Fuel (All) Page: 54 of 56

Musician
February 01, 2026, 22:18:00 GMT
permalink Post: 12030849

Quote:

Originally Posted by nikplane

Hello everyone.
There's this rumor and/or question going around:
Someone was promoting the idea that a diode failure in the backup battery had disabled the battery and both buses.
He claimed that the FDR inputs from the switch sensors were coming from opto-isolators, and since they had lost power, they showed the switches going into the open state until power returned from the RAT.
For this theory to be valid, a single diode failure would have had to disable the entire aircraft.

Please,
- just comments on technical aspects?
- It's unclear this refers to the forward EAFR backup battery or
the Hot Battery Bus (Hot BB).

Thanks

The engines have their own power supply, separate connections to the cutoff switches and thrust lever angle resolvers, and would be unaffected in this scenario.

Notwithstanding the fact that this failure mode is also technically implausible/impossible. Here's a 787 that landed with the battery on fire:
https://skybrary.aero/accidents-and-...and-japan-2013

On 16 January 2013, a Boeing 787-8 (JA804A) being operated by All Nippon Airways (ANA) on a scheduled passenger flight from Yamaguchi-Ube to Tokyo Haneda in day Visual Meteorological Conditions (VMC) made an emergency diversion to Takamatsu after a main battery failure was annunciated climbing through FL320.

.
The original perpetrator of this idea is Jeremy John Thompson, with a Youtube video titled "How Air India AI171 B787 crashed - Lithium Battery Diode Module Failure" positing that the battery diode module failed, the battery overcharged and short-circuited, and disaster ensued. This was half a year ago.

Last edited by Musician; 1st February 2026 at 22:41 .

Subjects AI171 EAFR FDR Fuel (All) Fuel Cutoff Switches RAT (All)

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JustusW
February 02, 2026, 13:20:00 GMT
permalink Post: 12031080

Quote:

Originally Posted by Den2020

On Feb 2nd 2026 the crew of an Air India Boeing 787-9, registration VT-ANX performing flight AI-132 from London Heathrow,EN (UK) to Bangalore (India), observed during engine start, that the left hand fuel control switch failed to remain in the RUN position two times and moved towards the CUTOFF position.

So here's what we'll be discussing next:
1) How Air India faked this emergency.
2) How Boeing is covering up this massive safety flaw.

Although just by the description alone I can't even create a mental image of the failure mode given the actual construction of the switches. Not only are they latching into the detent, but what could possibly apply a downward force? Would gravity alone move a switch of this type even if the guard was completely removed? By their nature switches tend to be mechanically bistable, meaning they have two stable positions regardless of any switch guards.
Maybe someone with actual knowledge of the switches can chime in here. For me this sounds very strange and raises all sorts of red flags.

Subjects Fuel (All) Fuel Cutoff Switches Fuel Cutoff Switches (detent) RUN/CUTOFF Switch Guards

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Pilot DAR
February 02, 2026, 13:32:00 GMT
permalink Post: 12031086

Quote:

that the left hand fuel control switch failed to remain in the RUN position two times and moved towards the CUTOFF position.

Having operated this type of switch for about a half century, I am unconvinced that a properly selected switch could "move towards the cutoff position".

From post 166 of this thread:

Quote:

Consider this post with a picture of the switches in question:

They must be lifted over the detent (if installed correctly) in each direction.

Perhaps the switch could be defective, but that is (a) easily detectable by the pilot) and (b) still not likely to result in it moving on its own, rather just not locking well in the selected position. This is a situation where readers need to apply their understanding before accepting an unsubstantiated report. If we receive an authoritative report about how this switch "moved toward cutoff" twice on its own, I will read with great interest!

Subjects Fuel (All) Fuel Cutoff Switches Fuel Cutoff Switches (detent) RUN/CUTOFF

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Ver5pen
February 02, 2026, 14:19:00 GMT
permalink Post: 12031107

Quote:

Originally Posted by Pilot DAR

Having operated this type of switch for about a half century, I am unconvinced that a properly selected switch could "move towards the cutoff position".

