Posts about: "Fuel Cutoff" [Posts: 302 Pages: 16]

Really? It suggests to me and I would imagine the vast majority of us who have flown modern Boeings that they were physically moved, by one of the crew, one at a time, the question is why.

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.

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.

Probably not during Takeoff I wouldn\x92t have thought.

I cannot imagine a situation where any pilot would be moving a crew bag within seconds of getting airborne.

Was the RAT deployed manually?
The report says, 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?

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.

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.

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?

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: 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 ?

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.

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.

Seriously??
Come on! The gear never moved! You're an Airbus pilot; do you really think that could happen? If so, would the captain then sit there fat, dumb and happy wondering what was now going on... for 10 seconds? Even I would say "Sh1t" and whip those fuel switches back on quicker than the FO could say "WTF!".

Mods, if you don't lock the thread, I'm going back to Facebook!

Loss of hydraulics or electrics will auto deploy the rat. The timing to me however seems to match up with when the engines were selected off.

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

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.

The one pilot asked the other one, \x93why did you cutoff?\x94
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.

Nothing should be ruled out!