Posts about: "Fuel (All)" [Posts: 1005 Pages: 51]

From the CVR, the switch position was noticed, questioned, and with understanding selected to Run; the crew apparently had a quick understanding of what would be a very surprising situation - startle, mind numbing, thought restricting conditions.

It is reported that P2 was handling; in this case the Captain might guard the thrust levers until V1, moving his hands away, but not onto the control wheel - rearwards, … thence with cuffed sleeve …

A speculative scenario of inadvertent switch operation of 'unguarded' switches.

A combination of most unlikely - unbelievable factors, which came together at that time. Yet such rarities and combinations litter the wreckage of past accidents; and with hindsight they were 'normal'.
Normal SOP for P2 takeoff; errant switches escaped SAID checks - 'normal' for that aircraft.

If the switches were inadvertently moved, the realisation, even subconsciously, might support the apparent quick understanding and action.

… waiting for: a report on the condition of the cutoff switches condition wrt guarded operation …

(1) is true I give you that, but there is no followup "I didn't.. oh crap", denial is a reasonable response if you truly haven't registered doing something, but it is also a reasonable response if you want to confuse to delay

By precedent in routine operations I mean: is there a single example of these switches being cut off at takeoff like this? There is precedent for the wrong engine being shut down in a fire sure, and there is perhaps precedent for mishaps with the fuel switches in other cockpit layouts - but in the case of this layout, with this model of switch or even this 'style' of switch and placement, I cannot find a single example that would come close to the level of catastrophic action slip of pulling out and setting to cutoff both switches one by one.

I think the preliminary report is supposed to present all factual information - they could have left out "why did you cutoff / I did not" - I could understand if they left out sounds that could be ambiguous, perhaps indicating a struggle but not clear enough to present as fact. However, "positive rate / gear up" followed by 2 switches instead of gear handle is completely factual and relevant information, to exclude it makes no sense.

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 no pilot moved the switches, equally 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 is 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.

I have rebuilt the site that organises this thread by subject here: https://paulross.github.io/pprune-th...171/index.html

It studies 3703 posts (and discards 1043 of them).

Changes:

- Add subjects: "Action slip", "AvHerald", "Human Factors", 'Pilot "Why did you cut off"'.
- Build threads up to July 13, 2025, 10:57:00 (built on July 13, 2025, 12:02:17).

Project is here: https://github.com/paulross/pprune-threads
Raise issues here https://github.com/paulross/pprune-threads/issues or PM me.

You could be quite right and I do agree that most action slips are for switches and levers operated in roughly the same phase of flight. Really hard to resolve one way or the other as in both cases of deliberate or subconscious action, it\x92s hard to apply logic to a mind that can be illogical\x85shipiskan\x92s post above being an example.

Almost as though the hand which reached out to raise the gear while the brain was thinking about something else found the fuel cutoff switches and managed to manipulate them to off without the brain ever becoming involved?

Very helpful, thanks! One recommendation for change: since we don't know what words were used by the pilots, how about using "CVR: query cutoff" rather than "why did you cutoff"?
Most of your comments in the thread are extremely sensible but I take issue with both points you made in this post.

Firstly, you'll have seen plenty of things to disprove the "without a hitch" in this thread alone , and as a professional pilot you'll no doubt know of many others - including switches moved in-flight as a brain-fart , or switches moved by things like falling objects. Waiting for the final report may tell us if it would have made a difference in this case, but the lower tier of the safety pyramid (non-severe outcomes) is definitely already populated with plenty of examples of "hitches".

Secondly, I'm absolutely inclined to agree that the switches were moved deliberately (though perhaps absent-mindedly), but I'm genuinely shocked and baffled that you are already willing to assert that "It wasn't a brain-fart". Perhaps those words were typed in haste and you didn't re-read what you had written? (A brain-fart, in other words.)
That interview has a series of very poorly judged comments by someone who should certainly know better, and IMHO adds nothing of value. It doesn't even acknowledge the possibility of an action-slip/brain-fart/execution-error as cause, and the interviewee voices his suspicion about a cover-up based on the identities of the speakers of key remarks not being shared at this point. Surreal.

