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Musician
January 27, 2026, 06:43:00 GMT
permalink Post: 12027802

Quote:

Originally Posted by nikplane

I know: On the B787, the two EAFRs (front and rear), only the front EAFR, is self-powered by the RIPS (Recorder Independent Power Supply) for 10 minutes in the event of a power failure.

Therefore,cockpit voices and sounds are recorded by the front EAFR
even in the event all 28VDC power failure.

Yes. We have 36 posts on the RIPS, see the thread index https://paulross.github.io/pprune-th...171/index.html built by the esteemed paulross .

Subjects EAFR RIPS

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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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Musician
February 02, 2026, 09:50:00 GMT
permalink Post: 12030995

Quote:

Originally Posted by CV880

I came across one of Jeremy John Thompson's videos a couple of days ago and a quick glance at his channel reveals about 17 videos on AI171 and 787 systems. Talk about being obsessed!

The 18th video is him getting angry at AVHerald commenters calling him out. He says, "[1:11] You don't have access to the data. When we get the data, you'll see that I'm correct because it's impossible to be incorrect."

Subjects AI171 AvHerald

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Musician
February 02, 2026, 15:07:00 GMT
permalink Post: 12031133

Quote:

Originally Posted by JustusW

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.

3) Why this only happens at Air India.

Subjects: None

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

Quote:

Originally Posted by Ver5pen

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

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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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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Musician
February 03, 2026, 11:03:00 GMT
permalink Post: 12031515

We'll see what the physical evidence says.
If the log entry is correct, VT-ANX has a thrust control module with a demonstrably defective switch, which AI needs to pull, and the AAIB can examine.
They also have the burnt TCM of VT-ANB, and that has been to the lab as well, and the AAIB should know exactly by now whether these switches were latching or not.

Subjects AAIB (All)

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Musician
February 03, 2026, 14:02:00 GMT
permalink Post: 12031615

The document from the tweet, in full:

https://www.pib.gov.in/PressReleaseP...6&reg=3&lang=1

Ministry of Civil Aviation

Rejoinder on News Item relating to purported malfunction of Fuel Cut Off Switch on M/s Air India Boeing B787-8 aircraft VT-ANX

Posted On: 03 FEB 2026 5:27PM by PIB Delhi
.

On 01.02.2026, Air India B787-8 aircraft VT-ANX operated flight AI 132 (London- Bangalore). During engine start in London, on two occasions crew observed that the fuel control switch did not remain positively latched in the “RUN” position when light vertical pressure was applied. On the third attempt, the switch latched correctly in “RUN” and subsequently remained stable. Before continuing with the rest of procedure, a physical verification was performed by the crew to confirm that the switch was fully and positively latched in the “RUN” position. No abnormal engine parameters, cautions, warnings, or related system messages were observed during engine start or at any time thereafter. The operating crew member was briefed on the observation, unnecessary contact with the switch was avoided, and engine indications and alerting systems were closely monitored by the crew for the remainder of the flight. The flight was completed without incident.

After landing at Bangalore, crew reported the defect in the PDR. Air India referred the matter to M/s Boeing for further guidance. Based on the M/s Boeing recommended checks to establish the serviceability of fuel control switch, M/s Air India engineering observed that:

“Both left and right switches were checked and found satisfactory, with the locking tooth/pawl fully seated and not slipping from RUN to CUTOFF. When full force was applied parallel to the base plate, the switch remained secure. However, applying external force in an incorrect direction caused the switch to move easily from RUN to CUTOFF, due to the angular base plate allowing slip when pressed improperly with finger or thumb.”

In addition, based on Boeing’s communication, the pull-to-unlock force was checked on the fuel control switch using the recommended procedure on the involved fuel cut off switch, the fuel control unit to be installed and fuel cut off switch of another aircraft. In all cases the pull-to-unlock force was found within limits. These inspections were carried out in the presence of DGCA officers.

The video currently circulating on social media was analysed in light of Boeing recommended procedures, and it was observed that the procedure demonstrated in the video being circulated is incorrect.

The airline is being advised to circulate the Boeing recommended procedure for the operation of Fuel CUT OFF switch to its crew members.

