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| Feathers McGraw
July 10, 2025, 16:33:00 GMT permalink Post: 11919132 |
Given that it would have been obvious to the crew very late on that they were going down, might the switches being set to CUTOFF be a last ditch measure to try to prevent a post-crash fire?
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| fdr
July 10, 2025, 16:34:00 GMT permalink Post: 11919133 |
We are on a roll discussing the fuel control switch positions based on unsubstantiated reports which at least meet the stringent requirements of being "rumours". On the basis of those reports and in the vacuum of information, we seem to now be discussing how the fuel control switches function.
I am no longer interested in being a witness to the abuse of anonymity that arises on this thread. cheers The thread is closed so there are no user likes are available. |
| PPRuNeUser548247
July 10, 2025, 16:38:00 GMT permalink Post: 11919135 |
That said, switches found in the RUN position don\x92t generate investigative focus, they're assumed to be where they should be. The mere fact that the fuel switches are attracting attention implies there's something abnormal.
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| tdracer
July 11, 2025, 00:34:00 GMT permalink Post: 11919310 |
This has all been answered in previous posts, but I'll repeat it for those you don't want to look back through something like 150 pages:
Thrust Lever Angle (TLA) is measured directly by the FADEC, using a resolver hardwired to and excited by the FADEC. Both FADEC channels have their own resolver input - on most Boeing aircraft it's a common resolver with two sets of electrically isolated windings, however on the 787 it actually uses two mechanically separate resolvers. The resolver is basically read as "sine" and "cosine" which is converted in the angle. This also makes error detection easy, using the sine squared + cosine squared relationship. Any other aircraft systems that use TLA use the TLA signal relayed back to the aircraft by the FADEC. The fuel control switch is a two-position multiple pole 'latching' switch - you have to pull it out slightly over detent to move it between the RUN and CUTOFF positions (on other aircraft there is an interposing relay for some of the functions. not sure about the implementation on the 787). Moving the switch to cutoff sends a DC signal to both the High Pressure ShutOff Valve (HPSOV) in the fuel control and the spar valve commanding them to close. HPSOV is solenoid actuated and is near instantaneous, Spar Valve takes ~one second to change positions (yes, this is different than some other airframers that only send the signal to one valve or the other, but it's been standard Boeing design practice since the early 1970s). Both the HPSOV solenoid and the Spar Valve are designed to stay in their last commanded position if airframe power is lost. Moving the switch to CUTOFF also sends a 'reset' signal to the FADEC - meaning the FADEC will be offline for roughly one second. On the 787 (and 777 and 747-8), there is a brief pause (~0.25 seconds) before the shutdown signal is sent to the engine to allow the electrical system to reconfigure to prevent a brief interrupt of electrical power to the rest of the aircraft. Pulling the Fire Handle does the same thing as the fuel condition switch - via separate wiring (physically isolated from the fuel switch wiring to help protect from things like rotor burst damage), with the exception of the FADEC reset (since there is no requirement to be able to restart the engine after a Fire Handle shutdown). There is absolutely no TLA input into either the fuel conditions switch or the Fire Handle - you can shutdown the engine via either regardless of Thrust Lever Angle. All this is standard Boeing design practice (and except for the no-break electrical power transfer) has been for at least 50 years. This is enforced by the Boeing "Design Requirements and Objectives" - DR&O - compliance with is demonstrated by an audit after the final design freeze. The thread is closed so there are no user likes are available. |
| inbalance
July 11, 2025, 20:30:00 GMT permalink Post: 11919765 |
From the Report:
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. The Engine N1 and N2 began to decrease from their take-off values as the fuel supply to the engines was cut off.
