June 30, 2025, 03:42:00 GMT
permalink Post: 11913342
This has also been touched upon earlier in the thread, but it rather seems the cut-off switches are in the same LRU, in close proximity, using the same connector and goes through the same wiring harness. No one was able to say whether it works purely by digital signaling, and goes through any common software, or if it is duplicated by purely direct signaling. There might be numerous failure modes of the cut-off switch design, it is obviously very, very robust and overall sound, since dual failures here have never happened, but this is alredy an outlier event.
That's a pretty big "if" but here's the patent drawing:
June 30, 2025, 06:32:00 GMT
permalink Post: 11913383
Searching the web, I found out that regulations concerning new FDR require parameter 35g "fuel cut-off lever position" to be recorded. I also found that for a 2003 event with a 757, this was recorded (as was fuel flow).
I expect that this is also true for the 787. Can anyone confirm this?
I expect that this is also true for the 787. Can anyone confirm this?
June 30, 2025, 13:59:00 GMT
permalink Post: 11913644
There are several ways that the HPSOV can close:
An EEC (engine ECU) can close the upstream Fuel Metering Valve (FMV) electronically, so the HPSOV will lose its opening pressure.
The HPSOV can be acted on by a Shutoff Solenoid Valve (which directs fuel pressure in an opposite manner to the pressure coming from the Fuel Metering Valve).
Unfortunately, the diagram I am using is truncated, and I can't see if the Shutoff Solenoid Valve is magnetically latched in its last commanded position like typical fuel shutoff valves. Nor can I see what controls it. I suspect things like the respective cockpit fire handle and fuel cutoff lever, but also EEC commands.
There is probably a copyright on the diagram, so I won't post it here. Perhaps someone can fill in the gaps for me?
July 01, 2025, 12:55:00 GMT
permalink Post: 11914255
I believe that particular bug is fixed, though it's always possible there's other issues causing a total AC loss.
Not really relevant to what you quoted though, as the scenario in question requires:
The aircraft has two engines and should be able to climb out on one, plus it dropped like a rock . 'Significantly degraded' thrust isn't really compatible with what we saw. You'd also expect the engines to recover pretty quickly as it leveled off.
The limitations at high altitude are primarily air/volatiles degassing out of the fuel. That's not going to be much of an issue at sea level, even if the engines are a bit higher up during rotation.
APU is a nice-to-have; it's on the MEL. If you lose all four generators, it's because of some major carnage in the electrical software/hardware and chances of putting the APU on line even if it's operating are very slim.
Not really relevant to what you quoted though, as the scenario in question requires:
-
Engines running on centre tank fuel during takeoff
while the aircraft is operating normally
- We don't know for certain if this is the case. It seems to be but it's not something that happens on other families.
- Then, total AC failure stopping fuel boost pumps.
- Engines suction feed from contaminated/full-of-water wing tanks.
The aircraft has two engines and should be able to climb out on one, plus it dropped like a rock . 'Significantly degraded' thrust isn't really compatible with what we saw. You'd also expect the engines to recover pretty quickly as it leveled off.
The limitations at high altitude are primarily air/volatiles degassing out of the fuel. That's not going to be much of an issue at sea level, even if the engines are a bit higher up during rotation.
APU is a nice-to-have; it's on the MEL. If you lose all four generators, it's because of some major carnage in the electrical software/hardware and chances of putting the APU on line even if it's operating are very slim.
- The specific 248-day integer overflow was patched, and before the fix was rolled out, the AD required this system to by power cycled every 120 days to prevent overflow
- The PCU software still has the functional requirement to be able to command all AC GCUs to enter failsafe mode, this means that while the initial bug was fixed, the ability for this particular software system to command the same result is still a functional part of the architecture - presumably for safety management of the AC system
- This was not the first or last "software overflow error" issue in Boeing or even in the 787
I do agree that the engine driven pumps should be able to provide fuel alone, the whole point of these pumps is to keep the plane flying within some limitations, high altitude is one of those limitations, I propose that there may be others based on the following:
- Some more knowledgable people here have proposed or countered vapour lock, fuel contamination and automatic fuel cut-off theories to various degrees - even if these are not enough on their own, loss of electrical during rotation at high temperature could combine with these in a way we have not yet considered
- Thrust is nonlinear, and while I'm not qualified to say how much loss of fuel flow or loss of thrust would be critical in this scenario we do know that it was a hot takeoff with significant weight and gear remaining down - I know others here have run sims but I don't think anyone has focused on specific thrust / fuel flow params
- While electric fuel pumps might not be physically necessary for takeoff, my final point is: why are they required for takeoff? Is it not to mitigate cavitation, fuel sloshing at rotation, or any other kind of problem that might be relevant here?
