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

tdracer
June 17, 2025, 21:41:00 GMT
permalink
Post: 11904694
Originally Posted by Lord Bracken
I was referring to CVR/FDRs in general being specialist equipment requiring specialist facilities to process. In any case, I would be very interested to find out where those from this accident are read. It appears from a post upthread there are new facilities in New Dehli that could be used. Having said that, for the EK 521 accident in Dubai the recorders were sent to the UK for analysis, despite a "flight data recorder centre" in Abu Dhabi being opened (again with much fanfare) by the UAE GCAA five years before the occurrence.
Given the number of times I reviewed DFDR data supplied by an operator after some sort of event/incident, I think most major operators have access to the equipment needed to download a healthy data recorder. So I'd be a bit surprised if Air India does not have this capability. OldnGrounded has also posted that the Indian AAIB also has that ability.

Usually when I hear of data recorders going back to the US NTSB or the recorder manufacturer, it's because the crash damage is such that specialized equipment is needed to download the data. The recorder in the tail would likely have little damage.
While the AAIB may have held off on downloading the recorders until all the major players are present, it's been several days - I'd expect everyone who matters is already there. So I think it is reasonable to believe that the investigators have done a download and have had at least a preliminary look at the data. If there is a smoking gun, they probably already know (and the longer we don't hear something regarding the rest of the 787 fleet, or at least the GEnx powered fleet, the less likely it is that they suspect a systemic problem with the aircraft and/or engine). However the proviso that I posted earlier about potential data loss/corruption due to a sudden shutdown still applies - so maybe the data simply isn't on the recorder.

As has already been posted, EMI is highly unlikely - the current cert requirements for HIRF are quite high, and due to the composite airframe construction of the 787, the lighting requirements are much higher than for conventional aluminum aircraft (the higher resistance of the composite airframe results is higher lightning induced currents).

FDR has suggested a large slug of water hitting critical aircraft electronics at rotation - it is possible that resultant electrical short circuits could falsely signal the engines that the switches are in cutoff. Highly unlikely that it would do that to both engines, but possible.
Then again, all the other plausible explanations are highly unlikely, so...

BTW, I do have a life outside PPRuNe - and I'm going to be traveling the next several days, with limited to non-existent internet access. So don't be surprised if I'm not responding posts or PMs.

The thread is closed so there are no user likes are available.

Squawk7700
June 17, 2025, 23:26:00 GMT
permalink
Post: 11904762
Originally Posted by Lead Balloon
I was struck by a comment in this or the earlier thread that I cannot now find. It was to the effect \x96 I\x92m paraphrasing \x96 that fuel shut off results in an almost immediate cessation of thrust.
Spot on, there's so much fuel being sucked at that power setting, it would be super quick and presumably at near enough to the exact same time.

I assume (rightly so) that you're focused on what could cause them to fail at what appears to be the exact same time given the absence of yaw and any correcting rudder input.

One the face of it, it could only be throttle or fuel supply, with fuel supply only being able to be cut off by valves so abruptly. Any kind of blockage or similar wouldn't give such a result, even if there was a low fuel condition, short of the pickups being exactly right next to each other, presumably that wouldn't give the outcome we've seen.


The thread is closed so there are no user likes are available.

Chiefttp
June 18, 2025, 00:09:00 GMT
permalink
Post: 11904785
Originally Posted by Sailvi767
I agree with what you posted however the solution is so simple that I can’t believe a professional flight crew would not handle it without much of a blip. Push the trust levers forward.
Salvi, just spitballing here, a low alt capture is simple to rectify, but if you’re not expecting it ( perhaps a wrong MCP alt setting) coupled with a HUD , which focuses your attention on it, not the thrust levers, and add to the mix an inexperienced F/O. I can
also see in the final moments of desperation, reaching down and turning the Fuel Control Switches, OFF-THEN-ON, in the hope that an engine will come to life, if they believed that the engine was dead. This may be the reason the RAT extended? Just thinking out loud.

The thread is closed so there are no user likes are available.

Someone Somewhere
June 18, 2025, 13:08:00 GMT
permalink
Post: 11905228
I (and I think everyone else here) have been assuming that the FADEC does in fact have a dedicated permanent-magnet alternator, as is the case on the Airbuses (confirmed by FCOM) and surely the 737.

