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sorvad
July 12, 2025, 07:42:00 GMT permalink Post: 11920296 |
Timeline of known events with source attribution from the preliminary report:
08:07:33 ATC: Takeoff clearance 08:07:37 A-SMGCS: Aircraft starts rolling 08:08:33 EAFR: V1 153kts 08:08:35 EAFR: Vr 155kts 08:08:39 EAFR: Gnd-Air mode transition 08:08:42 EAFR: Max IAS 180kts, Eng 1/2 Cutoff switches activate within 1 second of each other 08:08:42 CVR: "Why did you cut off", "I did not" (exact time not specified) 08:08:42 A-SMGCS: RAT deployed (exact time not specified) 08:08:47 EAFR: Both engine N2 below min idle. RAT hyd pwr commences 08:08:52 EAFR: Eng 1 cutoff to RUN 08:08:54 EAFR: APU inlet door opens (auto start logic) 08:08:56 EAFR: Eng 2 cutoff to RUN 08:09:05 ATC: Mayday call 08:09:11 EAFR recording stops Fuel cutoff switches operated within 1 second of each other suggests to me that the locking mechanism wasn't working as per (SAIB) No. NM-18-33. Any loose item could have accidentally (or not) operated the switches (including hands). Last edited by sorvad; 12th July 2025 at 08:03 . Reason: Clarification |
Natterjak
July 12, 2025, 07:55:00 GMT permalink Post: 11920310 |
The accident aircraft was written up for a status message of ”STAB POS XDCR” on the previous flight, which is a message relating to implausible data from the stab trim switches. It was released from maintenance (according to the preliminary report) at 06:40UTC ahead of an 07:40UTC departure (the crash flight) with ”no fault found”.
On the 787-8, as all modern planes, switches are not cabled as dry closing contacts all the way from the switch poles to the affected end devices (FADECs in the case of fuel cutoff switches), but rather connect locally to an analogue/digital converter to encode the switch position data onto the digital comms bus ARINC629 which allows all aircraft systems to talk to one another. Are the fuel cutoff switches, which are positioned adjacent to the stab trim switches, connected to the same ADC module which produced the error message on the previous flight, which maintenance was unable to resolve before the accident flight took off? I do not know, but it must be worthy of being looked into. |
Diff Tail Shim
July 12, 2025, 08:18:00 GMT permalink Post: 11920332 |
Spoken to a rated mate whom is current on 78s and he told me that inadvertent operation of a fuel shut off in flight has happened with a switch being knocked past its detent (lock) by the switch being caught by a crew bag.
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sorvad
July 12, 2025, 08:26:00 GMT permalink Post: 11920339 |
Probably not during Takeoff I wouldn\x92t have thought.
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TURIN
July 12, 2025, 08:37:00 GMT permalink Post: 11920352 |
I cannot imagine a situation where any pilot would be moving a crew bag within seconds of getting airborne.
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Musician
July 12, 2025, 08:56:00 GMT permalink Post: 11920377 |
Was the RAT deployed manually?
The report says,
As per the EAFR data both engines N2 values passed below minimum idle speed, and the
RAT hydraulic pump began supplying hydraulic power at about 08:08:47 UTC.
This was 5 seconds after the fuel was cut off.
It suggests to me that the RAT deployment was initiated while the engines were still above idle and generating electrical power. Obviously one of the pilots could have done it via depressing the switch, as it's a "dual engine failure/stall" memory item (see Air India Ahmedabad accident 12th June 2025 Part 2 ) that won't hurt anything. Is there a way for the RAT to deploy while the engines are still above idle? |
dsbery
July 12, 2025, 09:14:00 GMT permalink Post: 11920399 |
When I was a young F/O, some of the captains I flew with had the (annoying) habit of resting their hands just behind the thrust levers on their PM (PNF) sectors to 'be ready' to reject the takeoff. This would put the hands in the vicinity of the Fuel Cutoffs, which would, in turn, increase the chances of an unintended action on these switches. Is this a possibility, or am I way off?
Last edited by Senior Pilot; 12th July 2025 at 09:25 . Reason: Quote |
JPI33600
July 12, 2025, 09:33:00 GMT permalink Post: 11920418 |
Well, speaking of fuel-cut switches, I read
NM-18-33 SAIB
with attention, and as a not-that-fluent english speaker, I stumbled on this sentence (my bold):
If the locking feature is
disengaged
, the switch can be moved between the two positions without lifting the switch during transition, and the switch would be exposed to the potential of inadvertent operation.
