July 12, 2025, 22:28:00 GMT
permalink Post: 11920888
1 user liked this post.
Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
July 12, 2025, 22:46:00 GMT
permalink Post: 11920900
It seems to me that there must have been further dialogue after the bland "I didn't". To have nothing reported after that two-line exchange, until the MAYDAY at 08:09:05, is a highly suspect omission from the interim report. In a two-crew cockpit, facing a sudden dual engine rollback just after rotation, I find it very hard to believe that this two-line exchange was the only interaction captured.
Although published a little later than expected, it has now narrowed the speculator's focus from the wilder theories to the fuel switches.
Air India is not grounded, Boeing engines are not grounded and there are no recommended actions to engine operators and manufacturers.
Although a full verbatim transcript of the CVR could have been published, or even the recording itself, a decision has been made by the investigators not to do so. All we have is two bland paraphrases 'One of the pilots is heard asking the other why did he cutoff' (not even gramatically correct). 'The other pilot responded that he did not do so'.
Sometimes reports are more about what is not in them rather than was is in them.
It seems to me that the missing sections from the recording which would have revealed exact voice timings, language, tone, inflection and urgency which would have answered a lot of the questions on here have been deliberately withheld either temporarily or permanently. It is for the reader to infer why that might be. The investigators know much more but have chosen not to publicise it. I suspect they have more pieces of the jigsaw than we can see but probably not the full picture yet.
Last edited by T28B; 12th July 2025 at 23:06 . Reason: Formatting for ease of reading and pulling out key points
5 users liked this post.
Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
July 12, 2025, 22:55:00 GMT
permalink Post: 11920905
I have not seen this question asked anywhere and I'm a software engineer (non-aviation), so felt I had to ask it:
Do these solid-looking mechanical fuel switches really act directly upon the fuel system or are they routed via the control system as logic (0/1) signals?
It would certainly save a lot of copper and looming time to convert their output into a logic signal before it leaves the cockpit...
If the former, ignore all that follows, as it is wrong.
If the latter, a control software glitch or electrical noise/short could cause the fuel switches to appear to the control system as being briefly off,
while the pilots see the physical switches are still in the on position.
Even if such a noisy electrical signal rapidly reverted to correctly indicating fuel-switch on-state after even a few milliseconds,
any control system might well have embarked upon a relatively slow relight/startup/engine-protection procedure.
In such a scenario, the pilot who first noticed the engines spinning down would query it, while the other pilot would look at the physical switches and see that they were (still) on, and initially be non-plussed by the question.
Need to ask the question now satisfied.
Andy
Do these solid-looking mechanical fuel switches really act directly upon the fuel system or are they routed via the control system as logic (0/1) signals?
It would certainly save a lot of copper and looming time to convert their output into a logic signal before it leaves the cockpit...
If the former, ignore all that follows, as it is wrong.
If the latter, a control software glitch or electrical noise/short could cause the fuel switches to appear to the control system as being briefly off,
while the pilots see the physical switches are still in the on position.
Even if such a noisy electrical signal rapidly reverted to correctly indicating fuel-switch on-state after even a few milliseconds,
any control system might well have embarked upon a relatively slow relight/startup/engine-protection procedure.
In such a scenario, the pilot who first noticed the engines spinning down would query it, while the other pilot would look at the physical switches and see that they were (still) on, and initially be non-plussed by the question.
Need to ask the question now satisfied.
Andy
With that info, your scenario seems very unlikely.
Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
July 12, 2025, 22:59:00 GMT
permalink Post: 11920907
Fire extinguisher handles same function??
Just a thought \x97 the fire extinguisher handles perform the same function as the fuel cut-off.
Could there have been a strap /booklet or something else that accidentally got under the fire handles and activated them when one of the pilots pulled on the item?
The fire handles are not particularly well protected against something getting underneath them
Is there any information on whether the fuel cutoff switches and fire handles register as separate events on the flight data recorder, or if both are logged under a common indication, such as 'fuel switch cut off'?
Could there have been a strap /booklet or something else that accidentally got under the fire handles and activated them when one of the pilots pulled on the item?