July 01, 2025, 13:08:00 GMT
permalink Post: 11914265
As an electronics and software engineer who has read the AD and related materials on the 248 day bug my understanding is that:
- The specific 248-day integer overflow was patched, and before the fix was rolled out, the AD required this system to by power cycled every 120 days to prevent overflow
- The PCU software still has the functional requirement to be able to command all AC GCUs to enter failsafe mode, this means that while the initial bug was fixed, the ability for this particular software system to command the same result is still a functional part of the architecture - presumably for safety management of the AC system
- This was not the first or last "software overflow error" issue in Boeing or even in the 787
I do agree that the engine driven pumps
should
be able to provide fuel alone, the whole point of these pumps is to keep the plane flying within
some
limitations, high altitude is one of those limitations, I propose that there may be others based on the following:
- Some more knowledgable people here have proposed or countered vapour lock, fuel contamination and automatic fuel cut-off theories to various degrees - even if these are not enough on their own, loss of electrical during rotation at high temperature could combine with these in a way we have not yet considered
- Thrust is nonlinear, and while I'm not qualified to say how much loss of fuel flow or loss of thrust would be critical in this scenario we do know that it was a hot takeoff with significant weight and gear remaining down - I know others here have run sims but I don't think anyone has focused on specific thrust / fuel flow params
- While electric fuel pumps might not be physically necessary for takeoff, my final point is: why are they required for takeoff? Is it not to mitigate cavitation, fuel sloshing at rotation, or any other kind of problem that might be relevant here?
Cavitating destroys pumps rapidly - someone upthread said replacing the fuel pump immediately is SOP if it has suction fed. Expect end of life in tens of hours rather than tens of thousands.
Some aircraft have switched to using jet/venturi pumps powered by returned fuel, like the A220. The electric boost pumps there are mainly for redundancy and are shut down in cruise; only one in each wing tank. Some A320s replace the centre override pumps with venturi transfer pumps.
July 09, 2025, 07:04:00 GMT
permalink Post: 11918167
Air India jet's fuel switches in focus, as crash preliminary report nears
From
Reuters
Summary
Summary
- Air India crash probe focuses on engine fuel control switches - source
- Preliminary report expected by Friday - sources
- Report could provide early details into world's worst aviation disaster in a decade
- Probe has been dogged by questions over lack of information
- India reversed course and now allowing UN specialist observer status - sources
July 8 (Reuters) - A preliminary report into the deadly crash of an Air India jetliner in June is expected to be released by Friday, three sources with knowledge of the matter said, with one adding the probe had narrowed its focus to the movement of the plane's fuel control switches.
The London-bound Boeing (BA.N) 787 Dreamliner, which started losing height after reaching an altitude of 650 feet, crashed moments after takeoff from Ahmedabad, India, killing 241 of the 242 people on board and the rest on the ground.
The investigation into the Air India crash is focusing on the movement of the engine fuel control switches following an analysis of the 787's flight and voice data recorders, along with a simulation by Boeing of the aircraft's final moments, one of the sources said.
The investigation has not raised any immediate concerns over mechanical failure, the source said, and there has been no bulletin to airlines recommending changes to 787 operations . Boeing declined to comment.
Aviation industry publication the Air Current first reported the focus on the fuel switches that help power the plane's two engines.
It was not clear what specific actions involving the fuel switches are being looked at by investigators. Sources told the Air Current that the available information on the black boxes could not rule in or out improper, inadvertent or intentional actions that preceded or followed the apparent loss of thrust before the aircraft crashed.
U.S. aviation safety expert John Cox said a pilot would not be able to accidentally move the fuel switches that feed the engines. "You can't bump them and they move," he said.
