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nomess
July 13, 2025, 13:34:00 GMT permalink Post: 11921328 |
I still think that one of the most puzzling things from the Preliminary Report is the 4 second gap between Engine 1 fuel cutoff switch being returned to RUN, and that of Engine 2. It seems generally agreed one second is a reasonable time to operate both switches, so why did it take so long to move the 2nd switch?
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flyingchanges
July 13, 2025, 14:02:00 GMT permalink Post: 11921342 |
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. |
Easy Street
July 13, 2025, 14:11:00 GMT permalink Post: 11921348 |
I still think that one of the most puzzling things from the Preliminary Report is the 4 second gap between Engine 1 fuel cutoff switch being returned to RUN, and that of Engine 2. It seems generally agreed one second is a reasonable time to operate both switches, so why did it take so long to move the 2nd switch?
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AirScotia
July 13, 2025, 14:27:00 GMT permalink Post: 11921357 |
On the site that I maintain that covers this thread here:
https://paulross.github.io/pprune-th...171/index.html
I removed the subject that described deliberate action on the part of the pilot(s) for reasons I explained here:
Air India Ahmedabad accident 12th June 2025 Part 2
I would restore that subject if any hard evidence appears that suports that theory, not on the basis of speculation (and out of respect to the families and memories of the flight crew). For those thinking along those lines could I offer this challenge: All the civil aviation pilot suicide cases that I have heard about have been achieved by a rapid descent from cruising altitude. It is a pretty sure outcome. But to switch off the fuel just after takeoff, would you really expect that to succeed? Supposing the other pilot noticed and corrected this in one or two seconds rather than ten, then you would have failed. I'm not saying people intent on this behaviour are being rational but even by the laws of un-rationality it seems an unlikely way of trying to achieve your goal. There are only two parts of the flight where the PF's attention will be entirely focused in front of him - takeoff and landing. Cutting the fuel switches on landing is pointless - the plane will in all likelihood land safely as a glider. Above a certain altitude after takeoff, there will be time for the PF to recover the situation. Doing it as soon as the wheels have left the ground pretty much guarantees a crash. Doing it in cruise - FO off to the toilet etc. - it will be obvious which yoke was the one doing the pushing, unless of course you switched seats when your colleague left. The fuel switches are effectively anonymous. |
double-oscar
July 13, 2025, 14:45:00 GMT permalink Post: 11921364 |
It would have been useful if more of the CVR data had been released so as to see the crew interaction. Also the language used on what was released seems to refer to a third person.
However, from an operator perspective. Captain PM, FO PF. PF selects TOGA and follows the thrust levers, Captain confirms Thrust Set and replaces FO hands on the Thrust Levers. 80Kt call by PM, acknowledged by PF. Aircraft calls V1, Captain should withdraw hands from Thrust Levers and calls Rotate at Vr. PM is looking for confirmation the aircraft is climbing and calls Positive Rate. PF confirms and calls Gear Up. At this point the PF will be looking through the HUD looking to follow the flight director, the PM would be checking LNAV had engaged and at 400\x92 checking THR REF and VNAV SPD. However, at this point a loss of thrust occurred. So how was this apparent to the PF who would have been looking out with both hands on the control wheel. Reduction in pitch? GPWS call-out? Decreasing N1 on the engine instruments? EICAS ENG SHUTDOWN? What did the PM see? Who called out the situation? Were any actions called for? At some point as the generators went off line all the FO instruments would have blanked. Did the Captain assume control? I don\x92t think I would have been thinking about the Fuel Cut-Off switches at that point, yet they were specifically mentioned which does mean the switches were moved and it wasn\x92t some internal fault. Hopefully, as the CVR is further analysed some more information will come to light. |
katekebo
July 13, 2025, 14:49:00 GMT permalink Post: 11921371 |
I just read this on avherald.com, and I haven't seen this being discussed here (I may have missed it, in which case please delete my post)
On Jul 12th 2025 (UTC) India's media report that the investigation is NOT focussing on a human action causing the fuel switches to appear in the CUTOFF position, but on a system failure. Service Bulletins by Boeing issued in year 2018 recommending to upgrade the fuel switches to locked versions to prevent inadvertent flip of the switches, as well as the FAA/GE issued Service Bulletin FAA-2021-0273-0013 Attachment 2 relating to loss of control issue (also see above) were NOT implemented by Air India. The stated MN4 computer with faulty soldering, that might weaken and lose contact due to the thermal stress after a number of cycles, interprets data and commands fuel metering valves - with the lost contact attaching the MN4 processor to the EEC intermittent electrical contact, loss of signal processing and engine control faults can occur. The SB writes under conditions for the SB: "An LOTC (Loss Of Thrust Control) event has occurred due to an EEC MN4 microprocessor solder ball failure." According to discussions in the industry it may be possible with the number of cycles VT-ANB had already completed, the solder balls were weakened sufficiently to detach the MN4 from the EEC momentarily due to loads during the takeoff rotation leading to the loss of control of thrust and shut down of the engines. I had a quick look at the SB and it refers to a computer mounted directly on the engine. I find it extremely unlikely that BOTH computers on two different engines might fail simultaneously. So I take this latest information with a grain of salt ("India's media report"). Last edited by katekebo; 13th July 2025 at 15:01 . |
skippybangkok
July 13, 2025, 15:02:00 GMT permalink Post: 11921377 |
With the greatest respect, I don't think any deliberate act has been proven. Allocating blame on assumptions should be avoided. People should work on facts, and then unconfirmed assumptions.