And while I was painfully crawling the thread, I noticed the following picture about an "undesirable condition": ![]() Incorrect lock tab position on fuel cut-off switch If this incorrect mounting is actually possible, it would possibly remain unnoticed from the pilots (normal "pull-up then move" action is unaffected), but it would cancel the protective function of the so-called "locking tab", and even limit the travel of the switch handle in both directions, making it more vulnerable to an undesired change of state. The photos above seem convincing enough, but I'd be very grateful for an informed opinion on this assembly mistake. Even if this is possible, the probability of both switches being unexpectedly snapped seems very remote to say the least, but not as remote as previously estimated. |
Mrshed
July 12, 2025, 09:37:00 GMT permalink Post: 11920429 |
As a non pilot, I find this statement in the report interesting (in it's inclusion if nothing else), but I assume that this reference to the replacement module in 2023 (the module including the fuel cutoff switches?) we view as pretty irrelevant to cause?
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. |
DTA
July 12, 2025, 10:26:00 GMT permalink Post: 11920464 |
Well, speaking of fuel-cut switches, I read
NM-18-33 SAIB
with attention, and as a not-that-fluent english speaker, I stumbled on this sentence (my bold):
I could hardly figure what the "disengaged" word meant in this context, so I did a Google search for the switch part numbers (especially "766AT614-3D") to figure the difference between them, and a page from this chinese web site was part of the results. And while I was painfully crawling the thread, I noticed the following picture about an "undesirable condition": ![]() Incorrect lock tab position on fuel cut-off switch If this incorrect mounting is actually possible, it would possibly remain unnoticed from the pilots (normal "pull-up then move" action is unaffected), but it would cancel the protective function of the so-called "locking tab", and even limit the travel of the switch handle in both directions, making it more vulnerable to an undesired change of state. The photos above seem convincing enough, but I'd be very grateful for an informed opinion on this assembly mistake. Even if this is possible, the probability of both switches being unexpectedly snapped seems very remote to say the least, but not as remote as previously estimated. One other useful thing from that web site is a partial schematic which shows the connection of the 4 poles in the switch. I believe this is from a 737NG but it should be the same idea. ![]() |
nachtmusak
July 12, 2025, 10:43:00 GMT permalink Post: 11920474 |
SLF: I have a small observation but I'm not sure what it means or if it has any relevance to the accident.
Previously I had assumed that the ADS-B data cut out at the same time as power was lost, so I imagined that whatever caused the fairly clear loss of thrust would have happened not too long before. But this report throws a bit of a wrench in my understanding of that. According to the report, the fuel cutoff switches transition from RUN to CUTOFF at or very shortly after 08:08:42 UTC. Both engines' N2 values pass below minimum idle speed and the RAT begins supplying hydraulic power at about 08:08:47. Does this not imply that the generators have already been lost? With the APU also being off (the APU inlet door is noted to start opening at 08:08:54), I would have expected ADS-B data to cut out at or before 08:08:47. But curiously FlightRadar24 at least claims to have received data frames from the aircraft until 08:08:51.640970, almost five seconds later and almost ten seconds after the transition to CUTOFF (though the last frame containing coordinates comes at 08:08:50.871005). Could anyone with relevant experience confirm how long it would take for AC power to be lost in this situation? Also, is it usual/unusual for a preliminary report like this to mention if/when the flight recorder switched to its independent power supply? I imagine it would definitely be in the final report, but I'd hoped it would be easily observable enough to be in this one. Beyond idle curiosity I'm asking because the report also says the no. 1 engine's cutoff switch transitioned from CUTOFF to RUN at "about 08:08:52", which oddly coincides with the last ADS-B data frame at 08:08:51.640970, and that seems important somehow. Or more likely I'm just ignorant of some quirk of the 787's electrical system. For reference FR24's CSV containing all ADS-B frames supposedly received from the aircraft can be found in their post here: https://www.flightradar24.com/blog/f...rom-ahmedabad/ |
Uplinker
July 12, 2025, 10:51:00 GMT permalink Post: 11920482 |
"The aircraft achieved the maximum recorded airspeed of 180 Knots IAS at about 08:08:42 UTC and immediately thereafter, the Engine 1 and Engine 2 fuel cutoff switches transitioned from RUN to CUTOFF position one after another with a time gap of 01 sec."
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Someone Somewhere
July 12, 2025, 11:02:00 GMT permalink Post: 11920495 |
The accident aircraft was written up for a status message of ”STAB POS XDCR” on the previous flight, which is a message relating to implausible data from the stab trim switches. It was released from maintenance (according to the preliminary report) at 06:40UTC ahead of an 07:40UTC departure (the crash flight) with ”no fault found”.
On the 787-8, as all modern planes, switches are not cabled as dry closing contacts all the way from the switch poles to the affected end devices (FADECs in the case of fuel cutoff switches), but rather connect locally to an analogue/digital converter to encode the switch position data onto the digital comms bus ARINC629 which allows all aircraft systems to talk to one another. Are the fuel cutoff switches, which are positioned adjacent to the stab trim switches, connected to the same ADC module which produced the error message on the previous flight, which maintenance was unable to resolve before the accident flight took off? I do not know, but it must be worthy of being looked into. I think they're called remote data concentrators - in many cases it is a conversion from a direct digital input to a bus signal; electronics would not call it an 'analog' input unless it was actually measuring a quantitative value.
Was the RAT deployed manually?
