July 12, 2025, 11:32:00 GMT
permalink Post: 11920533
Originally Posted by
Uplinker
This might have been discussed but as has been suggested upthread; a possible scenario is that at some point, PIC took their hands off the thrust levers and/or placed them in a guarding position behind the thrust levers at their base - but by doing so unfortunately nudged the Fuel cut-off switches to 'Off' - perhaps 'helped' by there either being incorrectly fitted locking mechanisms or worn locking mechanisms ?
Originally Posted by
Uplinker
On this flight, the relative drop in noise and calm that follows the landing gear doors closing after the gear retracts during the initial climb, might have caused an action slip by PIC to perform the engine shut-down procedure used when parking on stand.
Mods, if you don't lock the thread, I'm going back to Facebook!
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July 12, 2025, 11:39:00 GMT
permalink Post: 11920545
nachtmusak
the RAT can be deployed manually, and I believe a pilot did that here before power was lost.
The timing of data loss seemingly lining up with the first cutoff switch being flipped back to RUN seems a little too coincidental to me, but again hopefully someone with relevant knowledge has a mundane explanation for this.
On top of that I feel like people are overestimating how long ten seconds actually is, especially considering some of those seconds are reported to have been taken up by confused dialogue (that isn't even reported in its entirety). I thought it was common wisdom that accidents are never down to one thing; it would be light-years from being the first time that suboptimal crew response turned a maybe-recoverable error into a definite disaster without an ounce of malice in the mix.
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July 12, 2025, 11:41:00 GMT
permalink Post: 11920549
The gear were never retracted on this flight, so the action being caused by gear up quietness is not feasible.
Action slip in general... technically possible, but there should still be no actions being taken other than gear up (and probably still a bit early for that).
Engines off instead of gear up is one hell of an action slip.
Action slip in general... technically possible, but there should still be no actions being taken other than gear up (and probably still a bit early for that).
Engines off instead of gear up is one hell of an action slip.
Ah, OK, noted re the gear. But there must have been some other distraction that led to an action-slip. For example, why wasn't the gear retracted ? - it is a very clear sequence: " V1......Rotate......positive climb......gear up....." So something else must have happened to distract both pilots.
Perhaps the brakes were hot, so maybe they deliberately delayed bringing the gear up to let them cool first - (an occasionally needed but standard procedure). This uncommon sequence in turn might possibly have led to an action slip.
But action-slips are exactly that. A valid action applied to completely the wrong situation. E.g putting the milk in the bin or the microwave instead of back in the fridge.
Highly unlikely, I know, but..............
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July 12, 2025, 11:52:00 GMT
permalink Post: 11920558
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July 12, 2025, 11:59:00 GMT
permalink Post: 11920565
Regardless of what actually happened in that cockpit, reasoning like this seems completely backwards to me. Since when do humans reliably, instantly recognise that they've just made a mistake? If they were
that
attuned to their actions they're almost certainly attuned enough to
not
make the mistake in the first place, especially if we're talking about an action slip. I've e.g. absentmindedly added salt to my tea instead of sugar and I certainly didn't immediately realise that I'd done that - in fact it took a good few seconds even after sipping and spitting it out for my brain to catch up to what must have happened. Even if an observer had pointed out to me before drinking it that my tea had salt in it, I would just have been confused because
obviously
I wouldn't do something that silly (spoiler alert: I did)..
When they rip their hand away from the hot stove they’ve just touched.
Had this been a silly mistake, it was one with immediate, severe consequences, not something like discovering a mistake you made some time ago. As for response to the mistake, see below
On top of that I feel like people are overestimating how long ten seconds actually is, especially considering some of those seconds are reported to have been taken up by confused dialogue (that isn't even reported in its entirety). I thought it was common wisdom that accidents are never down to one thing; it would be light-years from being the first time that suboptimal crew response turned a maybe-recoverable error into a definite disaster without an ounce of malice in the mix.
Again, the situation isn’t a surprise to you, you know what just happened.
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July 12, 2025, 18:47:00 GMT
permalink Post: 11920745
I think we need to be really careful about how we think about human factors.
To all of you who have talked about ‘muscle memory’ or ‘brain farts’ may I refer you all to post No. 183 by MaybeItIs. In it, he writes about the interactions between the cerebellum and the cerebrum – in effect, we have two brains; the cerebrum being the ‘conscious thinking part’ and the cerebellum being the ‘unconscious automatic part’ of our brains.