The only known fact is that engines for some reason were shut down. The other known fact is that there is a recorded indication that the start lever command was recorded as both cutoff in short succession then followed by idle detent causing a restart attempt. I think the key unknowns here are important. 1. Was the start lever position recorded, or only the electrical signal? My money is on an electrical signal not position, therefore the manual positioning of the start levers is not conclusively proven. 2. The bulletin for locking mechanism for the start levers has been mentioned in the preliminary report. This is a huge unknown. Did that mean that in a failure that the levers could both move into cutoff at the same time? This occurred exactly as the aircraft was rotating and increasing pitch. 3. The information from the CVR if taken at face value must not be discounted. No pilot actually confirmed conclusively seeing the other move the switch. This could have been an assumption noticing an engine failure, seeing the start levers positions in cutoff or indeed seeing the start levers moved deliberately. This is a huge critical unknown. 4. One pilot asked 'why did you cutoff' and the other responded 'I didn't'. This is not a confirmation of anything for sure. In fact it is equally a suggestion nobody pilot moved the switches as it is saying they did. This is not conclusive. This raises an important question, was this genuine, did either pilot have any reason in their life to attempt to do this and then cover their actions? There is zero suggestion here either way, but hopefully investigators will already be looking at their backgrounds and state of affairs. 5. There is no indication who or what commanded the engines back to idle detent again. There is proof of both engines attempting to restart. I would take this as confirmation of teamwork existing on the flight deck, and this would suggest a lack of deliberate interference by either pilot. Should that have been deliberately done, so much more could have happened. It just hasn't been alluded to in the preliminary report. My own impression is that it did not appear to be a situation of a deliberate act to crash. I say this as they appear to have both tried to save the aircraft and immediately restart the engines and recover taking some critical timely actions demonstrating competent reaction. The timing of the commanding fuel to cutoff os critical imo. The aircraft was pitching. If an accidental command to cutoff occurred then I feel this however unlikely would have been made instead of another action. The only likely thing happening at that exact time or due 2-3 seconds after lift off was gear up. The CVR and recorded timing of engine failure in relation to that challenge and response in SOP will be key imo. Did the challenge for gear up occur before the idle detent electrical signals? Also, the focus should be on that bulletin for the locking mechanism for the start levers. I just cannot imagine an experienced crew doing this by accident and the information just doesn't suggest a deliberate act. My post is just to highlight huge lists of unknowns. The media appears to have made their mind up that the flight crew did this. I just highlight that is definitely not confirmed yet. We have a whole list of unknowns and conflicting communication that raises more questions than they solve. I would urge zero conclusions be made, and RIP the crew and passengers. There are zero conclusions to what happened yet in my opinion, and I think the suggestion to relatives of the flight crew and families tragically killed that this is a known pilot deliberate action simply cannot be made at this point. We must not blame the flight crew prematurely or pretend we know what happened. I think the media should take note and back off from all the assumptions. Kudos to the crew for trying to re-light the engines so quickly. My 10 cents is on the switches and there is not a aireworthiness directive out there for nothing. |
mh370rip
July 13, 2025, 15:03:00 GMT permalink Post: 11921378 |
I just read this on avherald.com, and I haven't seen this being discussed here (I may have missed it, in which case please delete my post)