The fire handles are not particularly well protected against something getting underneath them
Is there any information on whether the fuel cutoff switches and fire handles register as separate events on the flight data recorder, or if both are logged under a common indication, such as 'fuel switch cut off'?
Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
July 12, 2025, 23:05:00 GMT
permalink Post: 11920909
If it resulted in an eicas message, then the confused conversation, leading to (several) cycling attempts to reset them successfully to RUN, those 10 seconds later doesn\x92t sound unreasonable at all to me.
Not been in that situation, obviously, but I have certainly been in stressed situations where somewhere, someone (or something) pressed the wrong button, and I need to find out which one.
10 seconds is really not a long time if it is unexpected. It is very short.
Please also remember:
-We have no idea of exactly what was said. Whether the conversation referred to a error message, engines spooling down or physical switch movement/position. Throw in possible translation inaccuracies, and we can conclude even less from the information about the conversation, or what the level of clarity or confusion were.
-There is up to 2 seconds of margin of error in the time code of events because of the (speculated) sampling rate of 1Hz.
Not been in that situation, obviously, but I have certainly been in stressed situations where somewhere, someone (or something) pressed the wrong button, and I need to find out which one.
10 seconds is really not a long time if it is unexpected. It is very short.
Please also remember:
-We have no idea of exactly what was said. Whether the conversation referred to a error message, engines spooling down or physical switch movement/position. Throw in possible translation inaccuracies, and we can conclude even less from the information about the conversation, or what the level of clarity or confusion were.
-There is up to 2 seconds of margin of error in the time code of events because of the (speculated) sampling rate of 1Hz.
I'm talking about an electrical failure (for example a short), which is already implausibly affecting both (independent) circuits, causing an issue in a circuit that as I understand it fails open anyway, then resolving itself to become functional again - incidentally in roughly the same time frame that a pilot would notice an issue and seek to correct.
This doesn't require knowledge of the cockpit conversation or judgement on speed (or otherwise) of the recovery. It's purely that an already incredibly unlikely scenario (electrical failure) becomes even more unlikely with the spontaneous *and synchronised, but not perfectly so* removal of the fault state of whatever this failure was.
*Edit* Given my previous post has been removed it would appear that the mods also misread this to do with timing of *pilots response*, which I find a little odd as it was in response to a comment about electrical failure...
To be honest at this point for me we are immediately hamster wheeling again, and this time because any commentary around either electrical circuit issues (astronomical odds) or accidental device triggering cut off (no evidence nor can there be right now) are speculation in nature and have to be. Equally, while the obvious culprit is hands on the switches, any comments about why again are speculation and have to be.
There's nothing more anyone can get to on this one until further CVR data is released in my view. Bowing out.
Last edited by Mrshed; 12th July 2025 at 23:18 .
4 users liked this post.
Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
July 12, 2025, 23:06:00 GMT
permalink Post: 11920911
Tdracer has certainly explained that separation of cabling runs etc would have it very improbable that a single cable fault or short would impact both engines simultaneously in the same way. The CVR data is derived from local sensors with a dedicated battery backup, however all the FDR data and the fuel shut off commands are electrical signals which ultimately have a common source in the aircraft power buses. A water ingress into the EE bay at rotate which momentarily shorted all the low voltage buses to higher AC voltage is unlikely but is it unlikely to the same extent.
What bothers me is that message about the stab cutoff switches on the previous flight. It's a bit of a strange coincidence, since those switches are quite close to the fuel switches. I'm thinking that maybe some liquid could have been spilled during the previous flight over the area of the fuel switches and stab cutoff switches. Perhaps it initially affected just the stab switches. Then, during the accident flight, the acceleration and/or the rotation might have caused residual liquid to move and cause some issue for both fuel switches. Then, as the acceleration stopped after the loss of thrust and the aircraft stopped climbing, maybe the liquid moved again and the fuel switches recovered. But I admit this seems very unlikely.
3 users liked this post.
Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
July 12, 2025, 23:13:00 GMT
permalink Post: 11920915
Yes I totally agree, if it was deliberate there would have been a fight to prevent them being turned on again, until it was too late. As a previous post said, during a loss of thrust on both engines, your immediate comment is not \x93why did you cut off\x94 therefore it\x92s reasonable to assume he saw it happen, and then a 10 second fight to restore them ensued.
5 users liked this post.
Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
July 12, 2025, 23:30:00 GMT
permalink Post: 11920926
No simulator access, but I do know this much:
One EICAS and one PFD is on the battery (most likely the left seat PFD) - they might momentarily flicker but will not 'blank'.
You get an EICAS message when you set the fuel switch to CUTOFF - something like "ENGINE X CUTOFF" (not sure of the 787 wording, but it would be something to that effect.
While I doubt the PF would be actively monitoring EICAS during TO, with the sudden audio change to the engine noise as well as the sudden loss of acceleration, I'd expect him to take a quick look at EICAS to see what the (
) the engines are doing. Plus, if the PF was in the right seat and his PFD blanked - I'd expect him to look across to see what's on either the standby or the left seat PFC, and perhaps EICAS.
One EICAS and one PFD is on the battery (most likely the left seat PFD) - they might momentarily flicker but will not 'blank'.
You get an EICAS message when you set the fuel switch to CUTOFF - something like "ENGINE X CUTOFF" (not sure of the 787 wording, but it would be something to that effect.
While I doubt the PF would be actively monitoring EICAS during TO, with the sudden audio change to the engine noise as well as the sudden loss of acceleration, I'd expect him to take a quick look at EICAS to see what the (
) the engines are doing. Plus, if the PF was in the right seat and his PFD blanked - I'd expect him to look across to see what's on either the standby or the left seat PFC, and perhaps EICAS.
CVR should have recorded the beeper too, inhibits are for ground only.
6 users liked this post.
Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
July 12, 2025, 23:37:00 GMT
permalink Post: 11920930
Reminder: the prelim report didn't say exactly what the pilots said, and I also think it's unlikely that they said it in English anyway.
So there's no value in wondering what motivated one pilot to say "why did you cutoff" because we don't know if that's what was said.
The exact wording in the report is:
Given the need to couch the report's wording in neutral/diplomatic terms (expletives?), and almost certainly to translate the conversation from another language, the inferences being drawn from those lines in the report are going wildly beyond what is reasonable.
So there's no value in wondering what motivated one pilot to say "why did you cutoff" because we don't know if that's what was said.
The exact wording in the report is:
In the cockpit voice recording, one of the pilots is heard asking the other why did he cutoff.
The other pilot responded that he did not do so.
The other pilot responded that he did not do so.
12 users liked this post.
Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
July 12, 2025, 23:39:00 GMT
permalink Post: 11920931
3 users liked this post.
Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
July 12, 2025, 23:54:00 GMT
permalink Post: 11920939
My take is there is a lot of significant info purposely left out of the preliminary report. For instance, the status of the fuel cutoff switches was not mentioned. Maybe that is the info being sort by “stakeholders” and the “components of interest” that were “quarantined” were the fuel cutoff switches. “Initial leads” is also interesting.
1 user liked this post.
Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
July 13, 2025, 00:08:00 GMT
permalink Post: 11920951
Switch locking mechanism
I was just looking into these Honeywell TL family switches for a different project. There are certain part numbers that have the locking mechanism - the ones that don't are clearly different. I didn't see anything to indicate that the locking feature was selectable or defeatable. I suspect the faulty 737 switches fron 2018 had an issue with the detent machining or maybe the loading spring - i.e. a bad batch.
1 user liked this post.
Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
July 13, 2025, 00:15:00 GMT
permalink Post: 11920953
Throttle position and fuel control switch
The Indian AAIB are avoiding a German wings event I fear. Actually I was in a flight deck of a EJR today. Start / stop switches are so bloody obvious on the overhead as main switches. Guarded and easy to observe by all. Control switches that are not required as a normal action put away from hidden positions and visible to all. Embraer actually design systems logically. Speaking to a Captain today, he confirmed that if the the thrust levers of an EJR are beyond flight idle, engines cannot be shut down by then engine start/stop switches being turned off! You need to drag the thrust levers back to idle to shut them down. First thing I was taught as an airframe engineer converting to dual trade is that the fuel system of a airframe should not restrict an engine to receive fuel from a commanded input by the pilot. Throttle position should drive that logic. Not a lazy Boeing combined FADEC and SOV switch.