From post 166 of this thread:

Perhaps the switch could be defective, but that is (a) easily detectable by the pilot) and (b) still not likely to result in it moving on its own, rather just not locking well in the selected position. This is a situation where readers need to apply their understanding before accepting an unsubstantiated report. If we receive an authoritative report about how this switch "moved toward cutoff" twice on its own, I will read with great interest!

the AVherald report notes this happened twice and was observed by type rated 787 crew

are we saying that crew don\x92t know how to operate these switches? The first time one could argue they didn\x92t seat it properly but the second time? I would assume all 787 (particularly air india) are VERY sensitive and deliberate with this particularly switch post 171

the plane is now grounded by the airline so something happened

Subjects AvHerald Fuel (All) Fuel Cutoff Switches

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TURIN
February 02, 2026, 15:04:00 GMT
permalink Post: 12031129

Quote:

Originally Posted by TURIN

Did the aircaft operate that particular sector after the crew reported the 'fault' or did they continue?

I'll answer my own question.
According to FR24.
The aircraft took off 35 minutes late.

So we are being led to believe that a potentially critical system failure was observed during engine start, subsequently ignored, the aircraft operated it's scheduled service back to India.
Alternatively, the #1 fuel cut off switch was replaced, system checks, including an engine start, performed and certified, all in 35 minutes or less?

I smell a rat.

Subjects FlightRadar24 Fuel (All) Fuel Cutoff Fuel Cutoff Switches

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Ver5pen
February 02, 2026, 15:16:00 GMT
permalink Post: 12031137

Quote:

Originally Posted by TURIN

sounds like they noted twice that the cutoff hadn\x92t seated properly and eventually got it gated (done in conjunction with maintenance who knows?)

and they continued on with no other dramas to their home base where the plane is now in the hands of maintenance

clearly *something* happened as I don\x92t think airlines are on the habit of grounding their $300m airliners for no reason.

i remember when the consensus was this issue (fuel cutoffs not seating properly) was nearly impossible yet this crew found differently.

maybe we should discuss new information on the merits of that and not frame everything as x party trying to shift blame

this is certainly noteworthy even if it ultimately has nothing to do with 171

Subjects FlightRadar24 Fuel (All) Fuel Cutoff Fuel Cutoff Switches

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Musician
February 02, 2026, 15:26:00 GMT
permalink Post: 12031139

Quote:

Originally Posted by Ver5pen

We can even explain it with old information, because we have the advisory that, on these switches, the base can twist versus the lever cap such that the detents no longer match. Then switch travel is reduced such that the internal spring in the switch itself no longer locks positively, and then vibrations and gravity could make it move?
A mechanic/engineer looking at the switch could twist it back so that it locks ok, with very little effort.
If so, Air India should replace these switches with the safer switch model ASAP.

Subjects Fuel (All) Fuel Cutoff Switches Fuel Cutoff Switches (detent)

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JustusW
February 02, 2026, 15:33:00 GMT
permalink Post: 12031144

Quote:

Originally Posted by Ver5pen

clearly *something* happened as I don\x92t think airlines are on the habit of grounding their $300m airliners for no reason.

i remember when the consensus was this issue (fuel cutoffs not seating properly) was nearly impossible yet this crew found differently.

There is way too little known and way too many possibilities for why the airline would ground an aircraft with any kind of issue on that particular switch. It should be noted, that the source for this "incident" is itself highly questionable. Just one of the many "aviation safety experts" with a notable lack of any actual safety work in their CVs but an impressive list of press releases...

Also the consensus was that it was nearly impossible for the fuel cutoffs to leave the seated position. Obstruction of the detents is and always will be a distinct possibility. In this case it would have actually worked as intended, as it forced the crew to remove or fix the detent issue before being able to operate the flight normally.

In fact an obstruction or damage to the switch guard detent is pretty much the only way I can imagine this working if, for example, the detent ring itself was twisted or otherwise misaligned relative to the switch motion of travel it might have been kept from actually latching into the switches own stable position explaining why it moved into the other stable position. Which again would be a safe state as it would occur before engine startup was even attempted.
I doubt we will ever get an update on this one though.

Subjects Fuel (All) Fuel Cutoff Switches Fuel Cutoff Switches (detent) Switch Guards

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JustusW
February 02, 2026, 15:37:00 GMT
permalink Post: 12031147

Quote:

Originally Posted by Ver5pen

sounds like they discovered the issue on engine start, reported the issue and carried on the flight to their home base where the aircraft is AOG for maintenance related activities

I don't think either of the fuel cutoff switches are on the MEL. They're probably considered safety critical given the whole "fire and death" thing they're supposed to guard against.

Subjects Fuel (All) Fuel Cutoff Fuel Cutoff Switches MEL Switch Guards

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JustusW
February 02, 2026, 16:20:00 GMT
permalink Post: 12031171

Quote:

Originally Posted by Den2020

The foundation stated when asked why the aircraft departed nonetheless: "The issue is, there is no guidance." ... unbelievable

Christ almighty... When I was quipping about the MEL I didn't actually expect a pilot to take off with a faulty item very very very definitely not on it...