All of us have done very strange inexplicable things at some time or another in our lives, you only have to read about human factors to know how common such things are – even by highly trained flight crews . I know I have made mistakes like these, and I ask you all to examine your own lives and acknowledge that you may have done the same.
In my own experience, when I was a very new co-pilot, I was involved in a very nasty incident in a VC10 in which we all did inappropriate things, with the best of intentions . We very nearly ended up crashing. After that experience, I began to read books on psychology, brain structure and human behaviour. You will be surprised how easy it is to do the wrong thing and then, afterwards, to wonder why.
Later, I spent much of my career as a training pilot and as a training manager. Despite all the safeguards built in by designers and manufacturers, despite all the safeguards included in our crew procedures, and despite all the training we undergo during our careers, we are all still vulnerable to error, including the so-called ‘sky-gods’.
James Reason wrote about the Swiss Cheese model. Sometimes, one of the holes in the cheese can be our own totally improbable actions. What MaybeItIs has written in his post may help to explain such seemingly inexplicable events.
We all need to have some humility – There but for the grace of God go I.
To all of you who have talked about ‘muscle memory’ or ‘brain farts’ may I refer you all to post No. 183 by MaybeItIs. In it, he writes about the interactions between the cerebellum and the cerebrum – in effect, we have two brains; the cerebrum being the ‘conscious thinking part’ and the cerebellum being the ‘unconscious automatic part’ of our brains.
All of us have done very strange inexplicable things at some time or another in our lives, you only have to read about human factors to know how common such things are – even by highly trained flight crews . I know I have made mistakes like these, and I ask you all to examine your own lives and acknowledge that you may have done the same.
In my own experience, when I was a very new co-pilot, I was involved in a very nasty incident in a VC10 in which we all did inappropriate things, with the best of intentions . We very nearly ended up crashing. After that experience, I began to read books on psychology, brain structure and human behaviour. You will be surprised how easy it is to do the wrong thing and then, afterwards, to wonder why.
Later, I spent much of my career as a training pilot and as a training manager. Despite all the safeguards built in by designers and manufacturers, despite all the safeguards included in our crew procedures, and despite all the training we undergo during our careers, we are all still vulnerable to error, including the so-called ‘sky-gods’.
James Reason wrote about the Swiss Cheese model. Sometimes, one of the holes in the cheese can be our own totally improbable actions. What MaybeItIs has written in his post may help to explain such seemingly inexplicable events.
We all need to have some humility – There but for the grace of God go I.
Last edited by Bergerie1; 13th July 2025 at 04:04 . Reason: Changed reference to Post No. 183
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July 12, 2025, 19:21:00 GMT
permalink Post: 11920769
I don\x92t know if the FDR measures the switch position or the electrical signal. The latter is probably more likely, although there has been much discussion around potential scenarios involving accidental switch movement as well as possible causes of electrical glitches. Let\x92s assume that the switches were actually moved, and ignoring the \x93bad faith\x94 scenario, we need a situation that encompasses the switches being moved to Cutoff by one pilot, this action being queried by the other pilot and denied by the pilot who moved the switches.
For consideration, here is a possible scenario that hasn\x92t been mentioned yet and encompasses the frailty of human performance. The report mentions that the flight crew on the immediately prior flight had written up a "STAB POS XDCR" status message, and that troubleshooting was carried out. I wonder if the scenario could be that the accident crew received a Stabiliser EICAS message on or around take-off and the Capt (who was PM) decided to action the first checklist item immediately from memory, by intending to move the Stab switches to Cutoff but moving the fuel switches instead. As in all modern Boeings, the Stabiliser Cutoff switches are immediately next to the Fuel Cutoff switches and operate in the same sense (i.e. down for Cutoff). They are guarded and never normally moved but, with an intent to move the stab switches, \x93muscle memory\x94 (cerebellum activation if you prefer) may have taken the Captain\x92s hand to the Fuel switches, which are operated on every flight. The FO (who is PF) is manually flying at this stage sees and queries it. The Capt denies it, as he doesn\x92t realise what he has done (confirmation bias perhaps). After a few seconds, the terrible mistake is realised, and the fuel switches are moved back to run, but sadly too late and the Capt makes a Mayday call.
Perhaps a bit of a stretch but not as much of a stretch as many of the other scenarios in this thread. I think it is a real possibility. Sadly, the only other explanation that I can see is the deliberate \x93bad faith\x94 scenario, which we would all hope is incorrect.
