July 10, 2025, 12:31:00 GMT
permalink Post: 11918989
The switch itself is 4-pole, or a double-on, double-on switch, capable of independentently signaling whrough completely isolated poles. The plot thickens. IF the switches really are involved, there is either some kind of shortcut in within the LRU/very messed up witing harness, some freak automated muscle memory thing or deliberate action.
July 10, 2025, 12:33:00 GMT
permalink Post: 11918993
Worst case, at next idle TLA, engine shuts down. I bet eyes go to cutoff switches after a scan, surely EICAS/ECAM has a Captain Obvious alert set.
Runaway RPM or locked RPM, some FADECS latch at 86 or so % N1- you'd still need TLA of idle for the cut off switch to work.
Volcanic ash, loss of all engines, desire the simultaneous FADEC reset of cycling the cutoffs- just coordinate with PM for idle TLA.
Other jets have this standard, today.
Who flies the throttles in normal? PF
Who typically performs the steps, including idle TLA of shutdown/restart in flight? PM.
Last edited by moosepileit; 10th July 2025 at 12:46 .
July 10, 2025, 13:04:00 GMT
permalink Post: 11919015
AI171 Thread by Subject
I have rebuilt the site that organises this thread by subject here:
https://paulross.github.io/pprune-th...171/index.html
Changes:
Raise issues here https://github.com/paulross/pprune-threads/issues or PM me.
Changes:
- Built the thread up to July 10, 2025, 12:31:00
- Add subjects: Relight, 51 Day Issue, Fuel Cutoff Switches (detent), ICAO, Fuel Cutoff Switches, Memory Items, Annex 13, Simulation Scenarios.
- Various technical fixes should give a better/more accurate presentation.
Raise issues here https://github.com/paulross/pprune-threads/issues or PM me.
July 10, 2025, 13:18:00 GMT
permalink Post: 11919024
The data recorder has all the information most are questioning. They already know if the fuel control switches were selected to cutoff and they know if this happened before or after the loss of thrust. Perhaps the sequence of events will be more clear tomorrow. I can tell you that from aircraft rotation to loss of thrust was a very short time period. Perhaps 8 seconds. I simply won’t believe in that time period the crew were taking any non deliberate actions that would have shut the motors down.
- They know exactly 1 fuel switch was cut off, perhaps implying single engine failure + wrong engine shutdown
- They know 1 or both switches were cycled off then on, implying a last-ditch attempt at some sort reset at any point up to say ~30s
- They know both fuel switches were cut off, and remained off, implying sabotage
- If the cut off happened within 20s of leaving the ground perhaps it could explain why CCTV shows the initial climb then level for ~10s before descent. It could also explain the RAT and gear trucks perhaps if gear up was delayed? However, in this scenario they must know that the engine failed, that information would be clearly recorded and surely the leak would lead with that info? Also 'switches' is plural implying both, the radio call didn't mention single engine failure and like you say its quite hasty, even within 20s.
- Again assuming switches plural, this implies either of the prevailing theories of dual engine failure leading to loss of AC or loss of AC leading to reduced thrust or engine failure. However, it also seems strange to lead with that info rather than the state of the engines or electrical systems in any flight data, unless someone can explain how the data would be impacted?
- If this was the case then it would imply that there is no voice or engine data to explain the cut off, nothing was said and the engines were normal up until that point
July 10, 2025, 13:33:00 GMT
permalink Post: 11919031
Just for emphasis, the fuel control switches control both the spar valve AND the shutoff inside the fuel controller at the engine. It’s not the spar valve the starves the engine of fuel it’s the HP valve. If it were only the spar valve, shut downs at the gate would take awhile.
July 10, 2025, 13:45:00 GMT
permalink Post: 11919035
Just for emphasis, the fuel control switches control both the spar valve AND the shutoff inside the fuel controller at the engine. It\x92s not the spar valve the starves the engine of fuel it\x92s the HP valve. If it were only the spar valve, shut downs at the gate would take awhile.
July 10, 2025, 13:58:00 GMT
permalink Post: 11919040
Just for emphasis, the fuel control switches control both the spar valve AND the shutoff inside the fuel controller at the engine. It\x92s not the spar valve the starves the engine of fuel it\x92s the HP valve. If it were only the spar valve, shut downs at the gate would take awhile.
July 10, 2025, 15:10:00 GMT
permalink Post: 11919084
I'm trying to mix the best of the old and the new.