From the Manuals AMM - IPD - WDM - CMM - Avoiding speculation in this post. Just Facts.

Cutoff Switch

Each switch has 14 pins - 4 sets of contacts

Designation | Cutoff | Common | Run
A | 1 | 2 | 3
B | 4 | 5 | 6
C | 7 | 8 | 9
D | 10 | 11 | 12

Pins 13 and 14 power the LED - Powered by Capt Instrument bus 28vdc - signal from common core sys

A Contacts feed an RDC
B Contacts feed a different RDC
C Leads to Engine Fuel Control Relay 2(L or R)
D Leads to Engine Fuel Control Relay 1(L or R) AND Engine Fuel Relay 1



The common pins are all GND. Positive voltage is suppled to the cutoff and run pins.
The relays - do various things. I cant detail everywhere they lead to.
The AMM States that the manufacturer for the engine fuel control switches has determined that you should not replace the switches on-wing, and that you should replace the thrust control module instead.

Thrust Control Module

This LRU (replaced twice per the interim report) - contains the cutoff switches.
The CMM for the Thrust Control Module does not call out a test of the locking feature that I can find. It does perform various tests of the switch function.

Seems fair, thanks! I rattled it off in 10 minutes so suggestions/error checking welcome

Latest version:

It said within 10 seconds.

Being cynical and suggesting the worst case scenario....

To place the 'blame' on the other pilot, knowing that the audio would be listened to at the subsequent investigation.
I.e. possible scenario...

Pilot A selects the switches to 'cut off'.
Pilot A asks why 'he' (pilot B) did that.
Pilot B (indignantly and truthfully) says 'I did not do that'.
Hence 'listeners' assume that Pilot B selected the switches to 'Cut off' because why would Pilot A ask the question if he did it himself.

That's a worse case scenario of the aircraft being brought down deliberately and one of the pilots trying to place the blame on the other one.
But we cannot know more until the final report is published. And until medical reports are conducted on the pilots.

We can only hope that this scenario is not true and that there is some other reason for this tragic incident.

(SLF / Lawyer) I wrote early in the old thread that realistically only the FCS could be considered, pointing to the bulletin and suggesting that a foreign object might have affected both FCS simultaneously. After everything I've read here, I stick to that. Why? If the F/O was the PF, then only the PM could have operated the FCS. An unconscious action seems unlikely because it would have required not one but two unconscious actions, even if in quick succession. I consider that rather improbable. If it was a conscious action, wouldn\x92t the captain have taken over the flight instead? Unless one argues that the FCS had the lowest threshold and promised the safest outcome in this situation. Pilots could probably assess that better. But: How would it have turned out if the PF had reacted immediately and switched the FCS back on? Would the aircraft have been salvageable? If so, wouldn\x92t the PM have wanted to prevent this scenario and re-deactivated the FCS in Cut off position? In short: I think there are safer methods. Or am I mistaken?

This is excellent, thank you. It has helped me to crystallise a thought about the length of time the switches were at cut off.

10 seconds is a long time in a life threatening situation (like most clich\xe9s, the cinematic trope of time slowing down only reflects people's real experiences, mine included). Reaction times to completely unexpected events can be in the order of 3-5 seconds, but I find it hard to think that it would have taken any pilot as much as 5-7 seconds to set the first switch back to run. It's not something that anyone trying to save the aircraft is going to take time to consider.

Possible explanations for the length of time are a physical altercation - but if that was so, then why did the switches then stay at run? We will be none the wiser on that, at least until the next report. Another, perhaps more likely possibility is that the switch movement itself was unnoticed by at least one of the pilots, and was not noticed until its effects took hold a couple of seconds later (my phrasing here is intended to leave open the question of how the switch moved, or was moved). Combined with the startle reaction time, this would start to explain a 10 second delay. So I expect the CVR comments are towards the later end of the possible range indicated in the excellent diagram.