On Jul 12th 2025 (UTC) India's media report that the investigation is NOT focussing on a human action causing the fuel switches to appear in the CUTOFF position, but on a system failure. Service Bulletins by Boeing issued in year 2018 recommending to upgrade the fuel switches to locked versions to prevent inadvertent flip of the switches, as well as the FAA/GE issued Service Bulletin FAA-2021-0273-0013 Attachment 2 relating to loss of control issue (also see above) were NOT implemented by Air India. The stated MN4 computer with faulty soldering, that might weaken and lose contact due to the thermal stress after a number of cycles, interprets data and commands fuel metering valves - with the lost contact attaching the MN4 processor to the EEC intermittent electrical contact, loss of signal processing and engine control faults can occur. The SB writes under conditions for the SB: "An LOTC (Loss Of Thrust Control) event has occurred due to an EEC MN4 microprocessor solder ball failure." According to discussions in the industry it may be possible with the number of cycles VT-ANB had already completed, the solder balls were weakened sufficiently to detach the MN4 from the EEC momentarily due to loads during the takeoff rotation leading to the loss of control of thrust and shut down of the engines. AD 2021-15-05 requires initial and repetitive replacement of the full authority digital engine control (FADEC) integrated circuit (MN4) microprocessor. The MN4 is part of the FADEC in the engine, the probability of both engines having identical unrelated failures at the same time is very unlikely. Edited: I see katekebo has already raised this as very unlikely Last edited by mh370rip; 13th July 2025 at 15:05 . Reason: Duplicate of a previous poster |
galaxy flyer
July 13, 2025, 15:22:00 GMT permalink Post: 11921391 |
The graph based on the preliminary timeline would indicate 2-3 seconds to establish the RAT power. Having used RATs in the sim and on test flights on two types, that\x92s seems correct. It\x92s very quick and, if the switches were cutoff on the runway, no way would the plane achieved that flight path, probablt overrun the runway.
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oceancrosser
July 13, 2025, 15:35:00 GMT permalink Post: 11921397 |
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. The left and right engine wiring is physically isolated from the other engine - nothing gets routed in common bundles between the engines. Hence there is simply no way a localized issue could affect both engine's wire bundles. So we're talking two independent events that cause the switch output to electrical change state between RUN and CUTOFF without associated switch movement. So now were out in a 10-16/hr. territory. Now, these independent events both occur a second apart - 3,600 seconds/hr., so we've just added ~8 orders of magnitude to the dual failure probability number (10-24/hr.). Now, they both somehow return to normal withing a few seconds of each other - another ~8 orders of magnitude so we're talking 10-32. That means the probability of this happening at any time since the Big Bang is way less than one.... Space aliens look reasonable in comparison. So can we discuss things that might actually have happened? Now my operator had an incident on a 757 in cruise about 10 years ago where the spar valve closed without command. The SPAR VALVE light will probably have lit up (can\x92t remember) but the engine died. From crz thrust to no thrust in seconds. So such things are not unknown. |
hec7or
July 13, 2025, 16:06:00 GMT permalink Post: 11921408 |
If the intent was suicide, in order to make the situation unrecoverable, pulling both fire handles would be the next item to ensure the engines would not restart in the time available, therefore if only the run/cutoff switches were moved to cut off, then the situation was not foreseeably unrecoverable and can only questionably be construed as a suicide.
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Chiefttp
July 13, 2025, 16:37:00 GMT permalink Post: 11921435 |
Three points,
1. One previous poster who was a test pilot stated that the Boeing switches were unguarded, and as such, wouldn’t pass military standards. I flew 4 Military aircraft in the USAF, and none of them had guarded switches or covers over the start /stop switches. They were all toggle type levers or solenoid operated buttons. Perhaps he was referring to RAF aircraft. 2. As far as the previous issue with the Stab Trim. Those switches are guarded and covered, however! I find it hard to believe any stab trim runaway would be detected so early in the flight. I’ve had a runaway stab trim in a 757 and it took a while to diagnose it and finally disconnect the errant trim module. The first indication was the aircraft required more trimming than normal. Nothing one can detect 10 seconds into a flight. 3. I’ve been flying Boeings for over 30 years, (727,757,767) with similar fuel control switches and I can’t think of a single time it was loose, slipped, or faulty. |
TURIN
July 13, 2025, 17:02:00 GMT permalink Post: 11921451 |
If the guards to the stab trim switches were left open by maintenance, I could see a situation in which muscle memory might lead to closing the adjacent fuel control switches. This would also explain the "I didn't do it response", as he believed he was merely closing the guards instead.