Subjects DGCA Fuel (All) Fuel Cutoff Fuel Cutoff Switches Parameters RUN/CUTOFF

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Musician
February 03, 2026, 14:45:00 GMT
permalink Post: 12031656

Quote:

Originally Posted by Pilot DAR

Both of these topics relate to the switch(es) in the 787, but I think that the similarity ends there.

We already have several threads on AI171 issues (at least one of them in Tech Log ), so moving this discussion to its own thread seems unproblematic.

The significance of this new finding is that it makes accidental movement more likely. We already know about the incident where a sun visor fell and moved the switch. We are learning now that the mechanism of "pull up, then move the switch" can be circumvented, and that the switch can be moved by a single application of force. It appears that the engineers were able to reproduce this behaviour, so it's no longer just that crew's word.

So while on VT-ANB both switches moved at the same time, and that is unlikely to happen by itself, it now appears possible that an external force such as a loose object or an inadvertant pilot motion could have moved both switches. At least, this requires further study to narrow down the conditions for it, and to check whether these conditions were present on the accident flight.

Subjects AI171

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Musician
February 03, 2026, 18:53:00 GMT
permalink Post: 12031774

Quote:

Originally Posted by Pilot DAR

I read a report of a problem. I'm not sure that I actually see a report that there truly was a problem.

Preceding a "however" This was reported:

If a "however" is written after that statement, it is either meaningless and to be ignored, or it has the effect of negating the statement. There is no "partly airworthy" for these switches. It can't be both statements. Thus, my doubt about the credibility/applicability of this whole situation in the context of the 171 crash, subject to these two statements being reconciled with each other.

I really, really want to see a better report on this.

I imagine one way for this to be true would be if the lever has some wiggle room, such that the teeth on it can move sideways past the teeth on the base, and then stick in that position where the lever is up and the flanks of the teeth are still touching. In that position, you could flip the switch back off without overcoming the detent. But if you operate the switch properly, with no sideways force, and seat the lever correctly in the ON position, then it'd be secure. That fits with the part of the press release about telling the pilots how to operate these switches properly.

Obviously I have no idea if this is true. I just want to give an example of how that switch might be operated one way to be unsafe, and another way to be safe. I'd really want to see Boeing's take on this, and not a third-hand press release that went from Boeing to Air India engineering to ??? to the ministry. It may say something impossible that differs from the possible thing the engineers actually found.

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

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Musician
February 04, 2026, 11:16:00 GMT
permalink Post: 12032148

Quote:

Originally Posted by Chernobyl

The problem with your stated concern is how do you prevent it? Simple, you say: interlock it with the thrust levers and/or radio alt and/or baro alt in some combination to ensure you can ONLY switch to cutoff if not below 400' ft or at takeoff thrust. But what happens if this new logic fails in a novel way in the future preventing an engine shutdown when it really IS needed? Any new complexity adds potential unintended consequences and hence risks. Is the cure worse than the disease? Right now, the switch design is entirely consistent with Boeing standard practice: flight crew actions are the final say.

AFAIK Embraer has the switches interlocked with the thrust levers so they won't cut off unless at idle, and Citations require moving the thrust lever past idle?
Obviously Boeing can't easily change "standard practice", especially if they want to keep training costs for pilots switching types low, but that doesn't mean it's not a good idea in general.
If this logic fails "when it is really needed", the pilot can still pull the fire handle. Or the engine won't start, but then they'd still be sitting at the airport. But I don't think the aircraft that already have this have had issues?