So much for the quality of this "Safety Matters Foundation". There is guidance. If it's broke and it's not exempt your aircraft is grounded. Considering this happened AFTER the incident discussed in this thread it almost makes me reconsider the accidental double switch movement theory... They might never have swapped the switches as per the original directive, and it might just have been common practice to mash dem buttons until they "stuck".
How do you fly an Air India plane post AI171 and do that if it's not widely employed common practice?

Quote:

Originally Posted by Andy_S

It should not be physically possible for the switch to behave in the way described. As someone said earlier, I smell a rat.....

I mean, now it almost makes more sense. Air India might just routinely be flying with deformed or misaligned detents on their fuel cutoff switches.
This is beginning to sound like the least insane explanation...

Subjects AI171 Fuel (All) Fuel Cutoff Fuel Cutoff Switches Fuel Cutoff Switches (detent) MEL

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Mb194dc
February 02, 2026, 16:24:00 GMT
permalink Post: 12031175

Very unusual events do occur sometimes. There can't be an easily repeatable problem with 787 cut off switches. Or wee see it often given 1175 of them are in service. That doesn't mean there isn't some ultra edge case problem though...

What odds a falling sun visor will shut an engine down, but that happened in December on 737 max 8.

Subjects Fuel (All) Fuel Cutoff Switches

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JustusW
February 02, 2026, 16:32:00 GMT
permalink Post: 12031183

Quote:

Originally Posted by Mb194dc

Well actually... There was a common problem with those switches. It was the topic of a rather old Airworthiness Directive and discussed extensively. Going off memory alone it was possible for the detents to be misaligned or otherwise damaged preventing the switches from correctly latching into either locked position.
As per the AD they _should_ have been replaced. It _should_ have been impossible for any switches with the issue to still be used on an aircraft over a decade after the AD. But maybe Air India just decided to not follow that AD? Or maybe there is a small subset of 787's where they didn't? And what the hell did they check last year when they supposedly went over all their 787's and inspected that very set of switches?!
I'm baffled and a bit speechless right now...

Subjects Air Worthiness Directives Fuel (All) Fuel Cutoff Switches Fuel Cutoff Switches (detent)

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Pilot DAR
February 02, 2026, 16:37:00 GMT
permalink Post: 12031185

Let's remember that totally independent of the external pull the toggle to unlock mechanism, internally, the switch still has the original over center mechanism which will spring the switch and contact to one extreme, or the other. Irrespective of the secondary locking feature, all quality toggle switches will spring to the intended position to prevent the switch contacts from resting just or just short of contact, and possibly arching internally.

Yes, if defective, the pull part of the toggle can rotate, and then the motion of the toggle will be abnormal. This would be entirely detectable in the moment by a pilot familiar with the operation of the switch. I see one of three situations here: The switch would operate properly, and the report is not accurate, the switch was operable, but the locking part of the toggle was not moving correctly (so the switch was defective), ans someone was satisfied that once positioned to run, it would remain there safely (suitably qualified mechanic, I hope, or the switch was entirely defective, so the flight could not depart until the switch was replaced. All three of these conditions are very easy for the pilots to understand. One does not require maintenance activity.

All of that said, I see this as peripheral at best to the Air India 171 crash. The preliminary report tells of both fuel cut off switches being found in the run position, and states that they were both moved from run to cutoff after takeoff within a second or so of each other, and then back to run. Nothing authoritative I have read so far from the Air India 171 crash suggests that either one of the fuel cutoff switches were defective. Indeed, the events of the accident suggest that when operated, they functioned exactly as intended! Their being found in the run position removes doubt that they (the locking feature) were operating properly. I think that the report of today, if credible, is unrelated to the 171 crash in causal information.

Subjects Fuel (All) Fuel Cutoff Fuel Cutoff Switches Preliminary Report

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JustusW
February 02, 2026, 16:56:00 GMT
permalink Post: 12031195

Quote:

Originally Posted by Pilot DAR

The preliminary report tells of both fuel cut off switches being found in the run position, and states that they were both moved from run to cutoff after takeoff within a second or so of each other, and then back to run. Nothing authoritative I have read so far from the Air India 171 crash suggests that either one of the fuel cutoff switches were defective. Indeed, the events of the accident suggest that when operated, they functioned exactly as intended! Their being found in the run position removes doubt that they (the locking feature) were operating properly. I think that the report of today, if credible, is unrelated to the 171 crash in causal information.

