June 21, 2025, 12:49:00 GMT
permalink Post: 11907719
There was no sign of asymmetric thrust failure, but rather, nearly total loss of thrust just after rotation. Something has caused a catastrophic electric failure that has impacted the air /ground logic functions. There are signs that this event is unique, although there have been cases in the past where the logic has failed and the aircraft no longer knows if it's airborne or not. The crew were probably faced with something they weren't trained for and overwhelmed them. There would have been not enough time to troubleshoot this.
In the scenario you are considering, it's clear that the air/ground state would be wrongly "understood" by the TCMA function. But we don't have, AFAIK , a credible theory for how that might happen. Surely it would have to result from either incorrect signals from the relevant sensors or a failure of the related logic in the FADEC TCMA function, or a combination of those. Indeed, I don't think we yet know exactly which sensor readings that logic depends on or how those readings are fed to the FADEC. Does your speculation include any thoughts about this?
Also, the FADEC TCMA function has to "believe" that the engine is operating at high power and not responding to thrust lever operation. In your proposed scenario, is this also a logic failure \x97 in both FADECs? Or false inputs from both TLs? Or are both engines actually operating at higher than commanded power levels?
Or do I misunderstand your post?
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): FADEC
June 21, 2025, 17:05:00 GMT
permalink Post: 11907908
tdracer was detailing the inputs to TCMA on a 74 and has said repeatedly that he doesn't know the details of that function on 787s. I'm sure of that because I misread his original post and based a post of mine on the misreading. The inputs he described were multiple WoW switches and multiple RAs, with inputs from each group required to determine that the aircraft is on the ground to enable TCMA-initiated shutdown. It seems likely that the 787 is similar, but that hasn't been established here. I've been looking but haven't found the details yet.
Last edited by OldnGrounded; 21st June 2025 at 17:06 . Reason: Clarification
Subjects: None
June 22, 2025, 01:35:00 GMT
permalink Post: 11908213
Perhaps my earlier post was incredible and that's what prompted the SLF's question.
Let us assume a simple, hypothetical WoW sensor arrangement: One sensor per main landing gear.
One of those sensors is indicating weight OFF wheels and the other is indicating weight ON wheels. What does the TCMA in each engine interpret that ostensibly contradictory sensor information to mean? (Note: For the time being, ignore the question whether the information is erroneous. It may be true.)
Are both engine TCMA's in the 'in the air' state, are both 'on the ground', or is one 'on the ground' and the other 'in the air'?
Given the purpose of the TCMA, I would have thought that any 'doubt' in this case would be resolved in favour of the 'on ground' state for both TCMAs.
But maybe it's the other way around. Maybe any 'doubt' would be resolved in favour of both TCMA's being in the 'in the air' state.
I have difficulty in envisaging any advantage in the TCMA system being designed such that one engine's TCMA is in the 'in the air' state and the engine's 'on the ground'.
Whichever the design and outcome, there will be benefits and there will be risks.
Let us assume a simple, hypothetical WoW sensor arrangement: One sensor per main landing gear.
One of those sensors is indicating weight OFF wheels and the other is indicating weight ON wheels. What does the TCMA in each engine interpret that ostensibly contradictory sensor information to mean? (Note: For the time being, ignore the question whether the information is erroneous. It may be true.)
Are both engine TCMA's in the 'in the air' state, are both 'on the ground', or is one 'on the ground' and the other 'in the air'?
Given the purpose of the TCMA, I would have thought that any 'doubt' in this case would be resolved in favour of the 'on ground' state for both TCMAs.
But maybe it's the other way around. Maybe any 'doubt' would be resolved in favour of both TCMA's being in the 'in the air' state.
I have difficulty in envisaging any advantage in the TCMA system being designed such that one engine's TCMA is in the 'in the air' state and the engine's 'on the ground'.
Whichever the design and outcome, there will be benefits and there will be risks.