Subjects Engine Failure (All) Engine Shutdown Fuel (All) Fuel Cutoff Switches

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Musician January 27, 2026, 06:43:00 GMT permalink Post: 12027802	Quote: Originally Posted by nikplane I know: On the B787, the two EAFRs (front and rear), only the front EAFR, is self-powered by the RIPS (Recorder Independent Power Supply) for 10 minutes in the event of a power failure. Therefore,cockpit voices and sounds are recorded by the front EAFR even in the event all 28VDC power failure. Yes. We have 36 posts on the RIPS, see the thread index https://paulross.github.io/pprune-th...171/index.html built by the esteemed paulross . Subjects EAFR RIPS Links are to this post in the relevant subject page so that this post can be seen in context. 2 recorded likes for this post. Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
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) Links are to this post in the relevant subject page so that this post can be seen in context. 2 recorded likes for this post. Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
Musician February 02, 2026, 09:50:00 GMT permalink Post: 12030995	Quote: Originally Posted by CV880 I came across one of Jeremy John Thompson's videos a couple of days ago and a quick glance at his channel reveals about 17 videos on AI171 and 787 systems. Talk about being obsessed! The 18th video is him getting angry at AVHerald commenters calling him out. He says, "[1:11] You don't have access to the data. When we get the data, you'll see that I'm correct because it's impossible to be incorrect." Subjects AI171 AvHerald Links are to this post in the relevant subject page so that this post can be seen in context. 2 recorded likes for this post. Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
Musician February 02, 2026, 15:07:00 GMT permalink Post: 12031133	Quote: Originally Posted by JustusW 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. 3) Why this only happens at Air India. Subjects: None 4 recorded likes for this post. Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
Musician February 02, 2026, 15:26:00 GMT permalink Post: 12031139	Quote: Originally Posted by Ver5pen 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 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) Links are to this post in the relevant subject page so that this post can be seen in context. 5 recorded likes for this post. Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
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 Links are to this post in the relevant subject page so that this post can be seen in context. 5 recorded likes for this post. Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
Musician February 03, 2026, 11:03:00 GMT permalink Post: 12031515	We'll see what the physical evidence says. If the log entry is correct, VT-ANX has a thrust control module with a demonstrably defective switch, which AI needs to pull, and the AAIB can examine. They also have the burnt TCM of VT-ANB, and that has been to the lab as well, and the AAIB should know exactly by now whether these switches were latching or not. Subjects AAIB (All) Links are to this post in the relevant subject page so that this post can be seen in context. 2 recorded likes for this post. Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
Musician February 03, 2026, 14:02:00 GMT permalink Post: 12031615	The document from the tweet, in full: https://www.pib.gov.in/PressReleaseP...6&reg=3&lang=1 Ministry of Civil Aviation *Rejoinder on News Item relating to purported malfunction of Fuel Cut Off Switch on M/s Air India Boeing B787-8 aircraft VT-ANX* Posted On: 03 FEB 2026 5:27PM by PIB Delhi . On 01.02.2026, Air India B787-8 aircraft VT-ANX operated flight AI 132 (London- Bangalore). During engine start in London, on two occasions crew observed that the fuel control switch did not remain positively latched in the “RUN” position when light vertical pressure was applied. On the third attempt, the switch latched correctly in “RUN” and subsequently remained stable. Before continuing with the rest of procedure, a physical verification was performed by the crew to confirm that the switch was fully and positively latched in the “RUN” position. No abnormal engine parameters, cautions, warnings, or related system messages were observed during engine start or at any time thereafter. The operating crew member was briefed on the observation, unnecessary contact with the switch was avoided, and engine indications and alerting systems were closely monitored by the crew for the remainder of the flight. The flight was completed without incident. After landing at Bangalore, crew reported the defect in the PDR. Air India referred the matter to M/s Boeing for further guidance. Based on the M/s Boeing recommended checks to establish the serviceability of fuel control switch, M/s Air India engineering observed that: “Both left and right switches were checked and found satisfactory, with the locking tooth/pawl fully seated and not slipping from RUN to CUTOFF. When full force was applied parallel to the base plate, the switch remained secure. However, applying external force in an incorrect direction caused the switch to move easily from RUN to CUTOFF, due to the angular base plate allowing slip when pressed improperly with finger or thumb.” In addition, based on Boeing’s communication, the pull-to-unlock force was checked on the fuel control switch using the recommended procedure on the involved fuel cut off switch, the fuel control unit to be installed and fuel cut off switch of another aircraft. In all cases the pull-to-unlock force was found within limits. These inspections were carried out in the presence of DGCA officers. The video currently circulating on social media was analysed in light of Boeing recommended procedures, and it was observed that the procedure demonstrated in the video being circulated is incorrect. The airline is being advised to circulate the Boeing recommended procedure for the operation of Fuel CUT OFF switch to its crew members. Subjects DGCA Fuel (All) Fuel Cutoff Fuel Cutoff Switches Parameters RUN/CUTOFF Links are to this post in the relevant subject page so that this post can be seen in context. No recorded likes for this post (could be before pprune supported 'likes'). Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