1 user liked this post.
Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
July 13, 2025, 00:16:00 GMT
permalink Post: 11920954
The throttle quadrant was also replaced.
. The scrutiny of maintenance records
revealed that the throttle control module was replaced on VT-ANB in 2019 and 2023.
However, the reason for the replacement was not linked to the fuel control switch. There has
been no defect reported pertaining to the fuel control switch since 2023 on VT-ANB.
revealed that the throttle control module was replaced on VT-ANB in 2019 and 2023.
However, the reason for the replacement was not linked to the fuel control switch. There has
been no defect reported pertaining to the fuel control switch since 2023 on VT-ANB.
4 users liked this post.
Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
July 13, 2025, 00:24:00 GMT
permalink Post: 11920958
Takeoff thrust loss
With about 10 seconds between to-Cutoff and back-to-Run, it.is hard to see recovery with any terrain or obstacles present. Perhaps, assuming accidental Cutoff, they were restored within a second or two, the Quick Relight could have restored thrust rapidly as the engines were still spooling down - then it is a matter of the built-in margins in the takeoff performance. But the report said the engines both were sub-idle when the Quick Relight logic would have reactivated with the restoration to Run.
I doubt it was close - up to 10 seconds with 100% thrust loss. It could easily be evaluated in a Simulator, but not sure it matters now.
2 users liked this post.
Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
July 13, 2025, 00:38:00 GMT
permalink Post: 11920965
Fire handles - lockout
Just a thought \x97 the fire extinguisher handles perform the same function as the fuel cut-off.
Could there have been a strap /booklet or something else that accidentally got under the fire handles and activated them when one of the pilots pulled on the item?
The fire handles are not particularly well protected against something getting underneath them
Is there any information on whether the fuel cutoff switches and fire handles register as separate events on the flight data recorder, or if both are logged under a common indication, such as 'fuel switch cut off'?
Could there have been a strap /booklet or something else that accidentally got under the fire handles and activated them when one of the pilots pulled on the item?
The fire handles are not particularly well protected against something getting underneath them
Is there any information on whether the fuel cutoff switches and fire handles register as separate events on the flight data recorder, or if both are logged under a common indication, such as 'fuel switch cut off'?
1 user liked this post.
Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
July 13, 2025, 00:49:00 GMT
permalink Post: 11920969
But there was electrical power to the switch.
7 users liked this post.
Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
July 13, 2025, 01:05:00 GMT
permalink Post: 11920974
FCS poles
It is worth remembering that each switch has 4 poles. Think of a pole as a section of the switch. Each section controls a different function - reporting switch position to FDR, fuel cut off and so on. The chances of anything other than real physical switch movement (whether it be spilt liquid, wiring damage, loose canon plug or whatever) changing the status of all 4 sections is impossibly small. Then you have two switches.
Last edited by Alty7x7; 13th July 2025 at 01:48 .
Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
July 13, 2025, 01:51:00 GMT
permalink Post: 11920984
Would not expect an FDR dedicated pole. They
might
pull the FCS position from the FADEC, since what really matters is what the FADEC receives as a command. I would expect two poles dedicated to the two circuits, one routed to each FADEC channel, and the others to the non-FADEC-reset-command functions.
Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
July 13, 2025, 02:20:00 GMT
permalink Post: 11920987
My recollection is that the fire handle will be locked in this circumstance, unless the respective fuel control switch is at Cutoff. Engine fire procedure (and not before 400 ft AGL) is fuel control switch to Cutoff and then pull the fire handle (turn left for bottle 1, turn right for bottle 2).
2 users liked this post.
Reply to this quoting this original post. You need to be logged in. Not available on closed threads.