
Obviously there are variations to this, for example it could have been the PF who put the fuel switches back. (In the above scenario, the PF is focused on flying—aviate!—and never turns his head to see the switches.) My goal was simply to set out a possible sequence, to see whether it feels plausible. Remember, as you see other scenarios put forth, that any issues a person could wrestle with would also be distracting. While both pilots would be very focused during the takeoff run, the moment the aircraft lifted off, the PNF could well have mentally relaxed a little, opening an opportunity for the action slip.
Thoughts?
Edit: I got the roles mixed up; in a fixed scenario, either the Captain was the PF (and may have set the switches to cutoff), or flight control changed over at the power failure.
Last edited by Musician; 13th July 2025 at 08:03 .
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July 13, 2025, 07:31:00 GMT
permalink Post: 11921085
If we assume that the report is factual, as there is no good reason to think otherwise, then the aircraft was serviceable and there were no faults, messages or warnings right up to the point the FCSs were moved to cutoff, as they would have been detailed in the report. The only unresolved question is why was this done?
Putting deliberate action to one side, if the FO was the PF in manual flight, as SOP the captain as PM would be making any configuration changes, MCP selections or switch movements. We know that the captain was a trainer and as such, it is likely that he was used to running details both from the instructor station and either seat. Given the constraints on simulator time and ever-increasing syllabi it is not uncommon for trainers to physically reset the sim to save time and that includes moving critical controls without diagnosis or confirmation in ways inappropriate for the phase of flight, even if frozen. It is likely that if you were doing a lot of training, you would become more practiced at this than the SOP multi-crew interactive method and unknowingly build a semi-autonomous routine in your mind that allowed these type of actions as there was no jeopardy. Normal line pilots are only trained/practiced/checked on the correct way of doing these.
I\x92m not saying that this is what happened, just offering one possibility as to how a competent crew could end up in a disastrous scenario and experience post-decision dissonance over what had just transpired.
Putting deliberate action to one side, if the FO was the PF in manual flight, as SOP the captain as PM would be making any configuration changes, MCP selections or switch movements. We know that the captain was a trainer and as such, it is likely that he was used to running details both from the instructor station and either seat. Given the constraints on simulator time and ever-increasing syllabi it is not uncommon for trainers to physically reset the sim to save time and that includes moving critical controls without diagnosis or confirmation in ways inappropriate for the phase of flight, even if frozen. It is likely that if you were doing a lot of training, you would become more practiced at this than the SOP multi-crew interactive method and unknowingly build a semi-autonomous routine in your mind that allowed these type of actions as there was no jeopardy. Normal line pilots are only trained/practiced/checked on the correct way of doing these.
I\x92m not saying that this is what happened, just offering one possibility as to how a competent crew could end up in a disastrous scenario and experience post-decision dissonance over what had just transpired.
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July 13, 2025, 07:32:00 GMT
permalink Post: 11921086
Rather confusingly, AvHerald carries this today
"On Jul 12th 2025 (UTC) India's media report that the investigation is NOT focussing on a human action causing the fuel switches to appear in the CUTOFF position, but on a system failure."
I have no idea what provenance to attach to that!
"On Jul 12th 2025 (UTC) India's media report that the investigation is NOT focussing on a human action causing the fuel switches to appear in the CUTOFF position, but on a system failure."
I have no idea what provenance to attach to that!
Some Boeing SB's describe circuit board failures triggering all sorts of unexpected / unpredictable failures
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July 13, 2025, 07:36:00 GMT
permalink Post: 11921087
What is an action slip?
There's a possible scenario we're discussing here that fits all of the available evidence. It proposes that one of the pilots operated the switches in an unconscious action called an "action slip". This is a rote action that we do without conscious thought when we're distracted: we mean to do something, and then we get our signals crossed and do something else. To learn more, search for "action slip" or "cerebellum" on this thread; I hope paulross adds the keyword to the next build of his excellent index at https://paulross.github.io/pprune-th...171/index.html .
How would this scenario play out?
We don't have enough evidence to pin down the exact sequence, so there are some assumptions here that I hope you find plausible. (And obviously it's not the only scenario that fits the evidence.) We especially do not know who did what and why, so that is all guesswork on my part. The times are taken from the preliminary report. The report places the verbal exchange among the pilots where I put it.