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. 10 users liked this post. Reply to this quoting this original post. You need to be logged in. Not available on closed threads. |
| KSINGH
July 11, 2025, 20:40:00 GMT permalink Post: 11919771 |
- fuel cut offs were found in the RUN position
- on take off roll both engines lost power as the fuel cut offs went from RUN to cutoff - CVR recorded one pilot asking why they had gone to CUTOFF - within 10 seconds the fuel cutoff was moved back to RUN -RAT was deployed, APU had begun auto start - 32 seconds after Vr the MAYDAY was called This should also dispel a lot of the comments about AAIB-India, Indian culture in general and general competence. For a preliminary report this is far more thorough and extensive than what would normally be expected and they\x92ve kept Boeing, GE, FAA and investigators from US, UK, Canada and Portugal in the loop from the start They have also clarified why it took so long to do the EAFR download- because of the extensive damage they had to source specialist equipment from the NTSB that only arrived on the 23rd of June (they downloaded on the 24th) so all that talk of a \x91coverup\x92 is pretty embarrassing now of course the big question is why/how those switches were commanded into cutoff in the first place the exact sequence at Vr is the most critical, there hasn\x92t been much scrutiny at all that I can see in the Indian/international media of the personal background of the flight deck crew which has happened in other suspected pilot initiated disasters in the past, I guess this is an avenue investigators will have been doing themselves 13 users liked this post. Reply to this quoting this original post. You need to be logged in. Not available on closed threads. |
| Engineless
July 11, 2025, 20:40:00 GMT permalink Post: 11919772 |
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. The Engine N1 and N2 began to decrease from their take-off values as the fuel supply to the engines was cut off. 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 CCTV footage obtained from the airport showed Ram Air Turbine (RAT) getting deployed during the initial climb immediately after lift-off (fig. 15). No significant bird activity is observed in the vicinity of the flight path. The aircraft started to lose altitude before crossing the airport perimeter wall. As per the EAFR, the Engine 1 fuel cutoff switch transitioned from CUTOFF to RUN at about 08:08:52 UTC. The APU Inlet Door began opening at about 08:08:54 UTC, consistent with the APU Auto Start logic. Thereafter at 08:08:56 UTC the Engine 2 fuel cutoff switch also transitions from CUTOFF to RUN. When fuel control switches are moved from CUTOFF to RUN while the aircraft is inflight, each engines full authority dual engine control (FADEC) automatically manages a relight and thrust recovery sequence of ignition and fuel introduction. The EGT was observed to be rising for both engines indicating relight. Engine 1’s core deceleration stopped, reversed and started to progress to recovery. Engine 2 was able to relight but could not arrest core speed deceleration and re-introduced fuel repeatedly to increase core speed acceleration and recovery. The EAFR recording stopped at 08:09:11 UTC 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. RAT in extended position 15 As per the EAFR, the Engine 1 fuel cutoff switch transitioned from CUTOFF to RUN at about 08:08:52 UTC. The APU Inlet Door began opening at about 08:08:54 UTC, consistent with the APU Auto Start logic. Thereafter at 08:08:56 UTC the Engine 2 fuel cutoff switch also transitions from CUTOFF to RUN. When fuel control switches are moved from CUTOFF to RUN while the aircraft is inflight, each engines full authority dual engine control (FADEC) automatically manages a relight and thrust recovery sequence of ignition and fuel introduction. The EGT was observed to be rising for both engines indicating relight. Engine 1’s core deceleration stopped, reversed and started to progress to recovery. Engine 2 was able to relight but could not arrest core speed deceleration and re-introduced fuel repeatedly to increase core speed acceleration and recovery. The EAFR recording stopped at 08:09:11 UTC At about 08:09:05 UTC, one of the pilots transmitted “MAYDAY MAYDAY MAYDAY”. 08:08:42 Engine 1 and Engine 2 fuel cutoff switches transitioned from RUN to CUTOFF position. One of the pilots asks the other why did he cutoff. The other pilot responded that he did not do so. 08:08:52 Engine 1 fuel cutoff switch transitioned from CUTOFF to RUN 08:08:56 Engine 2 fuel cutoff switch also transitions from CUTOFF to RUN Who (or what?) operated the cutoff switches? Last edited by Engineless; 11th July 2025 at 20:53 . 5 users liked this post. Reply to this quoting this original post. You need to be logged in. Not available on closed threads. |
| Kraftstoffvondesibel
July 11, 2025, 20:46:00 GMT permalink Post: 11919773 |
So, yes, switches.
either 1/deliberately cut off by someone in the cockpit, or 2/placed in an intermediate gate position possible due to wear or wrong installation, happens during engine start, and then vibrates or bumps to cut-off during the take off roll or 3/some kind of liquid or other contamination in the LRU shorting both and cycling them after 8 seconds brought them electrically back to RUN. Anyone got other ideas? 5 users liked this post. Reply to this quoting this original post. You need to be logged in. Not available on closed threads. |
| PPRuNeUser548247
July 11, 2025, 20:47:00 GMT permalink Post: 11919775 |
FAA issued an SAIB in 2018 about these fuel control switches being installed without the locking feature engaged\x97Air India didn\x92t act on it (not mandatory).
No evidence of birdstrike, fire, or mechanical failure. Both engines had good health data. The only obvious explanation at this stage is an inadvertent dual shutdown by crew, 7 users liked this post. Reply to this quoting this original post. You need to be logged in. Not available on closed threads. |
| moosepileit
July 11, 2025, 20:52:00 GMT permalink Post: 11919778 |
Ready to talk about the current Embraer method of respective throttle must be at idle to allow the fuel cutoff switch to send a cutoff signal?