Fast, erroneous, uncoordinated or nefarious- gives a way to intervene, without changing the standards.
Throttles are no longer mechanical. Keep them forward off idle and the cutoff switch does nothing.
Fire/fail/flameout/stall- PM takes the confirmed bad throttle to idle. Then, if appropriate, fuel cutoff and then continue with the fire switch that should also isolate fuel before the engine, air, hydraulics, and electrics.
Bias- I've had mechanical fuel cutoff, mechanical throttles and mechanical isolations- DC9.
Electric throttles, fuel cutoffs and mechanical isolations- C-17s and MD-11s.
Have not had all electrical on switches, throttles and electrical circuits for isolation, only- which allows for more options and unintended consequences.
Last edited by moosepileit; 10th July 2025 at 15:24 .
July 10, 2025, 15:53:00 GMT
permalink Post: 11919101
That does not mean that the pilots "out of habit" would have reverted to the procedure. Who would not? But in that case, the fuel control switches would be found in the RUN position post crash (if anything was left). So did they find the switches in the cutoff position, or did the action of switching got "stored" somewhere in FDM (not a specialist on these things, only to hear many times in the past that "maintenance is already aware" if we had an issue and called maintenance post flight)
July 10, 2025, 15:55:00 GMT
permalink Post: 11919105
That functional separation exists on MD-11 (for which I see you are rated) but not for 777 and 787. The key difference is that MD-11 fire shut off valves (equivalent to Boeing spar valves) are mechanically operated but 777 and 787 spar valves are electrically operated.
Boeing chose to have both the HP and spar valves controlled by the fire handles AND the cut off switches.
July 10, 2025, 16:08:00 GMT
permalink Post: 11919112
With the recent (albeit unofficial) indications that both engine fuel control switches were found in the CUTOFF position, I wonder if it's time to reassess the tone and meaning of Captain Sabharwal's final transmission (perhaps translated from Hindi) “Thrust not achieved… falling… Mayday! Mayday! Mayday!”
Viewed in light of the reported switch positions, the phrasing feels increasingly ambiguous. As is often stated on PPRunE, communication comes after aviation so you wonder why in the crisis and at low altitude, this message was transmitted. Being so atypical, the message merits re-examination.
Viewed in light of the reported switch positions, the phrasing feels increasingly ambiguous. As is often stated on PPRunE, communication comes after aviation so you wonder why in the crisis and at low altitude, this message was transmitted. Being so atypical, the message merits re-examination.
July 10, 2025, 16:26:00 GMT
permalink Post: 11919126
Throttles are no longer mechanical. Keep them forward off idle and the cutoff switch does nothing.
July 10, 2025, 16:30:00 GMT
permalink Post: 11919130
With the recent (albeit unofficial)
indications that both engine fuel control switches were found in the CUTOFF position
, I wonder if it's time to reassess the tone and meaning of Captain Sabharwal's final transmission (perhaps translated from Hindi) \x93Thrust not achieved\x85 falling\x85 Mayday! Mayday! Mayday!\x94
Viewed in light of the reported switch positions, the phrasing feels increasingly ambiguous. As is often stated on PPRunE, communication comes after aviation so you wonder why in the crisis and at low altitude, this message was transmitted. Being so atypical, the message merits re-examination.
Viewed in light of the reported switch positions, the phrasing feels increasingly ambiguous. As is often stated on PPRunE, communication comes after aviation so you wonder why in the crisis and at low altitude, this message was transmitted. Being so atypical, the message merits re-examination.
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?
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
- There is no thrust lever interlock to the fuel control switch function. Don't know of any Boeing design that has that, nor Airbus, but the comment on the MD11 may or may not be valid. MDD had some odd functions in different systems, some good, some, less so.
- Switching off the fuel control switches gives an immediate shutdown, at any time.
- The rumour seems to be quite bizarre, as it presumes that as the aircraft is being rotated, (it still has symmetric thrust at that point) presumably someone with extra sets of hands turns off both fuel control switches, simultaneously. That is a 2 handed action. We are to assume that someone leans over and grabs both switches without the knowledge of the pilot who has at a minimum one hand but procedurally two hands on the control column?
I am no longer interested in being a witness to the abuse of anonymity that arises on this thread.
cheers
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.
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.
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.
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.
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.
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
- 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
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”.
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 .