When trouble shooting, it normally resets through a BITE test. I don't remember ever having to touch the stab cut off switches as part of line trouble shooting. The aircraft is on a turnaround, if the test doesn't clear the message further trouble shooting may be lengthy, most airlines would want the aircraft dispatched in accordance with the MEL. Deactivating the relevant transducer involves entering the stab bay, disconnecting a plug and writing up the deferral. If it's true, as someone above suggested, that the aircraft was signed off an hour before departure, that is not last minute by the way, then I would guess that the BITE test cleared the message. |
slast
July 13, 2025, 17:15:00 GMT permalink Post: 11921459 |
Just to endorse CaptainBiggles101 post #557. Speculation based on this preliminary report should not start encouraging the simplistic mass media attitude of \x93we don\x92t know what happened so it must be pilot initiated\x94, Don't put together complicated theories about potential sequences of crew actions to give that an air of authority.
We have a very limited initial report which meets the ICAO requirement to produce one. It may or may not be written in the investigators and/or authors\x92 native language, and will have been the subject of considerable \x93negotiation\x94 before release as to its contents. While the bald facts are stated, some cannot be taken at face value without much more context. For example the use of the word \x93transitioned\x94 rather than \x93moved\x94 or \x93placed\x94 in regard to the fuel switches positions may be significant. There is a summary of only two elements of intra-crew voice communications, which again may or may not be in the right language, and one radio message, as yet unattributable to individuals. Everyone here should know that there are many missing elements which could be just as significant. It\x92s highly regrettable that even \x93reputable\x94 media use such summaries and extracts in headlines and jump to simplistic conclusions. The complete story may be totally different and follow an extremely improbable sequence of events. This is nothing new - for example forty years ago the BBC\x92s first broadcast report of the crash of JAL 123 B747 included a statement that first information indicated it to be \x93almost certainly the result of pilot error\x94. I was the ranking IFALPA spokesman at the time and quickly got this removed from their reports with a later apology from the head of BBC news. The accident was actually due to catastrophic structural failure following an inadequate repair of a tail-strike 7 years earlier, and the crew had struggled heroically for 30 minutes to keep an a physically unflyable aircraft airborne. I mention it simply to illustrate that professionals here should do as little as possible to feed unverifiable conclusions, and follow the mods guidance. Rant over. Steve |
B2N2
July 13, 2025, 17:21:00 GMT permalink Post: 11921462 |
A purely speculative technical question.
If you were faced with that scenario (assuming accidental cut-off of both engines) if you shoved the nose down and retracted the gear would it buy you enough time for at least one engine to have come back online sufficiently to save the day or was a crash innevitable? Given a different set of circumstances at some point the situation is unrecoverable and you become \x93dead man walking\x94. Stalls, spins, unusual attitude recovery, MCAS events, they all become unrecoverable below a certain altitude. If I had to take a guess I would say 2500-3000\x92 AGL and this could have been recoverable. |
Winemaker
July 13, 2025, 17:37:00 GMT permalink Post: 11921474 |
A bit of psycology. If one were intent on crashing the plane and did switch to cut off, they would most likely fight like hell to keep them off.
Kudos to the crew for trying to re-light the engines so quickly. My 10 cents is on the switches and there is not a aireworthiness directive out there for nothing. edit: Sorry, didn't see Andy S post..... |
fdr
July 13, 2025, 17:40:00 GMT permalink Post: 11921477 |
Hi,
I have a couple of questions. Forgive me for being late into this thread if any of them is already discussed: 1) I just read this in a Boeing manual:
The fuel control switches send signals to open or close fuel valves to operate or shutdown the engines.
There seems to be RDC's (remote data concentrators) and CDN (common data network) between those fuel switches and the fuel valves. Is there any possibility that there may have been an electronic control module or sensor fault to generate such a signal rather than mechanical switch movements?
