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Hedge36
July 12, 2025, 18:28:00 GMT permalink Post: 11920733 |
Question:
What messages, if any, are displayed on-screen when the fuel cutoff switches are re-positioned (especially to OFF)? I'm wondering if the pilot who asked about the shutoff SAW the other pilot manipulate the switches or if he was alerted by a message... or perhaps he looked down at rollback and realized they were in the OFF position. |
KSINGH
July 12, 2025, 18:37:00 GMT permalink Post: 11920741 |
as per the report- at *most* 1s apart, particularly significant given that it has been mentioned the recording interval of the DFDR is 1s
also I don\x92t know if we\x92ve had an adequate answer to the fact of what data streams the DFDR records, was it only detecting the electrical signal of fuel cut off or the actual position of the toggles- I don\x92t believe it would be the latter which opens an entirely different rabbit hole |
X-37
July 12, 2025, 18:46:00 GMT permalink Post: 11920744 |
A question from an accepted standpoint of relative ignorance - neither a pilot nor hugely familiar with 787s although have spent a lot of time around both.
The accident report indicates that the aircraft had a STAB master caution warning on the previous sector. A maintenance action took place during the turnaround in AMD before the accident flight. Noting that the two guarded stab cutoff switches are directly adjacent to the two guardedfuel run/cutoff switches at the base of the throttle quadrant, is there any condition that could have led a pilot to reach for the stab cutoff at the critical moment? Recurrence of the tech defect from the previous sector or switches being left in the wrong position but not noticed under the red guards ? If that\x92s possible then accidental action of the fuel cutoff switches when the intent was some intervention with the stab switches seems more likely than a wilful pilot action to cut off fuel flow. Is that remotely possible, given the defect history? |
BraceBrace
July 12, 2025, 18:54:00 GMT permalink Post: 11920749 |
Question:
What messages, if any, are displayed on-screen when the fuel cutoff switches are re-positioned (especially to OFF)? I'm wondering if the pilot who asked about the shutoff SAW the other pilot manipulate the switches or if he was alerted by a message... or perhaps he looked down at rollback and realized they were in the OFF position. I believe (long time ago experience) there is an EICAS alert popping up when the fuel control switches are moved to cutoff. However, Boeing has a philosophy of "inhibits" below 400ft the aural alert indicating an EICAS has popped up is one of them. So as PF you would have to look at the EICAS during rotation, read the alert, then look down at the switches instantly. |
sevenfive
July 12, 2025, 19:21:00 GMT permalink Post: 11920769 |
I don\x92t know if the FDR measures the switch position or the electrical signal. The latter is probably more likely, although there has been much discussion around potential scenarios involving accidental switch movement as well as possible causes of electrical glitches. Let\x92s assume that the switches were actually moved, and ignoring the \x93bad faith\x94 scenario, we need a situation that encompasses the switches being moved to Cutoff by one pilot, this action being queried by the other pilot and denied by the pilot who moved the switches.
For consideration, here is a possible scenario that hasn\x92t been mentioned yet and encompasses the frailty of human performance. The report mentions that the flight crew on the immediately prior flight had written up a "STAB POS XDCR" status message, and that troubleshooting was carried out. I wonder if the scenario could be that the accident crew received a Stabiliser EICAS message on or around take-off and the Capt (who was PM) decided to action the first checklist item immediately from memory, by intending to move the Stab switches to Cutoff but moving the fuel switches instead. As in all modern Boeings, the Stabiliser Cutoff switches are immediately next to the Fuel Cutoff switches and operate in the same sense (i.e. down for Cutoff). They are guarded and never normally moved but, with an intent to move the stab switches, \x93muscle memory\x94 (cerebellum activation if you prefer) may have taken the Captain\x92s hand to the Fuel switches, which are operated on every flight. The FO (who is PF) is manually flying at this stage sees and queries it. The Capt denies it, as he doesn\x92t realise what he has done (confirmation bias perhaps). After a few seconds, the terrible mistake is realised, and the fuel switches are moved back to run, but sadly too late and the Capt makes a Mayday call. Perhaps a bit of a stretch but not as much of a stretch as many of the other scenarios in this thread. I think it is a real possibility. Sadly, the only other explanation that I can see is the deliberate \x93bad faith\x94 scenario, which we would all hope is incorrect. Fly Safe PJ88 |
njc
July 12, 2025, 20:18:00 GMT permalink Post: 11920807 |
as per the report- at *most* 1s apart, particularly significant given that it has been mentioned the recording interval of the DFDR is 1s
also I don\x92t know if we\x92ve had an adequate answer to the fact of what data streams the DFDR records, was it only detecting the electrical signal of fuel cut off or the actual position of the toggles- I don\x92t believe it would be the latter which opens an entirely different rabbit hole Regarding your second point: it has been noted by multiple posters that "the actual position" of the switch is a fairly meaningless concept for the EAFR data if you want to exclude the electrical signal arising from the switch itself. So I have to ask: what would you regard as a measurement of the "actual position of the switch", in this context? |
Engineless
July 12, 2025, 20:34:00 GMT permalink Post: 11920817 |
The accident report indicates that the aircraft had a STAB master caution warning on the previous sector. A maintenance action took place during the turnaround in AMD before the accident flight.
Noting that the two guarded stab cutoff switches are directly adjacent to the two guardedfuel run/cutoff switches at the base of the throttle quadrant ,
Since some posters seem focused on the theory that the fuel control switches didn't move - just the electric output did (and as I posted earlier, the FDR only knows electrical states, there is literally no other way for the FDR to monitor the switch position).