\x97\x97\x97
8:08:39 The 787 becomes airborne. The F/O is pilot flying (PF), with both hands on the yoke. The Captain is PNF (not flying).
8:08:42 The PNF unconsciously flicks both fuel switches to CUT OFF, one after the other. This is a rote action performed after each flight, or as training captain in the simulator.
The action cuts power to the engines; they stop delivering thrust almost immediately, and the turbines start slowing down.
The 787 systems disconnect the electrical generators in advance of them failing. The right side (Captain's side) of the cockpit loses power to most instruments. With all 4 generators offline, the RAT deploys to provide emergency power.
The PF feels the cessation of thrust. He looks at the display to see an ENGINES SHUT OFF message. He assumes the PNF shut them off, and asks him why he shut them off. This is the lowest "probe" level on the PACE assertiveness scale; see e.g. https://psychsafety.com/pace-graded-assertiveness/ or search for "probe alert" on pprune if you wish to know more. The highest level of assertiveness, E for "emergency", would have the F/O put the switches back himself immediately, but that would have required a high degree of confidence in the face of the older Captain that may have been difficult to achieve.
Since the action was unconscious, the PNF replies that he did not do that.
8:08:47 The RAT starts delivering hydraulic power, the engines decelerate past idle.
The PNF realizes that engine power is in fact cut. Eventually he checks the switches he thinks he did not touch, sees the engine 1 switch first and flips it back to RUN at 8:08:52. He then thinks to check the second switch and flips it up at 8:08:56.
The accident sequence ensues.
There's really not much the PNF can do at this point. At 8:09:05, he transmits a MAYDAY.
\x97\x97\x97
Obviously there are variations to this, for example it could have been the PF who put the fuel switches back. (In the above scenario, the PF is focused on flying\x97aviate!\x97and never turns his head to see the switches.) My goal was simply to set out a possible sequence, to see whether it feels plausible. Remember, as you see other scenarios put forth, that any issues a person could wrestle with would also be distracting. While both pilots would be very focused during the takeoff run, the moment the aircraft lifted off, the PNF could well have mentally relaxed a little, opening an opportunity for the action slip.
Thoughts?
There's a possible scenario we're discussing here that fits all of the available evidence. It proposes that one of the pilots operated the switches in an unconscious action called an "action slip". This is a rote action that we do without conscious thought when we're distracted: we mean to do something, and then we get our signals crossed and do something else. To learn more, search for "action slip" or "cerebellum" on this thread; I hope paulross adds the keyword to the next build of his excellent index at https://paulross.github.io/pprune-th...171/index.html .
How would this scenario play out?
We don't have enough evidence to pin down the exact sequence, so there are some assumptions here that I hope you find plausible. (And obviously it's not the only scenario that fits the evidence.) We especially do not know who did what and why, so that is all guesswork on my part. The times are taken from the preliminary report. The report places the verbal exchange among the pilots where I put it.
\x97\x97\x97
8:08:39 The 787 becomes airborne. The F/O is pilot flying (PF), with both hands on the yoke. The Captain is PNF (not flying).
8:08:42 The PNF unconsciously flicks both fuel switches to CUT OFF, one after the other. This is a rote action performed after each flight, or as training captain in the simulator.
The action cuts power to the engines; they stop delivering thrust almost immediately, and the turbines start slowing down.
The 787 systems disconnect the electrical generators in advance of them failing. The right side (Captain's side) of the cockpit loses power to most instruments. With all 4 generators offline, the RAT deploys to provide emergency power.
The PF feels the cessation of thrust. He looks at the display to see an ENGINES SHUT OFF message. He assumes the PNF shut them off, and asks him why he shut them off. This is the lowest "probe" level on the PACE assertiveness scale; see e.g. https://psychsafety.com/pace-graded-assertiveness/ or search for "probe alert" on pprune if you wish to know more. The highest level of assertiveness, E for "emergency", would have the F/O put the switches back himself immediately, but that would have required a high degree of confidence in the face of the older Captain that may have been difficult to achieve.
Since the action was unconscious, the PNF replies that he did not do that.
8:08:47 The RAT starts delivering hydraulic power, the engines decelerate past idle.
The PNF realizes that engine power is in fact cut. Eventually he checks the switches he thinks he did not touch, sees the engine 1 switch first and flips it back to RUN at 8:08:52. He then thinks to check the second switch and flips it up at 8:08:56.