The report says, As per the EAFR data both engines N2 values passed below minimum idle speed, and the RAT hydraulic pump began supplying hydraulic power at about 08:08:47 UTC. This was 5 seconds after the fuel was cut off. It suggests to me that the RAT deployment was initiated while the engines were still above idle and generating electrical power. Obviously one of the pilots could have done it via depressing the switch, as it's a "dual engine failure/stall" memory item (see Air India Ahmedabad accident 12th June 2025 Part 2 ) that won't hurt anything. Is there a way for the RAT to deploy while the engines are still above idle? That is a very good question IMHO. |
stickstirrer
July 12, 2025, 11:09:00 GMT permalink Post: 11920505 |
It doesn\x92t explain the reason behind going for the stab cut out switches when the report makes no mention of any stab warning - which surely would be a highly Important event given the closeness of the switches. |
Capn Bloggs
July 12, 2025, 11:32:00 GMT permalink Post: 11920533 |
Originally Posted by
Uplinker
This might have been discussed but as has been suggested upthread; a possible scenario is that at some point, PIC took their hands off the thrust levers and/or placed them in a guarding position behind the thrust levers at their base - but by doing so unfortunately nudged the Fuel cut-off switches to 'Off' - perhaps 'helped' by there either being incorrectly fitted locking mechanisms or worn locking mechanisms ?
Originally Posted by
Uplinker
On this flight, the relative drop in noise and calm that follows the landing gear doors closing after the gear retracts during the initial climb, might have caused an action slip by PIC to perform the engine shut-down procedure used when parking on stand.
Mods, if you don't lock the thread, I'm going back to Facebook! ![]() |
Sailvi767
July 12, 2025, 11:46:00 GMT permalink Post: 11920554 |
Was the RAT deployed manually?
The report says,
As per the EAFR data both engines N2 values passed below minimum idle speed, and the
RAT hydraulic pump began supplying hydraulic power at about 08:08:47 UTC.
This was 5 seconds after the fuel was cut off.
It suggests to me that the RAT deployment was initiated while the engines were still above idle and generating electrical power. Obviously one of the pilots could have done it via depressing the switch, as it's a "dual engine failure/stall" memory item (see Air India Ahmedabad accident 12th June 2025 Part 2 ) that won't hurt anything. Is there a way for the RAT to deploy while the engines are still above idle? |
Seamless
July 12, 2025, 11:49:00 GMT permalink Post: 11920556 |
If the thrust levers were found in idle but, according to the EAFR, were set to TO thrust until the end, doesn\x92t that also raise further questions? I mean: Of course, the impact causes compression at the nose, but the centrifugal forces act in the opposite direction. So, if there is an objective inconsistency here, and we have a pilot who says he did not operate the fuel cut-off switches, while the EAFR indicates otherwise, then we have yet another inconsistency.
![]() Relevant section in the preliminary report |
Mb194dc
July 12, 2025, 12:04:00 GMT permalink Post: 11920568 |
Deliberate pilot action should be ruled out until any evidence and motivation for why that's the case emerges.
All we know is the fuel cut off switches were flipped to Cutoff for 10 seconds and then to run again. Not how or by what. The focus should be on how this could occur. Accidentally, technical malfunction, a foreign object somehow hitting and moving them or other reason? Theories needs to be tested in a cockpit with the exact configuration of this aircraft and with the angles and forces involved as much as we can. It should be possible to simulate it pretty closely and whatever happened should be repeatable. It's going to be something extremely unlikely, or we'd have seen it before in 10 years of 787 service. |
AfricanSkies
July 12, 2025, 12:14:00 GMT permalink Post: 11920575 |
Deliberate pilot action should be ruled out until any evidence and motivation for why that's the case emerges.
All we know is the fuel cut off switches were flipped to Cutoff for 10 seconds and then to run again. Not how or by what. The focus should be on how this could occur. Accidentally, technical malfunction, a foreign object somehow hitting and moving them or other reason? Theories needs to be tested in a cockpit with the exact configuration of this aircraft and with the angles and forces involved as much as we can. It should be possible to simulate it pretty closely and whatever happened should be repeatable. It's going to be something extremely unlikely, or we'd have seen it before in 10 years of 787 service. He didn\x92t say, \x93did you just see that pink elephant fall off the dashboard?\x94 How are you going to \x93simulate something pretty closely\x94 when it\x92s also \x93extremely unlikely\x94? The chance that it was a mechanical or electrical failure of both fuel switches , 2 seconds apart , is for all intents and purposes, zero. Therefore they were moved by hand. |
sarah737
July 12, 2025, 12:47:00 GMT permalink Post: 11920592 |
Deliberate pilot action should be ruled out until any evidence and motivation for why that's the case emerges.
All we know is the fuel cut off switches were flipped to Cutoff for 10 seconds and then to run again. Not how or by what. The focus should be on how this could occur. Accidentally, technical malfunction, a foreign object somehow hitting and moving them or other reason?. |
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