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

There are no time stamps on the reported conversation; the comment 'why did you cut off' could have been made after the switches were returned to run position.

It would have been a Christmas tree of EICAS alerts

CVR should have recorded the beeper too, inhibits are for ground only.

Reminder: the prelim report didn't say exactly what the pilots said, and I also think it's unlikely that they said it in English anyway.
So there's no value in wondering what motivated one pilot to say "why did you cutoff" because we don't know if that's what was said.
The exact wording in the report is:
Given the need to couch the report's wording in neutral/diplomatic terms (expletives?), and almost certainly to translate the conversation from another language, the inferences being drawn from those lines in the report are going wildly beyond what is reasonable.

Either the mods have removed the multiple previous posts in the thread that ask precisely this question, or you have some more reading to do...

My take is there is a lot of significant info purposely left out of the preliminary report. For instance, the status of the fuel cutoff switches was not mentioned. Maybe that is the info being sort by “stakeholders” and the “components of interest” that were “quarantined” were the fuel cutoff switches. “Initial leads” is also interesting.

I was just looking into these Honeywell TL family switches for a different project. There are certain part numbers that have the locking mechanism - the ones that don't are clearly different. I didn't see anything to indicate that the locking feature was selectable or defeatable. I suspect the faulty 737 switches fron 2018 had an issue with the detent machining or maybe the loading spring - i.e. a bad batch.

FADEC processes the fuel control switches as well as the throttle resolvers directly. Both dual-channel, separate and separated circuits. Additional logic between the two would have to be foolproof. Sometimes simpler is better, even if human actions can defeat it. There is no plausible explanation or expectation for cutting both switches three seconds after liftoff.

Didn\x92t have to be but every mechanic would have simply wiggled the switch.
The throttle quadrant was also replaced.

Thats twice after the 2018 Boeing Service Bulletin so it\x92s not even applicable anymore.

Takeoff performance assumes a single engine loss - 50% of thrust for a twin - at V1, assuming V1 occurred at the correct time and place on the runway (before that, RTO). It is really an integral or area under the curve issue.

With about 10 seconds between to-Cutoff and back-to-Run, it.is hard to see recovery with any terrain or obstacles present. Perhaps, assuming accidental Cutoff, they were restored within a second or two, the Quick Relight could have restored thrust rapidly as the engines were still spooling down - then it is a matter of the built-in margins in the takeoff performance. But the report said the engines both were sub-idle when the Quick Relight logic would have reactivated with the restoration to Run.

I doubt it was close - up to 10 seconds with 100% thrust loss. It could easily be evaluated in a Simulator, but not sure it matters now.

My recollection is that the fire handle will be locked in this circumstance, unless the respective fuel control switch is at Cutoff. Engine fire procedure (and not before 400 ft AGL) is fuel control switch to Cutoff and then pull the fire handle (turn left for bottle 1, turn right for bottle 2).

But there was electrical power to the switch.

Would not expect an FDR dedicated pole. They might pull the FCS position from the FADEC, since what really matters is what the FADEC receives as a command. I would expect two poles dedicated to the two circuits, one routed to each FADEC channel, and the others to the non-FADEC-reset-command functions.

There is a lock release on the fire handles.

The 1 second is consistent with the fuel control switch sampling rate. I wouldn't read too much into that, it is anywhere from simultaneous to 2 seconds within the sampling rate. (The sampling used to be 1Hz for that discrete). The FADEC will give better information on the exact time that the engines fuel was shut off.

There is one known inadvertent shutdown with this type of switch, on a B744, many years ago, when the Rosen visor fell from the upper sun visor rail when being relocated. That managed to turn off 1 fuel switch.

The report is quite comprehensive for an interim report, and it does not draw any conclusions as yet as to how or why the fuel control discrete is recorded as OFF, however, it is troubling. I would reserve opinion until there is a clear spectral analysis that shows the selection of the fuel switches off, and then back on.

As to the time to react, the crew in this case if unaware of the causation will have a fair recognition time to assimilate the information that is presented, and then to determine that the cause is the switches being off is going to take some time to process, discover the system status and respond, if that is what happened. I remain concerned with liquid ingress to the control system, giving a change in the sensed switch position rather than the selected position. That is looking like a long shot, but then this event is way outside of the normal box.

Basically, the preliminary report has narrowed down the cause of the disaster and discounted a few earlier theories such as flaps up instead of gear up, but there are a lot of questions still to be answered. We need to know; who, how and why.

The switches could have been set to cut off in error even though this was denied on the CVR. However anyone with experience in this part of the world knows that owning up to mistakes isn't a common practice.

I'd rule out a suicide attempt because if the pilot doing it had moved to switches to cut off and the other pilot had put them back on, a hard push forward on the control column at that height would have settled the matter.

I'm not yet convinced that the aircraft isn't responsible due to a technical fault or improper maintenance.

Neither Germanwings 9525 nor MH370 (most likely) were 'quick and dirty' suicides in that sense. People are weird. Cutting the fuel at such a critical stage of the flight is psychologically different than actively flying it into the ground. Think resignation vs assertion. They may have calculated it as unrecoverable anyway. There is also the plausible deniability or at least it may never be known, for sure, which pilot did it. This may offer some protection to the guilty pilot's family because their shame will be far greater than in Western countries.