Cox added that if a switch was shut off, the effect would be almost immediate, cutting off engine power.
Most air crashes are caused by multiple factors. The investigation is focusing at least partly on engine thrust , Reuters reported last month.
While the report from Indian investigators could be made public on Friday, the three sources cautioned to Reuters that plans could change and there was no clarity on how much information would be available in the document, which comes about 30 days after the June 12 tragedy.
The sources spoke on condition of anonymity because they were not authorised to speak to media.
India's Aircraft Accident Investigation Bureau, which is leading the probe under international rules , did not respond immediately to a request for comment outside normal business hours.
However, India reversed course on an earlier decision reported by Reuters to prevent a U.N. aviation investigator from joining the probe, two senior sources said.
A specialist from the U.N.'s International Civil Aviation Organization (ICAO) was granted observer status, following an unusual request by the agency to offer its support.
ICAO declined to comment, adding in a statement that any public discussion of "cooperative arrangements," would require authorisation by the state.
The crash is challenging the Tata Group's ambitious campaign to restore Air India's reputation and revamp its fleet, after taking the carrier over from the government in 2022.
India is banking on a boom in aviation to support wider development goals, with New Delhi saying it wants India to be a job-creating global aviation hub along the lines of Dubai, which currently handles much of the country's international traffic.
A panel of Indian lawmakers will review safety in the country's civil aviation sector and has invited several industry and government officials to answer questions on Wednesday, with topics set to include the recent plane crash.
Reporting by Allison Lampert in Montreal and David Shepardson in Washington; Additional reporting by Dan Catchpole in Seattle and Kanjyik Ghosh in Bengaluru; Editing by Jamie Freed
The London-bound Boeing (BA.N) 787 Dreamliner, which started losing height after reaching an altitude of 650 feet, crashed moments after takeoff from Ahmedabad, India, killing 241 of the 242 people on board and the rest on the ground.
The investigation into the Air India crash is focusing on the movement of the engine fuel control switches following an analysis of the 787's flight and voice data recorders, along with a simulation by Boeing of the aircraft's final moments, one of the sources said.
The investigation has not raised any immediate concerns over mechanical failure, the source said, and there has been no bulletin to airlines recommending changes to 787 operations . Boeing declined to comment.
Aviation industry publication the Air Current first reported the focus on the fuel switches that help power the plane's two engines.
It was not clear what specific actions involving the fuel switches are being looked at by investigators. Sources told the Air Current that the available information on the black boxes could not rule in or out improper, inadvertent or intentional actions that preceded or followed the apparent loss of thrust before the aircraft crashed.
U.S. aviation safety expert John Cox said a pilot would not be able to accidentally move the fuel switches that feed the engines. "You can't bump them and they move," he said.
Cox added that if a switch was shut off, the effect would be almost immediate, cutting off engine power.
Most air crashes are caused by multiple factors. The investigation is focusing at least partly on engine thrust , Reuters reported last month.
While the report from Indian investigators could be made public on Friday, the three sources cautioned to Reuters that plans could change and there was no clarity on how much information would be available in the document, which comes about 30 days after the June 12 tragedy.
The sources spoke on condition of anonymity because they were not authorised to speak to media.
India's Aircraft Accident Investigation Bureau, which is leading the probe under international rules , did not respond immediately to a request for comment outside normal business hours.
INFORMATION RELEASE
The probe has been dogged by questions over lack of information, after investigators took about two weeks to download flight recorder data after the crash. The Indian government held only one press conference on the incident, and no questions were taken.However, India reversed course on an earlier decision reported by Reuters to prevent a U.N. aviation investigator from joining the probe, two senior sources said.
A specialist from the U.N.'s International Civil Aviation Organization (ICAO) was granted observer status, following an unusual request by the agency to offer its support.
ICAO declined to comment, adding in a statement that any public discussion of "cooperative arrangements," would require authorisation by the state.
The crash is challenging the Tata Group's ambitious campaign to restore Air India's reputation and revamp its fleet, after taking the carrier over from the government in 2022.
India is banking on a boom in aviation to support wider development goals, with New Delhi saying it wants India to be a job-creating global aviation hub along the lines of Dubai, which currently handles much of the country's international traffic.