That's where I was going in the last page of the last, closed thread. Wear and tear, off by mistake, off by ill-will, off by cockpit FOD flying about at rotation, no effect with throttle forward. Last edited by moosepileit; 11th July 2025 at 21:09 . 9 users liked this post. Reply to this quoting this original post. You need to be logged in. Not available on closed threads. |
| KSINGH
July 11, 2025, 20:53:00 GMT permalink Post: 11919779 |
FAA issued an SAIB in 2018 about these fuel control switches being installed without the locking feature engaged\x97Air India didn\x92t act on it (not mandatory).
No evidence of birdstrike, fire, or mechanical failure. Both engines had good health data. The only obvious explanation at this stage is an inadvertent dual shutdown by crew, then again this isn\x92t all pointing at the pilots which is interesting 6 users liked this post. Reply to this quoting this original post. You need to be logged in. Not available on closed threads. |
| Rarife
July 11, 2025, 20:57:00 GMT permalink Post: 11919787 |
So, yes, switches.
either 1/deliberately cut off by someone in the cockpit, or 2/placed in an intermediate gate position possible due to wear or wrong installation, happens during engine start, and then vibrates or bumps to cut-off during the take off roll or 3/some kind of liquid or other contamination in the LRU shorting both and cycling them after 8 seconds brought them electrically back to RUN. Anyone got other ideas? Reply to this quoting this original post. You need to be logged in. Not available on closed threads. |
| PPRuNeUser548247
July 11, 2025, 20:57:00 GMT permalink Post: 11919789 |
That “I didn’t” on the CVR doesn’t sit right. If the cutoff switch movement was accidental, one would expect shock, confusion, or immediate troubleshooting, not a flat denial.
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| Diff Tail Shim
July 11, 2025, 21:00:00 GMT permalink Post: 11919790 |
FAA issued an SAIB in 2018 about these fuel control switches being installed without the locking feature engaged\x97Air India didn\x92t act on it (not mandatory).
No evidence of birdstrike, fire, or mechanical failure. Both engines had good health data. The only obvious explanation at this stage is an inadvertent dual shutdown by crew, Last edited by Diff Tail Shim; 11th July 2025 at 21:18 . Reply to this quoting this original post. You need to be logged in. Not available on closed threads. |
| digits_
July 11, 2025, 21:05:00 GMT permalink Post: 11919798 |
Not really. It might also indicate that he saw them move, knew his hands were somewhere else, or a plethora of other reasons. Even if one accidentally moves a lever or pushes the wrong button, the first response would likely be denial as well, then followed by an 'oh oops, turns out I did'.
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| wtsmg
July 11, 2025, 21:07:00 GMT permalink Post: 11919802 |
I would look at this from the other way and suggest it doesn't sit right as if someone had just done it deliberately, seconds after rotation, why would they bother denying it, if you see what I mean? 6 users liked this post. Reply to this quoting this original post. You need to be logged in. Not available on closed threads. |
| NWSRG
July 11, 2025, 21:10:00 GMT permalink Post: 11919807 |
10 seconds from challenge to switching the fuel switch back on? Would it not be an immediate act?
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| digits_
July 11, 2025, 21:16:00 GMT permalink Post: 11919815 |
"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." Does anyone know what the sampling frequency of the data is? If we get one readout per second, then it's possible that a one second difference could only be a millisecond difference in real life, which doesn't necessarily rule out an accidental bump. If there truly was a second of difference, there aren't many other options than an intentional act. Not necessarily with the purpose of crashing the plane though (confusion, hallucination, distraction, ..) 9 users liked this post. Reply to this quoting this original post. You need to be logged in. Not available on closed threads. |
| Blacksheep
July 11, 2025, 21:17:00 GMT permalink Post: 11919817 |
I remember the SAIB. I assessed it as “recommended” to all our customers and all agreed. I then raised work orders to check all fuel cut-off switches for the missing locking bar conditions. None were found defective. The preliminary report says the switches were found in the Run position. There is no mention of whether the locking mechanism is correctly in place. We need to wait for the full report for that, as this matter is still under investigation.
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| mh370rip
July 11, 2025, 21:24:00 GMT permalink Post: 11919826 |
What the hell happened in the cockpit?
08:08:42 Engine 1 and Engine 2 fuel cutoff switches transitioned from RUN to CUTOFF position. One of the pilots asks the other why did he cutoff. The other pilot responded that he did not do so. 08:08:52 Engine 1 fuel cutoff switch transitioned from CUTOFF to RUN 08:08:56 Engine 2 fuel cutoff switch also transitions from CUTOFF to RUN Who (or what?) operated the cutoff switches? Does the FDR actually have some input of the physical position of the switches or is it just measuring the output signal voltage which might be changed by a momentary short from liquid or swarf. Both signals go to cutoff within 1 second but then one recovers four seconds after the other. Surely a pilot discovering a turned off switch would have both back on in less than four seconds. 10 users liked this post. Reply to this quoting this original post. You need to be logged in. Not available on closed threads. |
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