- They send signals to the remote data concentrators (RDC) and the spar valve start switch relays. - The spar valve start switch relays use these signals to control the spar valve and the high pressure shut off valve (HPSOV) in the fuel metering unit (FMU). - The RDCs send the signals to the common data network (CDN) and then to the electronic engine control (EEC) to operate the FMU fuel valves (FMV and HPSOV). The fuel control switches have 2 positions: - RUN - CUTOFF. You must pull the switch out of a detent to select a position. 2) Looking at the incident timeline, one of the pilots takes corrective action to reswitch to RUN position 10 seconds after maximum air speed is reached and 5 seconds after RAT is deployed. Is this normal? It's not clear however that whether their conversation is after or before the RAT is deployed. (No visual or auditory cues in the cockpit for a critical fuel switch action? Not hearing the engines shutting down?) 3) The same pilot that turns on Engine 1's fuel switch, turns on Engine 2's switch 4 whole seconds later. Why not consecutively, right one after the other, just like they were turned off one second apart? If only he had done so the second engine might have recovered in time as well. 4) This aircraft's TCM has been replaced in 2019 and 2023, not related to a fuel switch issue. And there had been no fuel switch defect reports since 2023. One begs to ask if there had been a fuel switch defect report back in 2023 and what was the nature of it? Are TCM's replaced as a whole, including the switches, twice? If so, why wouldn't they install a TCM version at least in 2023 with redesigned switches (w/ enhanced locking mechanism) mentioned in the FAA SAIB? Have they installed old/used TCM's manufactured prior to 2018 SAIB? Please note that the RH and LH GE engines of the aircraft were only installed in March 2025 and May 2025 respectively, but they were used and dating from 2013 and 2012. Is this normal for a 12 year old Boeing aircraft to change so many mission critical components? Electronic parts somehow, but how durable are those GE engines? Thanks, C.A. When reading any of the data when it comes out, pay some attention to the sampling rate of the data being provided, it is quite possible to make erroneous assumptions where that is not taken into consideration. The data buses used to get data from the aircraft system to the recorder, and the recorders themselves use sequential sentences, and varyious rates. IMHO. |
EXDAC
July 13, 2025, 17:45:00 GMT permalink Post: 11921482 |
- They send signals to the remote data concentrators (RDC) and the spar valve start switch relays.
There seems to be RDC's (remote data concentrators) and CDN (common data network) between those fuel switches and the fuel valves. Is there any possibility that there may have been an electronic control module or sensor fault to generate such a signal rather than mechanical switch movements?
- The spar valve start switch relays use these signals to control the spar valve and the high pressure shut off valve (HPSOV) in the fuel metering unit (FMU). (snip) "They send signals to the remote data concentrators (RDC) and the spar valve start switch relays." Nothing in what you quoted says or implies that the RDC is in the fuel valve control path. Edit to add - The RDC is in the path that feeds fuel switch position to the flight data recorder. Any error in that path could make the recorded switch position disagree with the actual switch position. It cannot change the state of the fuel valves and it cannot cause the engines to stop producing thrust. |
andihce
July 13, 2025, 18:03:00 GMT permalink Post: 11921493 |
Electrical effects of engine rollback
As I understand it from previous discussions, without the APU, all electrical power except for that DC power provided by battery to essential systems would have been lost. With the copilot as PF, would he have lost his instrument displays? If so, possibly additional startle effect and workload for him. Why did the ADS-B information keep going on for so long? My understanding from previous threads was that loss of ADS-B was considered an indication of loss of electrical power. What else would be expected with loss of power? Some general speculation: I find it hard to understand the long delay from what must have been the onset of obvious issues to the time the first engine is set to "RUN". I wonder if much more cockpit dialog intervened, e.g. PF requesting PM to turn the fuel switches back on (since he had his hands full), and eventually operating the switches himself, with the delay and time gap between the two switches being turned to "RUN" being attributable to being preoccupied with flying the aircraft under trying conditions. |
Contact Approach
July 13, 2025, 18:03:00 GMT permalink Post: 11921494 |
It would have been useful if more of the CVR data had been released so as to see the crew interaction. Also the language used on what was released seems to refer to a third person.
However, from an operator perspective. Captain PM, FO PF. PF selects TOGA and follows the thrust levers, Captain confirms Thrust Set and replaces FO hands on the Thrust Levers. 80Kt call by PM, acknowledged by PF. Aircraft calls V1, Captain should withdraw hands from Thrust Levers and calls Rotate at Vr. PM is looking for confirmation the aircraft is climbing and calls Positive Rate. PF confirms and calls Gear Up. At this point the PF will be looking through the HUD looking to follow the flight director, the PM would be checking LNAV had engaged and at 400\x92 checking THR REF and VNAV SPD. However, at this point a loss of thrust occurred. So how was this apparent to the PF who would have been looking out with both hands on the control wheel. Reduction in pitch? GPWS call-out? Decreasing N1 on the engine instruments? EICAS ENG SHUTDOWN? What did the PM see? Who called out the situation? Were any actions called for? At some point as the generators went off line all the FO instruments would have blanked. Did the Captain assume control? I don\x92t think I would have been thinking about the Fuel Cut-Off switches at that point, yet they were specifically mentioned which does mean the switches were moved and it wasn\x92t some internal fault. Hopefully, as the CVR is further analysed some more information will come to light. Interestingly ENG 1 was cut off first\x85 |
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