Subjects: None
June 22, 2025, 14:04:00 GMT
permalink Post: 11908564
Subjects: None
June 22, 2025, 14:51:00 GMT
permalink Post: 11908593
I do SMD rework and failure analysis on automotive control devices and if there would be so much at stake, even if I would be a known expert, I would ask for something to 'play with' or in less offending words: test the equipment, process and success rate on something from the 'scrapyard'. Experience would prevent me from starting with the FDR from the flight.
Maybe they officially need a week to decide where to put it while exactly this is happening, they are doing a dry-run.
Maybe they officially need a week to decide where to put it while exactly this is happening, they are doing a dry-run.
Also, please note that I have no comment on whatever decisions may have been made or be pending, in this accident, about where to download and analyze the data. Well, no comment except that I see no reason to question the Indian authorities' ability to make those decisions appropriately and with adequate knowledge and expertise.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): FDR
July 11, 2025, 23:01:00 GMT
permalink Post: 11919961
I don't see people arguing that a pilot didn't move the switches. I see people offering various alternative possibilities. I do see posters, and mods, insisting that we not suggest deliberate operation of the switches with evil intent without evidence and I think that's an excellent idea.
Also: The preliminary report does not include any specific language for the question and answer about moving the engine control switches . Please, let's stop the imaginary quoting and responses to it.
Also: The preliminary report does not include any specific language for the question and answer about moving the engine control switches . Please, let's stop the imaginary quoting and responses to it.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Preliminary Report Thread Moderation
July 11, 2025, 23:34:00 GMT
permalink Post: 11920000
Yup, because even 20K-hour Sully is human, just like all the rest of us. A damned impressive human, of course. I'm just an easily-confused engineer, but even the most awesome sky gods here (and I am in awe of more than a few of them) cannot know what another pilot, or even they themselves, would do or how long it might take in a situation like the one in this accident.
Subjects: None
July 13, 2025, 14:48:00 GMT
permalink Post: 11921368
At this point, I agree that intentional operation of the FCS switches is the most likely cause of the shutdown. But that doesn't mean that we know or can know what the intent of the intentional action was. And I don't think we have any compelling evidence that the intent was to crash the aircraft and kill everyone aboard.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Relight
July 13, 2025, 16:23:00 GMT
permalink Post: 11921420
I would suggest everyone that wants to analyze the likelihood of particular actions on the part of the crew, whether referring to "muscle memory" or "brain farts" or whatever, simply add the phrase "
during the initial climb
" to their thoughts and see how that sounds. Without callouts for raising the gear and other than sleepwalking, what explanation is there for flipping the fuel cutoffs down in sequence? And further, doing so precisely in the time window where it was most likely to make the situation unrecoverable?
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Muscle Memory
July 13, 2025, 19:06:00 GMT
permalink Post: 11921543
"This" apparently meaning that the Captain deliberately and with evil intent moved the FCS switches to CUTOFF and then accused the FO of doing it.
Of course we can't accept it as fact. There's no credible evidence indicating that it happened, much less dispositive evidence.
Of course we can't accept it as fact. There's no credible evidence indicating that it happened, much less dispositive evidence.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): RUN/CUTOFF
July 13, 2025, 19:45:00 GMT
permalink Post: 11921577
Subjects: None
July 13, 2025, 19:50:00 GMT
permalink Post: 11921583
Is there? Is there evidence for the scenario that you have endorsed, that the Captain deliberately, intending to crash the airplane, moved the fuel control switches to CUTOFF and then accused the FO of doing that? What is that evidence?
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Fuel (All) Fuel Cutoff Switches RUN/CUTOFF
July 13, 2025, 20:21:00 GMT
permalink Post: 11921608
Some human in that flight deck moved both fuel switches to cutoff, physically moved them, one after the other. Another human, possibly either human in that flight deck then questioned verbally why they did that. This is factual and proven evidence as per the official report. Why are we not focusing on the who and why!?
Not sure how much more evidence you need to start a discussion.
We as operators are trying to put ourselves in that situation and describe likely outcomes based on present experiences. The most likely event is the PM orchestrating this, the Captain in this case. This however is up for debate\x85 the debate we should be having\x85 not APU doors.
