Posts about: "Fuel Cutoff Switches" [Posts: 827 Pages: 42]

Honeywell Switch Gate Configurations (Ref: honeywell_hwscs06627_1-1735572)

This extract from the datasheet of the Honeywell switch installed in the B787 for switching between Cut Off and Run shows the various gates that can be incorporated in such a switch. I suspect that it is Configuration D which allows the switch to be in one or other of only 2 positions. But the centre gate has a relatively wide flat table on which the switch can rest if it is not moved correctly to either the Run or Cut Off position. I therefore think that it is not beyond the realm of possibility that both switches may have initially been resting on the gate and then slipped into the cut off position during take off. However, what militates against this theory are the words of the challenge, "Why did you do that?" suggesting that one pilot had seen the other pilot actually flip the switches.

Good question as the report says FAA advisory NM-18-33 (check for potential fuel cut-off switches fault) was not implemented by Air India.

That seems to me to be a very feasible possibility. Noticing, then accidentally hittting the wrong thing in a quick reaction, especially during a possibly bumpy take-off, then only realsing as power starts to die away... A very simple human error possibility - and the switch location makes it horribly easy, especially ofthe switch locking is dubious. Ergonomics and human factors in design? In a very different environment many years ago I was involved in investigating somethimg rather similar (though not deadly). Taught me a lot about operational human factors and our design assumptions...

It's possible, damn it. How dreadful if correct.

That is also a worrying place to put vital switches. Handy place to rest your arm. I have one person I fly with who tends to rest his hand right on the flap lever (light aircraft) if he is not handling the aircraft. I really don't like that. It's bit like my current car, which has the handbrake 'switch'(!) on the central console, behind the gear lever. Just right for accidental operation - and it has been done.

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.

The only people proposing that something jammed or fell on the fuel shutoff switches, causing them to move to cutoff, are those that have never ever come close to physically touching these switches for real. Everyone who operates these switches every day, says it’s almost an impossibly, and that the switches had to be manually moved to cutoff.

Given the fuel shutoff switches were moved back to run, and then subsequently survived the entire crash without moving position, I think the “iPhone/credit card moved them” theory can be put to bed.

Maybe it’s time some of those who lack the knowledge and experience of operating jet aircraft stop and listen to those that do. Even if they don’t like what they hear.

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?

I still think it should be possible to identify the voices from the CVR. During taxi out with P2 as pilot flying the exchanges between them should be obvious as to who is speaking. Thus the identity of the pilot asking about cut off would become clear.

NM-18-33 SAIB left me wondering the same thing. It give a procedure for detecting the defect but omits to explain the cause. I was thinking that the wrong switches had been supplied/fitted. Assuming the image from the Chinese web site is correct, it is disappointing that the actuator can get into that state. I did not see anything that said whether that was how the switch arrived from Honeywell or if there was a defect that allowed the actuator to turn.

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.

SLF. But I've read in full both original threads and this thread.

The Preliminary Report is written in excellent English, so I think one should pay close attention to what it says.

One thing I noticed is that at the bottom of P4 NTSB are stated as "..participated in the investigation". However UK AAIB are only stated as "visited the site". My reading is that UK AAIB are not participating?

Another is that some items on the timescale are v precise, others much more vague.

A question :

If the fuel switches were moved to cutoff, for whatever reason, what exactly would each pilot see as an EICAS warning. I'm still unclear why one pilot asked the other why he cut off - actual observation of the action, or message.

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/

Quote:

"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."

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 ?

3 possibilities come to mind:

1. Pilot who moved fuel switches to off did not do so intentionally to cause the outcome, but for some reason unknown (extreme fatigue, medical condition, medication/drug) somehow confused the action of retracting gear with shutdown procedure at end of flight.

2. Unthinkably, but very possibly, pilot who moved fuel switches did so intentionally, likely planned ahead of time to catch out other pilot at a moment where focus was intently on flying & recovery most unlikely. Mental illness, drug use, personal circumstances behind it.

3. Something extraordinary which was never encountered before which caused or allowed fuel switches to move on their own.

When both pilots flying & personal history is investigated, more is likely to emerge, maybe something to support possibility 1 above, where a pilot had on some previous occasions got sequences confused, or suffered brief episodes of seizures whee he took strange actions.

10 seconds to respond is a long long time if you’ve just made a silly mistake, you’d have those switches back on in a second. The startle factor isn’t really a factor here, because you know what just happened.
What is also unusual to me is the 4 second gap between moving Eng 1 fuel switch from cutoff to run, and moving Eng 2 fuel switch from cutoff to run.

One would imagine that in this situation, speed of response would have been critical. Why the slow, deliberate ‘reaction’?

I believe the fuel cutoff switches are one of the exceptions to this. They are direct wired. Stab trim may well be too.

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.

I think I have seen a previous reference that the generators are disconnected when you select the switches to cutoff (or very shortly afterwards), not when the engine actually drops below idle. That could account for a few seconds of spool down time.

That is a very good question IMHO.

tdracer hit the nail on the head in one of the earlier threads. Two possibilities: Software shut down the engines, or someone put the fuel switches to cutoff.

It wasn\x92t software. The question now is who shut down the engines and why?

Argue fuel switches mechanics, liquid, falling items, electronics, etc, as much as you want, but who and why is where we will end up.

On a British twin fast jet in the early 80\x92s a pilot incorrectly assessed his accel on take off in formation was too slow. In aborting he moved his hand towards the hook deployment lever under the LH console which required a cupped hand, straight pull back to drop the hook. Instead he flipped out a horizontal lever on the side of the same console that he then grasped and pulled back, jettisoning the canopy\x85The aviation psychologist explained that once the wrong handle was selected, even though it required a different method of operation , the brain ( muscle memory) would trigger the correct action to operate it. That would explain the action of operating the incorrect switch.
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.

This crossed my mind too. This is called an "action-slip" by designers: a valid and frequently practised action being applied to entirely the wrong situation, resulting in an (extremely) invalid action.

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.

Unlikely though, I would hope.

Has anyone answered whether there is any message when the engine CutOff switches are transitioned in this situation?

If there isn't then the asker must have seen it being done. If there is, then it's still not absolutely pinned to a pilot, is it?

Just read all 16 pages - been flying! I think comment \x93why did you cutoff\x94 is not the reaction I would expect from a Training Captain who has just witnessed the co-pilot turn both fuel control switches off. They would possibly utter an exclamation, but would surely correct the error immediately - this didn\x92t happen for 10secs. The words are more likely to have come from an FO who has both hands on the control column and is concentrating on the rotation.

Every flight we do as PM we move both fuel control switches to cutoff, 1 after the other, with a gap of about 1 sec between each one. It\x92s a learnt action in response to the phrase \x93shutdown\x94.
Every sim the TC has conducted he will have moved critical switches without much thought in order to setup the sim for the exercise. I remember being slightly shocked one day on the aircraft, having been training in the sim the previous day, that I nearly operated a critical control without thought. It\x92s something I had to consciously guard against after that.

There is no rational explanation for doing it though - moving both fuel control switches down instead of moving the gear lever up is not a likely action slip. It seems either a totally subconscious act or a totally deliberate act.

Engine shutdown/restart.
As Captains of Boeing twins, which fuel switch do you typically move first, Eng 1 or Eng 2?
As First Officers, same question.

Higher probability that the PM (Captain) manipulated the switches given the sequence of events.