Musician February 03, 2026, 14:45:00 GMT permalink Post: 12031656	Quote: Originally Posted by Pilot DAR Both of these topics relate to the switch(es) in the 787, but I think that the similarity ends there. We already have several threads on AI171 issues (at least one of them in Tech Log ), so moving this discussion to its own thread seems unproblematic. The significance of this new finding is that it makes accidental movement more likely. We already know about the incident where a sun visor fell and moved the switch. We are learning now that the mechanism of "pull up, then move the switch" can be circumvented, and that the switch can be moved by a single application of force. It appears that the engineers were able to reproduce this behaviour, so it's no longer just that crew's word. So while on VT-ANB both switches moved at the same time, and that is unlikely to happen by itself, it now appears possible that an external force such as a loose object or an inadvertant pilot motion could have moved both switches. At least, this requires further study to narrow down the conditions for it, and to check whether these conditions were present on the accident flight. Subjects AI171 Links are to this post in the relevant subject page so that this post can be seen in context. 3 recorded likes for this post. Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
Musician February 03, 2026, 18:53:00 GMT permalink Post: 12031774	Quote: Originally Posted by Pilot DAR I read a report of a problem. I'm not sure that I actually see a report that there truly was a problem. Preceding a "however" This was reported: If a "however" is written after that statement, it is either meaningless and to be ignored, or it has the effect of negating the statement. There is no "partly airworthy" for these switches. It can't be both statements. Thus, my doubt about the credibility/applicability of this whole situation in the context of the 171 crash, subject to these two statements being reconciled with each other. I really, really want to see a better report on this. I imagine one way for this to be true would be if the lever has some wiggle room, such that the teeth on it can move sideways past the teeth on the base, and then stick in that position where the lever is up and the flanks of the teeth are still touching. In that position, you could flip the switch back off without overcoming the detent. But if you operate the switch properly, with no sideways force, and seat the lever correctly in the ON position, then it'd be secure. That fits with the part of the press release about telling the pilots how to operate these switches properly. Obviously I have no idea if this is true. I just want to give an example of how that switch might be operated one way to be unsafe, and another way to be safe. I'd really want to see Boeing's take on this, and not a third-hand press release that went from Boeing to Air India engineering to ??? to the ministry. It may say something impossible that differs from the possible thing the engineers actually found. Subjects Fuel (All) Fuel Cutoff Switches Fuel Cutoff Switches (detent) Links are to this post in the relevant subject page so that this post can be seen in context. 1 recorded likes for this post. Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
Musician February 04, 2026, 11:16:00 GMT permalink Post: 12032148	Quote: Originally Posted by Chernobyl The problem with your stated concern is how do you prevent it? Simple, you say: interlock it with the thrust levers and/or radio alt and/or baro alt in some combination to ensure you can ONLY switch to cutoff if not below 400' ft or at takeoff thrust. But what happens if this new logic fails in a novel way in the future preventing an engine shutdown when it really IS needed? Any new complexity adds potential unintended consequences and hence risks. Is the cure worse than the disease? Right now, the switch design is entirely consistent with Boeing standard practice: flight crew actions are the final say. AFAIK Embraer has the switches interlocked with the thrust levers so they won't cut off unless at idle, and Citations require moving the thrust lever past idle? Obviously Boeing can't easily change "standard practice", especially if they want to keep training costs for pilots switching types low, but that doesn't mean it's not a good idea in general. If this logic fails "when it is really needed", the pilot can still pull the fire handle. Or the engine won't start, but then they'd still be sitting at the airport. But I don't think the aircraft that already have this have had issues? Subjects Engine Failure (All) Engine Shutdown Fuel (All) Fuel Cutoff Switches Links are to this post in the relevant subject page so that this post can be seen in context. 1 recorded likes for this post. Reply to this quoting this original post. You need to be logged in. Not available on closed threads.

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