Sorry, I have to seriously disagree, in the nicest possible way, I hope.

The switches must be accessible - Yes
They are where hands regularly pass over them - a No. As I see it, a certain expression regarding the back end of a male dog comes to mind!
Able to be actioned quickly - arguably, currently, it's much too quickly, IMHO.
Guarded - when it comes to Cerebellum (Yes, please search that word in this thread)-generated actions, that makes zero difference. When the Cerebellum has been trained and learned, it will repeat the most complex sequences you can think of - without you having to think of them. That's the REAL problem that needs to be solved.
Logical - Yes, but really No! Putting them close together can more easily result in the wrong action at times of high stress, confusion, fear, danger, urgency, whatever.

I say they need a major, i.e. Total redesign.

But one of the big problems is that these two switches are used at least a couple of times on every flight. So, they are true Cerebellum Fodder.

However, here's one suggestion. The modern plane is full of sensors, interlocks and logic devices. Use them a bit smarter, I say!

When the plane is on the ground, allow the Fuel Switches to be turned On and Off without debate. But using Air/Ground and /(or?) WoW, when the plane is in the air, the process must be made markedly different. At the very LEAST, make them properly guarded, so a flap must be lifted to action them. And as soon as the flap gets lifted in flight, a very loud alarm and maybe a light is triggered. Then, everybody knows, no need for guessing. Until you or your fellow pilot presses the Confirm button somewhere nearby, the switches can't be moved - or are disabled, or something.

If you don't regularly use this procedure, the Cerebellum won't be so likely to Run It Automatically in a panicked rush. The different process from what you did just at the start of the flight will trip up the cerebellum somewhat, and trigger the Higher Brain to start thinking...: "What? Is this correct?"

How about this?

Subsequent thoughts: The Confirm button would only remain live for a short period, say 3 seconds, during which time, you can operate the switch. Then it resets.
Another idea: Leave the Fuel Cutoff switches right where they are, as they are. But, when in Flight, totally disable them. Alarm if moved. Put the In-Flight Shutoff switches in the overhead panel, with the same kind of aural/visual Confirmation-required warning system permanently operative.

P.P.S. That may not be enough, maybe there needs to be a Takeoff speed transition added - i.e. Before Rotate. Maybe just after V1?

Industrial electrician here.

I have only seen a diagram for I think the 737. I remember there being a listing of what each pole did, but I can no longer find the post.

My expectation/speculation, though, is this:

The EAFR gets its information on cutoff switch position from the FADECs via data buses, similar to almost all other engine data. We have N2 information in the report after the engines were switched off, so clearly there are no concerns about this data not being captured.
This means that the FADEC's data of where the switches are is almost certainly the EAFR's data.

There are other poles on the switches that do other things - I think it was opening/closing the LPSOV and enabling the generators. The fourth pole in the 'cutoff' position was IIRC not used because the generators don't get a disable signal, whereas the LPSOVs are powered open in the run position and powered closed in the cutoff position.

If the switches were physically operated and in good electromechanical condition (not counting the possibly faulty gates), we would expect all four poles to operate essentially simultaneously, with the four 'run' contacts opening and the four 'cutoff' contacts closing. Not only would the EAFR pick up that the FADECs were commanded off, but also that the LPSOV closes after a short delay, and the generators drop offline before N2 drops below idle.

When the switches are moved back to run, we would likewise see the position of each LPSOV return to open.

(this does not necessarily mean that a person intentionally operated them, but that the lever actually moved).

If there was a wiring fault, contamination, or internal switch failure, we would probably not see this. Instead, you might see the LPSOV remain open despite the engine shutting down, or perhaps the FADECs trying to keep the engine running while the LPSOV has closed and shut off fuel, or the two FADEC channels receiving different run/cutoff signals - and all of this would probably happen differently on each engine (if it affected both engines at all). There is no indication of this in the report.

These are not your basic light switch where the load is either powered or not powered. They're four switches ganged together and operated in unison, and each channel powers either thing A or thing B. If you have both or neither A & B powered (for longer than the ~50ms that the switch takes to move between positions), this is a fault that should be visible in the EAFR data in some/many cases. Think valves being displayed in orange as 'position unknown'.

If all run contacts opened, and all cutoff contacts closed, the switch moved from run to cutoff .

I don't know whether they analysed the EAFR data in this much detail yet, but coupled with a potential click sound on the CVR, I think there's going to be very very little doubt at the end of the investigation whether the switches physically moved or not, and I strongly expect they did.

The flight deck of a modern airliner, especially at takeoff, isn't some cluttered artists studio with a one wheeled bicycle behind the seats. There aren't books and straps and whatever all over the controls (or the dashboard - it's SOP not to ever put anything on the dashboard in a lot of airlines). Nothing is going to fall on the switches and nothing is suddenly going to creep under the fire handles, which by the way, have an integrated physical lock and require a double action to activate. Yes of course the fuel switches and fire handles are separate, they are different controls, and do different things.

@Maybeitis, how about we leave the total redesign of the fuel switch locations and operation (which have been moved billions of times in thousands of aircraft without a hitch) until the final report is out.
These were deliberately moved. It wasn't a brain-fart. Unless the interim report omits crew calls which turn the scenario on it's head.