I have been told elsewhere that this is not the case. A read of the draft FCOM available online for the 777 & 787 makes no mention of a FADEC generator, but then neither does the 737 manuals. Is this simply a case of "Boeing thinks you don't need to know"?

It has been proposed that the primary source of power for the FADECs is actually the flight control PMGs, mounted on the engine gearbox, but that this power goes to the avionics bay, has failover switching gear, and comes back to the EEC.

Can anyone shed concrete light on this (e.g. a source that clearly states there is both an EEC alternator and a flight control PMG on the accessory gearbox)?

Alternator and generator seem to be used interchangeably in this context.

Originally Posted by Lead Balloon
Could someone post an authoritative list of the inputs to the EAFR’s?

By “authoritative”, I mean the actual wiring diagram excerpt of the aircraft model and engine configuration (and hopefully mod state...), that labels each input.
[snip]
It's not quite that, but there is a list of received channels for a GEnx 787 in the FDR report into one of the original battery fires . Unfortunately, it is only a list of parameters that they used and verified in the investigation - the only ones listed for the engines are N1 and cutoff switch. Other accident/incident FDR reports might be more focused on engines and include a similar table.

I don't think you'll find an actual wire list for it (or it won't be useful) as apparently most/all of the data is via an ARINC bus.

I attempted to PM this but your inbox is full.

[SLF with an electrical background and some exposure to ground-side critical facilities power]

Last edited by Someone Somewhere; 18th June 2025 at 13:32 .

The thread is closed so there are no user likes are available.

Gino230
June 18, 2025, 18:38:00 GMT
permalink
Post: 11905461
Originally Posted by N8477G
This isn’t the first one either. On February 9, 2024 a Challenger 600 manuevering to final at Naples FL, (APF) lost both engines simultaneously and crashed on a highway short of the runway. The NTSB final report isn’t out yet so we don’t know that cause either, but the situation was the same. SOMEhow, a highly experienced crew found themselves in a situation from which there was apparently no escape. Whatever the cause was, how did it go un-detected until it produced an accident? (It’s NTSB accident number ERA24FA110. You can find that thread on PPRUNE by searching on Challenger 600. The preliminary NTSB report contains interesting readouts from the FDR. Yes, they lost both fans simultaneously.) I’m not suggesting these two accidents have related causes, I’m only observing that both crews apparently had no way out.


My condolences to all who were lost. Please keep in mind that except by the grace of God it could have been any one of us on that terrible day.

NASA retired, licensed since 1971.
I didn't read that thread, but having flown the aircraft (challenger 600 type), I believe the consensus is that the Captain reaching underneath the thrust levers to actuate the flaps can (and has) resulted in the "triggers" on the back of the thrust levers being engaged- if this is done while the FO is bringing the thrust to idle, it can result in going below the idle stop to cutoff. In other words, the engines were inadvertently shut down.

But I agree that the complete, simultaneous loss of thrust on both engines has to be an astronomical probability, and the cause is going to be interesting to say the least.

I also agree that any one of us could be put in a horrible position within seconds that would be very hard to recover from- the older I get and the more hours I spend in the air, this starts to spend more time in one's consciousness, unfortunately.

BTW calling the crew " highly experienced" is a bit of a stretch IMO, the Captain certainly was, but 1100 hours isn't even enough for an ATP in most countries. For all we know it was not a factor, of course.

PS, what is an SLF??

The thread is closed so there are no user likes are available.

EDLB
June 18, 2025, 19:15:00 GMT
permalink
Post: 11905486
@syseng68k
Consensus here is, that both engines where stopped by a closing fuel cut off valve, wich yields a fast loss of N2. The generators then shut down very quick as does the thrust in a few seconds. This is supported by the quick RAT extension which allowed the crew to control the flight. The APU did autostart too. A thrust changed with the thrust leaver to idle is much slower and would not result in the dramatic change in performance. Thrust set to idle will not engage the RAT since the electric generators would still work. So a thrust leaver changed to idle or any intervention by Autothrust (AT) would not yield to the RAT extension. Something or someone activated a fuel cut off. How and why that happened is the big question, the investigators have to answer.

The thread is closed so there are no user likes are available.