A panel of Indian lawmakers will review safety in the country's civil aviation sector and has invited several industry and government officials to answer questions on Wednesday, with topics set to include the recent plane crash.
Reporting by Allison Lampert in Montreal and David Shepardson in Washington; Additional reporting by Dan Catchpole in Seattle and Kanjyik Ghosh in Bengaluru; Editing by Jamie Freed
July 09, 2025, 11:00:00 GMT
permalink Post: 11918308
For what it's worth, if the fuel control switches were rapidly cycled as per the dual engine failure memory actions, the engines should both have restarted and recovered full thrust within a matter of seconds. This is part of the certification and Rolls Royce publish the procedure (unofficially) as a last-ditch attempt to recover an engine that's experiencing a locked-in surge condition.
July 09, 2025, 11:07:00 GMT
permalink Post: 11918314
For what it's worth, if the fuel control switches were rapidly cycled as per the dual engine failure memory actions, the engines should both have restarted and recovered full thrust within a matter of seconds. This is part of the certification and Rolls Royce publish the procedure (unofficially) as a last-ditch attempt to recover an engine that's experiencing a locked-in surge condition.
Last edited by OliTom; 9th July 2025 at 11:24 .
July 09, 2025, 12:32:00 GMT
permalink Post: 11918361
For what it's worth, if the fuel control switches were rapidly cycled as per the dual engine failure memory actions, the engines should both have restarted and recovered full thrust within a matter of seconds. This is part of the certification and Rolls Royce publish the procedure (unofficially) as a last-ditch attempt to recover an engine that's experiencing a locked-in surge condition.
July 09, 2025, 12:35:00 GMT
permalink Post: 11918363
Another question if I may? I've tried searching but find the search function quite perplexing! Anyway, didn't find this answered.
From other posts here, it's clear that the Cutoff switches have a mechanical locking system which requires the switch handles to be pulled outwards to disengage the lock, before they can be moved to Cutoff.
Question is, to a pilot who knows these switches, can both these switches be easily operated in this fashion in unison, i.e. I guess, with one hand, so that they are both unlocked and moved to off together? I imagine that would be quite difficult to do (unless that's what everyone routinely practices), so the result would not be simultaneous.
July 09, 2025, 12:45:00 GMT
permalink Post: 11918371
Firstly, it's not rapid cycling of the fuel control switches, you turn them off then back on and see if it starts, this can take more than a minute as you have to wait to see if the action was successful. Second problem as mentioned above, the speed was far too low for a successful relight, you would most likely end up with a hot start or no start, most likely with a lot of smoke out the back due to unburnt fuel.
edited to add, after reading about the 787 it seems it uses electrical power to start. Same sort of issue though if not enough power, which is likely given the RAT was out.
edited to add, after reading about the 787 it seems it uses electrical power to start. Same sort of issue though if not enough power, which is likely given the RAT was out.
Last edited by SloppyJoe; 9th July 2025 at 12:57 .
July 09, 2025, 13:09:00 GMT
permalink Post: 11918385
The idea is to set the switch to CUTOFF and then to ON as that resets the FADEC (the circuit that controls the engine) and hopefully clears any issues it might have. The hope is that the turbine is still rotating fast enough for the FADEC to restart it. I believe this works the same as the auto-relight feature.
The turbine rotation would also provide the electrical power for that.
Do a thread search on "detent" to learn more about the construction of these switches than you ever wanted to know.
There's also a section on them in paulross 's https://paulross.github.io/pprune-th...171/index.html , but it may not be up to date. (Still a great resource, though.)
Unfortunately the wikipost linking to it is gone, presumably a victim to the recent forum changes.
The turbine rotation would also provide the electrical power for that.
Do a thread search on "detent" to learn more about the construction of these switches than you ever wanted to know.
There's also a section on them in paulross 's https://paulross.github.io/pprune-th...171/index.html , but it may not be up to date. (Still a great resource, though.)
Unfortunately the wikipost linking to it is gone, presumably a victim to the recent forum changes.
July 09, 2025, 14:45:00 GMT
permalink Post: 11918435
As a 787 operator I can observe a couple of things......