Fly Safe
PJ88
For consideration, here is a possible scenario that hasn\x92t been mentioned yet and encompasses the frailty of human performance. The report mentions that the flight crew on the immediately prior flight had written up a "STAB POS XDCR" status message, and that troubleshooting was carried out. I wonder if the scenario could be that the accident crew received a Stabiliser EICAS message on or around take-off and the Capt (who was PM) decided to action the first checklist item immediately from memory, by intending to move the Stab switches to Cutoff but moving the fuel switches instead. As in all modern Boeings, the Stabiliser Cutoff switches are immediately next to the Fuel Cutoff switches and operate in the same sense (i.e. down for Cutoff). They are guarded and never normally moved but, with an intent to move the stab switches, \x93muscle memory\x94 (cerebellum activation if you prefer) may have taken the Captain\x92s hand to the Fuel switches, which are operated on every flight. The FO (who is PF) is manually flying at this stage sees and queries it. The Capt denies it, as he doesn\x92t realise what he has done (confirmation bias perhaps). After a few seconds, the terrible mistake is realised, and the fuel switches are moved back to run, but sadly too late and the Capt makes a Mayday call.
Perhaps a bit of a stretch but not as much of a stretch as many of the other scenarios in this thread. I think it is a real possibility. Sadly, the only other explanation that I can see is the deliberate \x93bad faith\x94 scenario, which we would all hope is incorrect.
Fly Safe
PJ88
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July 12, 2025, 21:31:00 GMT
permalink Post: 11920849
First, 10 seconds is not a long time. Second, I don't know where you are getting the idea that there was a 10 second gap between the pilots noticing or asking 'why did you cut off' and the switches being reset, because the report doesn't give a timestamp for either exclamation from the pilots. It may well have only been a couple of seconds between them noticing and resetting them, the report simply doesn't give that detail.
The truth will be in what was said after 'I didnt', but that's conspicuously absent from the report.
The truth will be in what was said after 'I didnt', but that's conspicuously absent from the report.
Of course deliberate pilot sabotage has occurred in the past, nobody is disputing that. But personally I'm aware of far more cases of pilot mistakes without malice as the root cause of an accident than of all the confirmed and possible cases of sabotage put together, and I'm sure that there are even more cases of the former that I've never heard about (and I don't mean pilot error in general, I'm referring to things like e.g. taking off with an improper configuration).
I think people are not actually thinking through how the situation would play out IF it was an honest mistake. Ten seconds is no time at all for either pilot to:
- notice the degrading performance (and/or warnings)
- scan the instruments and controls for the problem
- see (on their display and confirm on the pedestal) that fuel has been cut off
- ask the other pilot why they did that (because neither pilot would believe they were the one who did so - that is how action slips work)
- get a response that they did not (again, see above)
- snap out of confusion and actually do something about the situation
Pilots have reacted with far less alacrity in plenty of accidents (even in cases where the day was ultimately saved) and it was not my impression that the aviation industry accused them of criminal intent for it. Surely there is a middle ground between robotic hyper-competence and literal murder? Don't get me wrong, there is a solid chance that it turns out to have been the deliberate murder of hundreds of people. But to me at least it seems extremely uncharitable to confidently declare that that's what happened off a very loose timeline, or to paint people who are considering the possibility of a mistake as just hiding from the truth.
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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, 05:15:00 GMT
permalink Post: 11921025
May I refer you to
MaybeItIs'
post
183
and my post
351
. I think that
tdracer
has laid to rest most (if not all) of the electrical theories that have been put forward on this thread. And I find the accusations of malicious operation of the switches by one or other of the pilots to be repugnant.
This leaves the so-called 'muscle memory' and 'brain fart' theories. Those who work in the field of psychology can show quite clearly that we are all liable to seemingly inexplicable mistakes, both in normal life and in the cockpit. MaybeItIs wrote about the cerebellum and the cerebrum in his post 183, his words are very wise.
Those of us who have worked as instructors will have spent many hours embedding in our students essential habit patterns, most of which are life-savers. But, equally, habitual actions can very occasionally go wrong, despite our best intentions. I have a strong feeling that the root cause of this accident will be found to be psychological.
Some may simply try to put this down to 'pilot error' which, in a way, it is but it is not a culpable error . It is simply a result of being human.