If the detent is misaligned/damaged enough the upper stable position may not be fully reachable and the switch might instead rest in a pseudo stable position prone to collapse due to vibration or other outside forces.

> The FAA issued Special Airworthiness Information Bulletin (SAIB) No. NM-18-33 on December 17, 2018, regarding the potential disengagement of the fuel control switch locking feature. [...] Both fuel control switch were found in the \x93RUN\x94 position.

So correction first: It wasn't an Airworthiness Directive, it was just an SAIB, but also the above is the only information provided by the preliminary report. Notably they did not comment in any way on the state of the guard/detent.
I'd not dismiss this event so out of hand. After the 171 crash every single pilot flying for Air India surely has heard that those switches are blamed, right? For any of them to be willing to faff around with those seems alarming and, for me at least, points to possible normalization of deviance. It may be practice for them to not treat these switches as a potential flight safety issue.

Subjects FAA Fuel (All) Fuel Cutoff Fuel Cutoff Switches Fuel Cutoff Switches (detent) Preliminary Report SAIB NM-18-33 Special Airworthiness Information Bulletin

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Musician
February 02, 2026, 18:15:00 GMT
permalink Post: 12031256

Quote:

Originally Posted by Farrell

https://www.ndtv.com/india-news/air-...Imagetopscroll

"Left fuel control switch slips from run to cut off when pushed down slightly. It does not lock in its position."

Subjects Fuel (All) Fuel Cutoff Switches

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buzzer90
February 02, 2026, 18:35:00 GMT
permalink Post: 12031263

Quote:

Originally Posted by Musician

"Left fuel control switch slips from run to cut off when pushed down slightly. It does not lock in its position."

1. A/C veering to the left, sounds like my car at the minute\x85

Subjects Fuel (All) Fuel Cutoff Switches

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Ver5pen
February 02, 2026, 18:44:00 GMT
permalink Post: 12031266

Quote:

Originally Posted by Musician

"Left fuel control switch slips from run to cut off when pushed down slightly. It does not lock in its position."

I\x92m sorry but dismissing this as not relevant in the 171 accident blows my mind

the same fleet operated by the same airline

I still think intentional action is the most obvious explanation but that will never be 100% concrete without definitive evidence (a note or previous suicidal ideation)

air India was hardly known to be a beacon of maintenance standards prior to their takeover by TATA and like a super carrier the ship takes a long time to turn around, their legacy fleet that they inherited was known to be particularly troubled. Google air india and spares and you\x92ll see they had a huge % of their fleet grounded for lack of support prior to TATA taking them over

\x91Until pressed down slightly\x92

Thisraises my eyebrow at least. So they appear functional until externally interfered with? I imagine 787 drivers and certainly AI crew today manipulate the fuel cutoffs when doing engine start ever since 171, I certainly do on the Bus ever since this incident to make sure it\x92s seated properly. hence it was picked up this time but was it before?

So a hand behind the TL or placing their hand back on or any other thing in that area that places pressure on those switches at the wrong moment. Wasn\x92t there an Atlas 767 that we speculate was lost because of an oversized watch (combined with sheer incompetence)?

again, I reiterate the most likely explanation is pilot suicide but can we rule out everything else? Extraordinary claims require extraordinary evidence and that goes both ways.

Subjects Fuel (All) Fuel Cutoff Switches

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TURIN
February 02, 2026, 18:53:00 GMT
permalink Post: 12031268

Quote:

Originally Posted by Musician

"Left fuel control switch slips from run to cut off when pushed down slightly. It does not lock in its position."

Wow! Just wow.
That is a log entry after arrival in Bangalore!

Subjects Fuel (All) Fuel Cutoff Switches

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DaveReidUK
February 02, 2026, 23:21:00 GMT
permalink Post: 12031352

Quote:

Originally Posted by TURIN

The aircraft pushed back at 21:19 - that's STD+14, not 35.

Subjects FlightRadar24 Fuel (All) Fuel Cutoff Fuel Cutoff Switches

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Lifer01
February 03, 2026, 00:36:00 GMT
permalink Post: 12031372

Quote:

Originally Posted by DaveReidUK

The aircraft pushed back at 21:19 - that's STD+14, not 35.

For reference, Boeing does not provide a procedure to replace the cut-off switches. If there is an issue with a fuel cut-off switch, the whole thrust control module is to be replaced, ie. the throttle levers and cut-off switches are in one module.

I believe this has been the case since before the AI accident.

Subjects Fuel (All) Fuel Cutoff Fuel Cutoff Switches

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