Deliberately cycling the Engine Cutoff switches just after rotate, in response to a dual power loss is inconceivable. You are way too low and slow for it to have any effect and your attention is better devoted to aiming for the flattest area ahead to crash into. Commencing the Dual Eng Fail/Stall checklist memory items is conditional upon both engines being at sub-idle and the aircraft being within the in-flight relight envelope. Neither of those conditions existed.
The flight recorder will witness what came first - Power loss or Start Switches to Cutoff? It seems the 'Third Contingency' that I alluded to about a thousand posts ago, sadly now seems likely. Given the iron-grip that the government appears to have over the media, one wonders how the truth will ever surface?
Deliberately cycling the Engine Cutoff switches just after rotate, in response to a dual power loss is inconceivable. You are way too low and slow for it to have any effect and your attention is better devoted to aiming for the flattest area ahead to crash into. Commencing the Dual Eng Fail/Stall checklist memory items is conditional upon both engines being at sub-idle and the aircraft being within the in-flight relight envelope. Neither of those conditions existed.
The flight recorder will witness what came first - Power loss or Start Switches to Cutoff? It seems the 'Third Contingency' that I alluded to about a thousand posts ago, sadly now seems likely. Given the iron-grip that the government appears to have over the media, one wonders how the truth will ever surface?
July 09, 2025, 16:26:00 GMT
permalink Post: 11918497
There has been discussion recently about a procedure that involves moving the fuel switches to CUTOFF and then back to RUN following a dual engine failure.
Attached is an image of a page from the Air India 787 Training Manual that discusses this procedure.
I am submitting this without comment or opinion.
Attached is an image of a page from the Air India 787 Training Manual that discusses this procedure.
I am submitting this without comment or opinion.
July 09, 2025, 16:34:00 GMT
permalink Post: 11918504
For info only - re-post of lever-lock fuel-switch design:
B787 Fuel Control Switches -
B787 Fuel Control Switches -
Last edited by PJ2; 9th July 2025 at 16:45 . Reason: Add image of B787 Fuel Control Switches
July 09, 2025, 16:38:00 GMT
permalink Post: 11918511
Theory alert : If you don\x92t have, or delete the cruise altitude in the FMC the aircraft will command a level off at 400ft, with the thrust levers reducing thrust significantly (I\x92ve seen it in the sim and happened at least once for real to my operator). It\x92s easy to do when loading the descent winds if you hit the wrong button. Could this have been confused with a loss of thrust?
And I would say the cut off switches do make a fairly unique click when being moved - I can hear it in my head as I write this!
And I would say the cut off switches do make a fairly unique click when being moved - I can hear it in my head as I write this!
July 09, 2025, 17:14:00 GMT
permalink Post: 11918533
Yeah but thought it worth discussing again IF we believe that the engine failure was caused by a pilot selecting both fuel control switches to cutoff. You\x92re right that I can\x92t imagine myself doing it but fear can make our inner chimps do strange things in response to the flight or flight response. (See the chimp paradox book).
In what world would you feather both props instead of selecting landing flaps in Nepal and cause a fatal crash? Seemed pretty inconceivable until it happened. What we all would do in the comfort of our armchairs is very different to what can happen in the heat of the moment.
In what world would you feather both props instead of selecting landing flaps in Nepal and cause a fatal crash? Seemed pretty inconceivable until it happened. What we all would do in the comfort of our armchairs is very different to what can happen in the heat of the moment.
Last edited by Propellerhead; 9th July 2025 at 17:37 .
July 09, 2025, 17:20:00 GMT
permalink Post: 11918536
Yeah but thought it worth discussing again IF we believe that the engine failure was caused by a pilot selecting both fuel control switches to cutoff. You\x92re right that I can\x92t imagine myself doing it but fear can make our inner chimps do strange things in response to the flight or flight response. (See the chimp paradox book).
July 09, 2025, 17:22:00 GMT
permalink Post: 11918540
Not a Boeing but the aircraft I last flew, if you turned off the fuel nothing would happen unless the power levers were below a certain power setting. You had to reduce the power levers, maybe to idle, can\x92t remember, then the fuel switches off.
July 09, 2025, 17:27:00 GMT
permalink Post: 11918542