Nick H.
June 18, 2025, 21:30:00 GMT
permalink
Post: 11905563
Originally Posted by EDLB
@syseng68k
Consensus here is, that both engines where stopped by a closing fuel cut off valve, wich yields a fast loss of N2. The generators then shut down very quick as does the thrust in a few seconds. This is supported by the quick RAT extension which allowed the crew to control the flight. The APU did autostart too. A thrust changed with the thrust leaver to idle is much slower and would not result in the dramatic change in performance. Thrust set to idle will not engage the RAT since the electric generators would still work. So a thrust leaver changed to idle or any intervention by Autothrust (AT) would not yield to the RAT extension. Something or someone activated a fuel cut off. How and why that happened is the big question, the investigators have to answer.
A naive glider pilot question: if fuel cut off was (inconceivably) selected, would both fuel control levers have been flipped downwards from Run to Cutoff? And if they were then immediately flipped back to the Run position, how much time would have been needed to achieve enough thrust to maintain altitude?


The thread is closed so there are no user likes are available.

Surlybonds
June 18, 2025, 21:47:00 GMT
permalink
Post: 11905569
The fuel cutoff switches can't be "flipped" in either direction; they have to be lifted over a detent and then moved, a very positive action.

The thread is closed so there are no user likes are available.

777ret
June 18, 2025, 22:38:00 GMT
permalink
Post: 11905597
Originally Posted by EDLB
@syseng68k
Consensus here is, that both engines where stopped by a closing fuel cut off valve, wich yields a fast loss of N2. The generators then shut down very quick as does the thrust in a few seconds. This is supported by the quick RAT extension which allowed the crew to control the flight. The APU did autostart too. A thrust changed with the thrust leaver to idle is much slower and would not result in the dramatic change in performance. Thrust set to idle will not engage the RAT since the electric generators would still work. So a thrust leaver changed to idle or any intervention by Autothrust (AT) would not yield to the RAT extension. Something or someone activated a fuel cut off. How and why that happened is the big question, the investigators have to answer.
The simplest answer: Lo Lvl Alt Cap; Thrust to Idle; Startle Factor; Inappropriate Memory Items : ( RAT deployed; insufficient time for Eng relight.

The thread is closed so there are no user likes are available.

sycamore
June 18, 2025, 22:49:00 GMT
permalink
Post: 11905602
As an ex-tp, I would consider those cut-off switches a danger, and they should have guards either side of each.
Shirtsleeves/watches etc. can get caught, lift switch.
Very poor design. Would not pass `military-muster.`

Last edited by T28B; 18th June 2025 at 23:12 . Reason: Fixed your punctuation.

The thread is closed so there are no user likes are available.

OldnGrounded
June 18, 2025, 23:16:00 GMT
permalink
Post: 11905612
Originally Posted by sycamore
As an ex-tp, I would consider those cut-off switches a danger, and they should have guards either side of each.
Shirtsleeves/watches etc. can get caught, lift switch.
Very poor design. Would not pass `military-muster.`
They're guarded by the switch design/operation itself. To move one of them, the toggle handle has to first be pulled outward.

The thread is closed so there are no user likes are available.

bbofh
June 19, 2025, 01:30:00 GMT
permalink
Post: 11905658
The 787-8 landing gear retraction is primarily hydraulic, using the center hydraulic system for the main operation. However, the alternate gear extension system utilizes a dedicated electric pump to pressurize fluid from the center hydraulic system for gear extension. Obviously due its size and weight and staged retraction, the effort required to raise and stow the gear greatly exceeds that required for extension.

The main gear retraction/extension is controlled by the center hydraulic system.

It is apparent that the hydraulics failed when the engines shut down after breaking the down-locks and leaving the Main Landing gear bogeys in the tilt position, ready for a next step internal stowage and door closure (that was now never to happen). It is therefore apparent that the dual engine failure and consequent automated RAT extension was precipitated by this gear selection or retraction cycle and thus likely to be either WoW micro-switch or 5G Radar altimeter-effect associated. Due to accumulator depletion, the electric pump load would have spiked to replenish it. This may have precipitated the dual engine shutdown due to an unfiltered electrical surge affecting the Ground/Air microswitches (or a local 5G transmission affecting the RADALT) and resetting the TCMA.