The accident sequence ensues.
There's really not much the PNF can do at this point. At 8:09:05, he transmits a MAYDAY.
\x97\x97\x97
Obviously there are variations to this, for example it could have been the PF who put the fuel switches back. (In the above scenario, the PF is focused on flying\x97aviate!\x97and never turns his head to see the switches.) My goal was simply to set out a possible sequence, to see whether it feels plausible. Remember, as you see other scenarios put forth, that any issues a person could wrestle with would also be distracting. While both pilots would be very focused during the takeoff run, the moment the aircraft lifted off, the PNF could well have mentally relaxed a little, opening an opportunity for the action slip.
Thoughts?
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July 13, 2025, 07:41:00 GMT
permalink Post: 11921093
What is an action slip?
There's a possible scenario we're discussing here that fits all of the available evidence. It proposes that one of the pilots operated the switches in an unconscious action called an "action slip". This is a rote action that we do without conscious thought when we're distracted: we mean to do something, and then we get our signals crossed and do something else. To learn more, search for "action slip" or "cerebellum" on this thread; I hope paulross adds the keyword to the next build of his excellent index at https://paulross.github.io/pprune-th...171/index.html .
How would this scenario play out?
We don't have enough evidence to pin down the exact sequence, so there are some assumptions here that I hope you find plausible. (And obviously it's not the only scenario that fits the evidence.) We especially do not know who did what and why, so that is all guesswork on my part. The times are taken from the preliminary report. The report places the verbal exchange among the pilots where I put it.
———
8:08:39 The 787 becomes airborne. The F/O is pilot flying (PF), with both hands on the yoke. The Captain is PNF (not flying).
8:08:42 The PNF unconsciously flicks both fuel switches to CUT OFF, one after the other. This is a rote action performed after each flight, or as training captain in the simulator.
The action cuts power to the engines; they stop delivering thrust almost immediately, and the turbines start slowing down.
The 787 systems disconnect the electrical generators in advance of them failing. The right side (Captain's side) of the cockpit loses power to most instruments. With all 4 generators offline, the RAT deploys to provide emergency power.
The PF feels the cessation of thrust. He looks at the display to see an ENGINES SHUT OFF message. He assumes the PNF shut them off, and asks him why he shut them off. This is the lowest "probe" level on the PACE assertiveness scale; see e.g. https://psychsafety.com/pace-graded-assertiveness/ or search for "probe alert" on pprune if you wish to know more. The highest level of assertiveness, E for "emergency", would have the F/O put the switches back himself immediately, but that would have required a high degree of confidence in the face of the older Captain that may have been difficult to achieve.
Since the action was unconscious, the PNF replies that he did not do that.
8:08:47 The RAT starts delivering hydraulic power, the engines decelerate past idle.
The PNF realizes that engine power is in fact cut. Eventually he checks the switches he thinks he did not touch, sees the engine 1 switch first and flips it back to RUN at 8:08:52. He then thinks to check the second switch and flips it up at 8:08:56.
The accident sequence ensues.
There's really not much the PNF can do at this point. At 8:09:05, he transmits a MAYDAY.
———
Obviously there are variations to this, for example it could have been the PF who put the fuel switches back. (In the above scenario, the PF is focused on flying—aviate!—and never turns his head to see the switches.) My goal was simply to set out a possible sequence, to see whether it feels plausible. Remember, as you see other scenarios put forth, that any issues a person could wrestle with would also be distracting. While both pilots would be very focused during the takeoff run, the moment the aircraft lifted off, the PNF could well have mentally relaxed a little, opening an opportunity for the action slip.
Thoughts?
There's a possible scenario we're discussing here that fits all of the available evidence. It proposes that one of the pilots operated the switches in an unconscious action called an "action slip". This is a rote action that we do without conscious thought when we're distracted: we mean to do something, and then we get our signals crossed and do something else. To learn more, search for "action slip" or "cerebellum" on this thread; I hope paulross adds the keyword to the next build of his excellent index at https://paulross.github.io/pprune-th...171/index.html .
How would this scenario play out?
We don't have enough evidence to pin down the exact sequence, so there are some assumptions here that I hope you find plausible. (And obviously it's not the only scenario that fits the evidence.) We especially do not know who did what and why, so that is all guesswork on my part. The times are taken from the preliminary report. The report places the verbal exchange among the pilots where I put it.