Not sure how much more evidence you need to start a discussion.
We as operators are trying to put ourselves in that situation and describe likely outcomes based on present experiences. The most likely event is the PM orchestrating this, the Captain in this case. This however is up for debate\x85 the debate we should be having\x85 not APU doors.
I certainly don't need more evidence than we have for discussion. I just think a lot more evidence is necessary to conclude that either crew member on that flight deliberately killed the engines intending to crash the jet and, for some reason, accused the other of doing so. Indeed, I don't think we have any actual evidence for that. We simply have a set of circumstances that make that one of only a few possibilities we can reasonably imagine. Discussing it as a possibility is reasonable (although I don't think we can get anywhere on that path without evidence), but claiming that possibility as the one, the truth, what really happened, is not reasonable, not justified by the available evidence. And making unjustified claims that amount to accusing a pilot of mass murder, in a forum that citizens and journalists from around the world always turn to for information in the wake of a major airliner crash, seems like a very bad idea to me.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): APU Fuel (All) Fuel Cutoff Switches Relight
July 14, 2025, 00:08:00 GMT
permalink Post: 11921795
The two fuel cutoff switches were put in the OFF position. If you have ever used those switches yourself, you will know that it can not be accidental. A deliberate action from one of the pilots is BY FAR the most plausible (or only) explanation. I feel very sorry for the innocent pilot in the cockpit and the hundreds of other victims. Having passed many medical examinations, I can assure you that psychological testing is not part of the periodic medicals.
It does appear to me that you're NOT open to evidence if you continue to deny that a deliberate pilot action is not plausible.
Please enlighten me about how much time you have spent in an airline cockpit... Judging by what you contribute I suspect it will not be much.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Fuel (All) Fuel Cutoff Fuel Cutoff Switches RUN/CUTOFF
July 14, 2025, 11:38:00 GMT
permalink Post: 11922109
. . . His records have been handed to investigators,
whose initial report said their focus was on the actions of the pilots rather than a technical fault with the plane.
The Airline Pilots’ Association of India said it rejected the “tone and direction” of the inquiry.
The preliminary report doesn't say that.
Last edited by T28B; 14th July 2025 at 12:07 . Reason: fixed brackets
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Preliminary Report
July 14, 2025, 11:48:00 GMT
permalink Post: 11922119
We don't have evidence sufficient to reach that conclusion in either case. Maybe such evidence will emerge in the Air India crash investigation. Conceivably, investigators already have it (although, if they do, it should have been cited in the preliminary report), but we don't have it. If that's what happened in MH370, it seems pretty unlikely, at this point, that it's going to emerge.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): CCTV Preliminary Report
July 14, 2025, 16:41:00 GMT
permalink Post: 11922355
Why do you think it is a "fact that nobody apparently announced 'engine failure'?" That was not included in the preliminary report or, as far as I know, in any other credible reporting here or elsewhere.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Engine Failure (All) Fuel (All) Fuel Cutoff Switches Preliminary Report
July 15, 2025, 18:37:00 GMT
permalink Post: 11923165
We know with reasonable (although not perfect) certainty that the fuel control switches were placed in CUTOFF almost immediately after rotation and were later moved back to RUN. We do not know who did that or why it was done and we don't have nearly enough information to answer those questions with any confidence.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Fuel (All) Fuel Cutoff Switches Preliminary Report RUN/CUTOFF
July 15, 2025, 18:43:00 GMT
permalink Post: 11923170
Not all, of course, but I absolutely do think that most investigators in roles such as the ones we are discussing are professionals who would and do resist improper influence. Immune? No, none of us are. Guarded against? Yes, that's what professionals with integrity do every hour of every working day.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Switch Guards
July 15, 2025, 18:47:00 GMT
permalink Post: 11923174
Again I'm not even saying its suicide, you prob may only know if you heard the CVR and even then their could be a question. What I'm saying is anyone downplaying that as an option because it's "rare" but then goes down the path of concocting some crazy failure scenario . . .
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): CVR