The RADALT? Another plausibility? Because of the furore over a spasticated frequency allocation by the US FCC, the US FAA had finally “bought in” and declared that individual nations and their airline operators were responsible for their own 5G frequency spectrum allocations and for taking essential steps to ensure mitigation of the interference effects upon aircraft automated landings and other critical systems caused by their own national approved 5G spectrum decisions. It was admittedly a situation calling for extensive modifications to (and shielding for) the three radar altimeters fitted for redundancy considerations to all modern airliners... for Category 3 ILS approach and landing in zero/zero visibility conditions. The RADALT also features in many air-ground sensing applications. (eg the 747-8).

This was an unusual FAA “passing of the buck” to manufacturers such as Honeywell etc. (to sort out with client operators). But then again, it was not the US FCC’s right to dictate the specific 5G frequencies internationally. These spectrum allocations now vary over the wide selection of 5G phones available (and also nationally). 5G Radar Altimeters constitute a part of the ground/Air sensing that changes the TCMA from ground mode (able to fuel-chop engines) to the air mode (inhibited from doing so)... Ground activation is acceptable ...where fuel chopping of uncommanded thrust can prevent runway sideways excursions or runway length overruns. The question now becomes: “Is it more (or less) safe having an automated fuel-chopping capability on BOTH your left and right, rather than leaving it to the pilot to react via his center console fuel cut-off switches... in the unlikely event of a runaway engine after landing (or during an abandoned take-off)?

5G Frequency Variations

The frequencies of 5G phones vary nationally based on the frequency bands allocated and used by different carriers in each country. In the United States, for example, carriers such as AT&T, Verizon, T-Mobile, and others use a combination of low-band, mid-band, and high-band 5G frequencies. Low-band 5G frequencies typically range from 600 MHz to 1 GHz, mid-band 5G frequencies range from 1.7 GHz to 2.5 GHz, and high-band 5G (mmWave) frequencies start at 24 GHz and go up to 40 GHz . These frequencies are allocated by regulatory bodies such as the Federal Communications Commission (FCC) and can vary between countries based on spectrum availability and regulatory decisions. In other countries, the specific frequency bands used for 5G may differ, leading to variations in the frequencies supported by 5G phones. Additionally, the deployment of 5G networks can also influence the frequencies used, with some countries focusing more on sub-6 GHz bands while others prioritize mmWave technology.

5G interference? It may be an avenue worth exploring?






The thread is closed so there are no user likes are available.

Capn Bloggs
June 19, 2025, 01:40:00 GMT
permalink
Post: 11905665
Originally Posted by Sycamore
As an ex-tp, I would consider those cut-off switches a danger, and they should have guards either side of each.
Shirtsleeves/watches etc. can get caught, lift switch.
Very poor design. Would not pass `military-muster.`
Agree. The two most important controls in the aeroplane, sitting there in a wide-open, unprotected space. After an incident where a manual fell off the coaming (can't remember if a switch got bashed into the Off position), we put guards on our non-787 fuel switches:
Ours:

787:


The thread is closed so there are no user likes are available.

Capn Bloggs
June 19, 2025, 10:22:00 GMT
permalink
Post: 11905892
Originally Posted by DTA
That failure can be the result of physical damage or wear so that the knob is stuck in the pulled position. It would not be obvious if you did not look closely.
Yes, and probably much to @Roo's disgust, we had an instance where an engine shut down all by itself in the cruise; it was concluded that the fuel switch hadn't been "locked" in the ON position and was just sitting on the edge. It was then highlighted to all of us that the FCOM stated "give it a good jiggle" to make doubly sure it was locked in ON.

The thread is closed so there are no user likes are available.

Kraftstoffvondesibel
June 19, 2025, 12:16:00 GMT
permalink
Post: 11905976
Originally Posted by DTA
They comply with a military standard that requires 40,000 cycles though the locking part is tested 20,000 times by just pulling to its full extent. Or something like that. How well that testing matches real world use is debatable.
The spec sheet says 100,000 cycles.
Switches fail sometimes. I have changed lots of lots of malfunctioning toggle switches in my day.
But both at the same time?
It has to be a common thing happening at the same time.
Someone slipping both switches into a worn middle detent is such a thing though, that is one habit that could be developed. A slight bump at takeoff and they both go to cutoff.
Or they are worn and theres an iphone behind the throttles, as someone mentioned.