This leaves the so-called 'muscle memory' and 'brain fart' theories. Those who work in the field of psychology can show quite clearly that we are all liable to seemingly inexplicable mistakes, both in normal life and in the cockpit. MaybeItIs wrote about the cerebellum and the cerebrum in his post 183, his words are very wise.
Those of us who have worked as instructors will have spent many hours embedding in our students essential habit patterns, most of which are life-savers. But, equally, habitual actions can very occasionally go wrong, despite our best intentions. I have a strong feeling that the root cause of this accident will be found to be psychological.
Some may simply try to put this down to 'pilot error' which, in a way, it is but it is not a culpable error . It is simply a result of being human.
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July 13, 2025, 05:23:00 GMT
permalink Post: 11921030
slats11,
Sorry, you missed the risk I'm proposing to mitigate. It's not about malfeasance.
It's about saving us from ourselves - from our "smaller brain" - not what you're probably thinking!
If you search this thread, you'll find a number of reports of highly-trained, highly qualified and normally highly competent pilots doing absolutely daft things, for no explicable reason. Even they can't explain how it happened. Here's another pretty good example, which I discussed a bit somewhere here.
https://avherald.com/h?article=48d1e3ae&opt=0
I think understanding the role of the cerebellum and what it does and how it apparently works goes a long way to explaining the seemingly otherwise inexplicable. Have a read up?
.
Sorry, you missed the risk I'm proposing to mitigate. It's not about malfeasance.
It's about saving us from ourselves - from our "smaller brain" - not what you're probably thinking!
If you search this thread, you'll find a number of reports of highly-trained, highly qualified and normally highly competent pilots doing absolutely daft things, for no explicable reason. Even they can't explain how it happened. Here's another pretty good example, which I discussed a bit somewhere here.
https://avherald.com/h?article=48d1e3ae&opt=0
I think understanding the role of the cerebellum and what it does and how it apparently works goes a long way to explaining the seemingly otherwise inexplicable. Have a read up?
.
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July 13, 2025, 06:04:00 GMT
permalink Post: 11921041
This leaves the so-called 'muscle memory' and 'brain fart' theories. Those who work in the field of psychology can show quite clearly that we are all liable to seemingly inexplicable mistakes, both in normal life and in the cockpit.
MaybeItIs
wrote about the cerebellum and the cerebrum in his post 183, his words are very wise.
It could have been an intentional, malicious act, but I think, for now, "brain fart" or "extremely inappropriate reaction to perceived anomaly" makes more sense for now.
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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, 07:36:00 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, 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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July 13, 2025, 08:21:00 GMT
permalink Post: 11921123
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July 13, 2025, 11:13:00 GMT
permalink Post: 11921238
I\x92d counter that order of likelihood by suggesting
(1) It\x92s still a likely response to ask that question if your colleague had just switched them off by action-slip.
(2) See my post above. Routine use of these switches is in one \x93event\x94\x85below OAT 40C you start both simultaneously and at shutdown you operate one straight after another.
(3) The interim report seems to leave out all information on verbal exchanges not specifically involved with a response to the abnormal situation.
Not saying you aren\x92t correct, but it doesn\x92t change the order of likelihood in my mind.
(1) It\x92s still a likely response to ask that question if your colleague had just switched them off by action-slip.
(2) See my post above. Routine use of these switches is in one \x93event\x94\x85below OAT 40C you start both simultaneously and at shutdown you operate one straight after another.
(3) The interim report seems to leave out all information on verbal exchanges not specifically involved with a response to the abnormal situation.
Not saying you aren\x92t correct, but it doesn\x92t change the order of likelihood in my mind.
By precedent in routine operations I mean: is there a single example of these switches being cut off at takeoff like this? There is precedent for the wrong engine being shut down in a fire sure, and there is perhaps precedent for mishaps with the fuel switches in other cockpit layouts - but in the case of this layout, with this model of switch or even this 'style' of switch and placement, I cannot find a single example that would come close to the level of catastrophic action slip of pulling out and setting to cutoff both switches one by one.
I think the preliminary report is supposed to present all factual information - they could have left out "why did you cutoff / I did not" - I could understand if they left out sounds that could be ambiguous, perhaps indicating a struggle but not clear enough to present as fact. However, "positive rate / gear up" followed by 2 switches instead of gear handle is completely factual and relevant information, to exclude it makes no sense.
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