———
8:08:39 The 787 becomes airborne. The F/O is pilot flying (PF), with both hands on the yoke. The Captain is PNF (not flying).
8:08:42 The PNF unconsciously flicks both fuel switches to CUT OFF, one after the other. This is a rote action performed after each flight, or as training captain in the simulator.
The action cuts power to the engines; they stop delivering thrust almost immediately, and the turbines start slowing down.
The 787 systems disconnect the electrical generators in advance of them failing. The right side (Captain's side) of the cockpit loses power to most instruments. With all 4 generators offline, the RAT deploys to provide emergency power.
The PF feels the cessation of thrust. He looks at the display to see an ENGINES SHUT OFF message. He assumes the PNF shut them off, and asks him why he shut them off. This is the lowest "probe" level on the PACE assertiveness scale; see e.g. https://psychsafety.com/pace-graded-assertiveness/ or search for "probe alert" on pprune if you wish to know more. The highest level of assertiveness, E for "emergency", would have the F/O put the switches back himself immediately, but that would have required a high degree of confidence in the face of the older Captain that may have been difficult to achieve.
Since the action was unconscious, the PNF replies that he did not do that.
8:08:47 The RAT starts delivering hydraulic power, the engines decelerate past idle.
The PNF realizes that engine power is in fact cut. Eventually he checks the switches he thinks he did not touch, sees the engine 1 switch first and flips it back to RUN at 8:08:52. He then thinks to check the second switch and flips it up at 8:08:56.
The accident sequence ensues.
There's really not much the PNF can do at this point. At 8:09:05, he transmits a MAYDAY.
———
Obviously there are variations to this, for example it could have been the PF who put the fuel switches back. (In the above scenario, the PF is focused on flying—aviate!—and never turns his head to see the switches.) My goal was simply to set out a possible sequence, to see whether it feels plausible. Remember, as you see other scenarios put forth, that any issues a person could wrestle with would also be distracting. While both pilots would be very focused during the takeoff run, the moment the aircraft lifted off, the PNF could well have mentally relaxed a little, opening an opportunity for the action slip.
Thoughts?
Seeing that the gear remained down after liftoff, there was CVR confusion after the event, and there was an attempt to rectify the situation…. I’m now thinking aviation is witnessing its most bizarre action-slip it’s ever seen and we’ll learn that the human automatic system is capable of making the most inappropriate and illogical responses to a given situation. I suspect fatigue and the captains sim experience of flicking switches plays a part.
As a result of this, I think we’ll see a renewed interest in slowing down actions at all times…touch a control, look at it, pause, consciously think about what you are touching before you execute it. This needs to be habitual, especially on LH fleets where fatigue inevitably plays into the operation.
We’ll also be discouraging the “insta-pilot” trend of showing how slick you are (usually on A320) where your hands flick round the flight deck at lightning speed. Even in more benign scenarios like shutdown flows etc, this isn’t a good habit.
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July 13, 2025, 07:53:00 GMT
permalink Post: 11921100
A lot of \xabflipping\xbb and \xabflicking\xbb of fuel switches going on. You don\x92t flick or flip these switches. They require a deliberate movement.
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July 13, 2025, 08:08:00 GMT
permalink Post: 11921110
A statement that completely underestimates the human subconscious system. You need a deliberate movement to raise the gear or drop the flaps too…I’d say nearly every operator has instances of pilots accidentally doing one instead of the other. There will be people saying that there is no way you can have such an extreme action slip but I don’t think we should ever underestimate the power of the human to do the most random things, even if it is one-in-a-million event.
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July 13, 2025, 08:16:00 GMT
permalink Post: 11921117
A statement that completely underestimates the human subconscious system. You need a deliberate movement to raise the gear or drop the flaps too\x85I\x92d say nearly every operator has instances of pilots accidentally doing one instead of the other. There will be people saying that there is no way you can have such an extreme action slip but I don\x92t think we should ever underestimate the power of the human to do the most random things, even if it is one-in-a-million event.
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July 13, 2025, 08:16:00 GMT
permalink Post: 11921118
Action slip seems highly unlikely to me. Even if one cutoff switch was moved in response to a gear up request I can\x92t believe anyone would then move a second switch, one second later.
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