The switches themselves are on-on 4 pole toggles, and doesn\x92t fail into one position over the other, and gravity would prefer the cutoff position in this design.

I mentioned I have used my share of switches, knobs and buttons. In much larger quantities than what you find in aircraft, but without the life and death factor, and thus no SOP.

Unexpected things happen, no one dies, but I myself brodcasted jolly sounding very inappropriate intro music over a very dark news report on the unravelling Joseph Frietzl case by dropping my phone on a switch. Several million viewers, a good chunk of which called to complain.

Grave errors can be banal.

Other than that, common connectors, the harness itself, I have seen a large amount of unexpected electronic things happen when those get bendt the wrong way.

Last edited by Kraftstoffvondesibel; 19th June 2025 at 12:30 .

The thread is closed so there are no user likes are available.

Seamless
June 19, 2025, 12:27:00 GMT
permalink
Post: 11905984
Originally Posted by Kraftstoffvondesibel
The spec sheet says 100,000 cycles.
Switches fail sometimes. I have changed lots of lots of malfunctioning toggle switches in my day.
But both at the same time?
It has to be a common thing happening at the same time.
Someone slipping both switches into a worn middle detent is such a thing though, that is one habit that could be developed. A slight bump at takeoff and they both go to cutoff.
The switches themselves are on-on 4 pole toggles, and doesn\x92t fail into one position over the other, and gravity would prefer the cutoff position in this design.
This isn\xb4t quite right. They could both have had a malfunction without this being an issue until something or someone hit them at the same time (e.g. on rotation). It\xb4s just another theory which isn\xb4t less plausible than many others.

The thread is closed so there are no user likes are available.

Capn Bloggs
June 19, 2025, 12:29:00 GMT
permalink
Post: 11905985
Originally Posted by syseng68k
Have a few of that type here
That is not a Boeing Fuel switch.

The thread is closed so there are no user likes are available.

Gary Brown
June 19, 2025, 12:49:00 GMT
permalink
Post: 11905995
Originally Posted by Kraftstoffvondesibel
The spec sheet says 100,000 cycles.
Switches fail sometimes. I have changed lots of lots of malfunctioning toggle switches in my day.
But both at the same time?
It has to be a common thing happening at the same time.
Someone slipping both switches into a worn middle detent is such a thing though, that is one habit that could be developed. A slight bump at takeoff and they both go to cutoff. [emphasis added]
Or they are worn and theres an iphone behind the throttles, as someone mentioned.

The switches themselves are on-on 4 pole toggles, and doesn\x92t fail into one position over the other, and gravity would prefer the cutoff position in this design.

I mentioned I have used my share of switches, knobs and buttons. In much larger quantities than what you find in aircraft, but without the life and death factor, and thus no SOP.

Unexpected things happen, no one dies, but I myself brodcasted jolly sounding very inappropriate intro music over a very dark news report on the unravelling Joseph Frietzl case by dropping my phone on a switch. Several million viewers, a good chunk of which called to complain.

Grave errors can be banal.

Other than that, common connectors, the harness itself, I have seen a large amount of unexpected electronic things happen when those get bendt the wrong way.
The extended spec sheet for these switches shows that there are versions with a center indent, and others without. But the picture up above which is said to be of the 787/8 actual switch seems - to me - to not have a center indent option. Ie, it is either on or off, with a spring loaded lift of about 2mm needed to move it from one position to another.

The thread is closed so there are no user likes are available.

Capn Bloggs
June 19, 2025, 12:55:00 GMT
permalink
Post: 11906000
Originally Posted by syseng68K
I guess it depends on the model
Obviously. If yours is the switch I think it is (with the metal, unscrewable dome) then yes, it is very different. Very hard to "balance" yours in the middle.
Not so the Boeing fuel switches: they can be relatively easily "sat" in the middle, on the centre raised bit and could be bumped either way. Hence our (non-787) FCOM saying make sure you jiggle them when you put it in the On position to confirm it's locked there.

The thread is closed so there are no user likes are available.

Xeptu
June 19, 2025, 12:57:00 GMT
permalink
Post: 11906003
Originally Posted by Capn Bloggs
That is not a Boeing Fuel switch.
That's a Beechcraft Kingair starter switch

The thread is closed so there are no user likes are available.