So I did a little thought experiment. Uncommanded engine shutdowns (for all causes) are already rare - a 10-6 event. Now, during my 40 year career, I can't remember ever encountering a case where the fuel shutoff was commanded without a corresponding movement of the fuel switch. However in this industry it's a good idea to 'never say never', so let's assume it's happened. It would take something like a hot short to cause it to happen ( moving the voltage from RUN to CUTOFF ) since an open circuit will simply leave the valves where they were. That would put its probability way out there - something like 10-8/hr.
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 I would suggest starting with the maintenence engineer/crew who found 'no fault' after the STAB master caution was investigated immediately prior to this tragic flight. It would not be the first time that 'maintenance' caused an incident... Also, I urge you all to consider how many accidents have been blamed on 'pilot error' (how convenient when billion-dollar companies are at risk) only for further information to come to light that then exonerates the pilots (these stories don't usually make the front page). Try to stay open-minded folks. The investigation has a very long way to go. |
T28B
July 12, 2025, 20:49:00 GMT permalink Post: 11920823 |
(The above posted as neither mod nor admin, to be clear). |
remi
July 12, 2025, 21:17:00 GMT permalink Post: 11920838 |
I believe the *inspection* was not conducted, and whether there was a fault with the configuration of the switch on the accident aircraft is not answered in the report. If pilots were able to move this aircraft's cutoff toggles without lifting them, it seems that might have been reported at some point during its service. But then again, maybe the difference in operation between a correctly configured switch (requires lift to toggle) and incorrectly configured one (does not require lift, but lifting it still works as expected) is not noticeable. I'd be curious to know if India Air has (finally) inspected these switches in their fleet since the accident. |
DTA
July 12, 2025, 21:20:00 GMT permalink Post: 11920839 |
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.
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nachtmusak
July 12, 2025, 21:31:00 GMT permalink Post: 11920849 |
First, 10 seconds is not a long time. Second, I don't know where you are getting the idea that there was a 10 second gap between the pilots noticing or asking 'why did you cut off' and the switches being reset, because the report doesn't give a timestamp for either exclamation from the pilots. It may well have only been a couple of seconds between them noticing and resetting them, the report simply doesn't give that detail.
The truth will be in what was said after 'I didnt', but that's conspicuously absent from the report. Of course deliberate pilot sabotage has occurred in the past, nobody is disputing that. But personally I'm aware of far more cases of pilot mistakes without malice as the root cause of an accident than of all the confirmed and possible cases of sabotage put together, and I'm sure that there are even more cases of the former that I've never heard about (and I don't mean pilot error in general, I'm referring to things like e.g. taking off with an improper configuration). I think people are not actually thinking through how the situation would play out IF it was an honest mistake. Ten seconds is no time at all for either pilot to: - notice the degrading performance (and/or warnings) - scan the instruments and controls for the problem - see (on their display and confirm on the pedestal) that fuel has been cut off - ask the other pilot why they did that (because neither pilot would believe they were the one who did so - that is how action slips work) - get a response that they did not (again, see above) - snap out of confusion and actually do something about the situation Pilots have reacted with far less alacrity in plenty of accidents (even in cases where the day was ultimately saved) and it was not my impression that the aviation industry accused them of criminal intent for it. Surely there is a middle ground between robotic hyper-competence and literal murder? Don't get me wrong, there is a solid chance that it turns out to have been the deliberate murder of hundreds of people. But to me at least it seems extremely uncharitable to confidently declare that that's what happened off a very loose timeline, or to paint people who are considering the possibility of a mistake as just hiding from the truth. |
Engineless
July 12, 2025, 21:42:00 GMT permalink Post: 11920857 |
Like I said,
if you take the preliminary report version of cockpit dialog at face value
, then if the fuel cutoff toggles were never physically turned off maybe they were not physically turned back on. Immediately prior to this flight the pilots reported a STAB master caution, which was investigated but 'no fault' was found. Intermittent electrical fault? Software/logic problem? Stranger things have happened. At least one maintenance engineer would have been in the cockpit immediately prior to this flight. The actions taken by this person(s) should also be part of the investigation.
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PC767
July 12, 2025, 21:47:00 GMT permalink Post: 11920865 |
Ladies and Gentlemen
The situation is simply that a human hand moved the fuel switches for reasons unknown. I clung on to the very thin chance that the reason could have been electrical with words such as 'transition', but tdracer's last post extinguished that slim posibility. From day one I have assumed the loss of thrust on both engines and that the only logical explanation could be fuel cut off switches. I've been a pilot for over 35yrs, 12 of which as a paid professional and around airlines in my earlier iteration as cabin crew. Book ending my aviation career I've been in law, as an investigator and now examininer of facts. There is a strong possibility that it will never be established why the switches were moved. My community/previous community will take the liability for this incident, I'd wager something or other on that. If there is ambiguity or a dearth of evidence to be challenged, the easiest target will be the pilots. The reputations of Boeing and Air India will be saved. At this time there is very little technical detail to be discussed on what happened and how it happened. Until either a substantive leak, a further report or the final report is out, I'm out of the thread. I'd suggest many others have the same patience. |
mh370rip
July 12, 2025, 21:55:00 GMT permalink Post: 11920870 |
A query, the FO was pilot flying and the Captain was pilot monitoring. Is it SOP that pilot flying sits in the LHS at takeoff? As I understand it the situation on power failure is that the battery backup will keep the displays alive until the APU comes online but only on the LHS. Trying to maintain best gliding performance and look for best landing site without any instruments to show speed or attitude would be more difficult. Captain taking over and swapping roles at 200 feet mid crisis is disruptive. 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. |
verticallimit
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'? |
MikeSnow
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. |
Homebrew1
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.
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B2N2
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. |
Alty7x7
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'? |
Alty7x7
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 . |
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