I'm not sure it is amazing? All I read into the report's words is that the FCSs were turned on, I assume that this will see fuel flow to the combustion chambers and ignitors within 1s, and if the fuel ignites (why not?) EGT rises and the report records this as "relit".
The low airspeed airflow through engine and HP RPM on Eng 1 were sufficient to allow HP RPM to increase. The longer delay between Eng 2 OFF then ON allowed HP RPM to decay more than #1, and although 'relit', I read a successful (unassisted) spool up was unlikely? (i.e. a detailed unassisted relight envelope including current HP RPM and IAS would have #1 in the envelope and #2 outside).

As a wild guess, if he knew it would not succeed (and it true, was correct and recovery was not even close to being possible)

To be frank, we do not know he did not. The report has been (IMHO) carefully sanitised to remove any evidence indicating it was (or not) a suicide attempt, which pilot said what, when they said it, no indication these were the exact words, and no indication that there is not plenty more conversation available.

If we want to speculate in this area, one could ask (my best guess):

1. Do the AAIB know who said "why" and who "I did not"? (Yes)
2. Are they the exact words? (No) Or a 'summary'? (Yes)
3. Were other words spoken by one of both pilots? (Yes)
4. Do the AAIB know whether there were or were not other cockpit occupants? (Yes) Were there? (No - since to fail to mention it casts assertions on just 2 named individuals)
5. Are the AAIB fairly certain of the root cause of this accident (Yes i.e. mechanical issue, unintentional HF, unlawful interference) If yes, have the AAIB deliberately sanitised this report to conceal both the root cause, and other information that would lead to uninformed speculation that does not further flight safety (Yes)

I agree there was a general feeling in threads that whatever happened was highly unusual even in the realm of accidents / Swiss-cheese model, and that deliberate action was unthinkable yet entirely possible. Many elaborate theories were proposed, I myself proposed a precedent for software architecture taking all 4 AC generators offline leading to a struggle for engine driven fuel pumps to deliver - a theory I have now obviously abandoned.

The fact is the moment the report was released all other previous theories were all but invalidated and deliberate action became 2nd or 1st most probable.

• Could a wiring fault / short circuit explain the cutoff without switch movement - someone posted the pinouts above, these are not single-pole switches, the wiring architecture is designed to mitigate such faults. If the switches didn't move but cutoff was acknowledged then they either self-resolved 10s later, or they were then cycled to cutoff and back to run. Improbable but possible, but the report doesn't support this and there is no precedent for it, even for a single switch not resulting in accident
• Could these be the previously mentioned switches without the locking mechanism - even if that were the case, nobody has presented a report in over half a decade that could align precedent with such a failure - where is the report of even 1 of these switches being bumped accidentally, or due to turbulence, or on landing impact? The probability that the first manifestation of these inadequate switches was this particular 1-by-1 sequence 3 seconds after takeoff, after several years, not at any other phase, it seems quite low

I would argue that your version of how it happened is highly speculative though. I agree that the pilot monitoring is the more likely one to do it but its just as likely that the other pilot saw in their periphery, or heard, or otherwise deduced the switch movement and that the pilot who did it denied it - either because they genuinely believed they had not done it (psychological episode or oops), or because they wanted to delay reaction. It's also possible that the other pilot moved them back to run, perhaps with a slight struggle - again I'm speculating as well.

I do agree that at this point deliberate action is the most likely cause, followed by extreme psychological episode. Casual accidental movement if it was remotely probable would surely have been detected in decades of operation and mitigated with a redesign.

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?

The AAIB could have omitted the exchange between the pilots, or said something more neutral like "In response to a question, a crew member stated that he had not cut off the engines." To me, the fact that they chose to paraphrase that particular exchange in the particular way they did speaks volumes.

If the captain did cut, and then when challenged reverse his actions, I doubt he would expedite the procedure.
I'm not implicating either pilot, without more evidence.

When the engines are shut down, where does the power supply to the Fuel Cut Off Switches come from?
If powered by the RAT or APU would that introduce a time delay before you an can effectively put them back to Run?

Because the suspect who put the switches to off was not cooperative, would be my guess.