Posts about: "Fuel (All)" [Posts: 345 Pages: 18]

BugBear
2025-06-14T22:24:00
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Post: 11901903
Originally Posted by njc
OK, but even if we do assume that there was a major electrical fault which brought down the main supplies: multiple posts in this thread have already asserted that this would not cause the shutdown of the engines, and that even if the fuel pumps failed, suction would keep the engines running.
If #2 failed and #1 got pulled, how bout dat ? t's pretty clear the crew knew #2 was struggling
FlightDetent
2025-06-14T22:26:00
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Post: 11901906
I am curious to learn what power source drives the high-pressure fuel pumps in the engine. If there is such a thing, I suppose there would.

Gearbox? This is at odds with a possible cascading electric failure that (might have) caused a loss of engine fuel feed.

To my understanding on my ancient plane and engine design, the HP pumps that feed the nozzles are driven mechanically, which enables gravity feeding among other scenarios, but also assures the fuel supply is independent of whatever happens upstream of the nacelle. Except for LP/fire shut-off cocks.
Ornis
2025-06-14T22:33:00
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Post: 11901909
Originally Posted by njc
... multiple posts in this thread have already asserted that this would not cause the shutdown of the engines, and that even if the fuel pumps failed, suction would keep the engines running.
Given it was close to the ground at the time of failure, is it possible a problem raising the gear could allow automation to cut fuel to both engines? (According to this thread, TCMA uses weight on wheels and radar to decide if aircraft is airborne.)
framer
2025-06-14T22:34:00
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Post: 11901910
Now, if I assume the speculation that the RAT deployed is correct, I keep coming up with two potential scenarios that could explain what's known regarding this accident:
1) TCMA activation shutdown the engines
or
2) The fuel cutoff switches were activated.
I literally can come up with no other plausible scenarios.
I\x92d like to give you another option to consider in what must be a worrying time;
Am I right in saying, from a mathmatical perspective, that dual engine flame out due biocide overdose would be more likely than a TCMA activation shutting down the engines? Considering we have examples of engines reducing to idle within seconds of each other in the past, but we have no examples of airborne TCMA issues I would have thought this to be the case. Likewise, nefarious intent also appears more likely statistically than a TCMA issue.
I have high-school level statistics under my belt so I pose that as a question for people much smarter than myself.
mechpowi
2025-06-14T22:39:00
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Post: 11901913
Almost all catastrophic accidents that are not deliberately initiated require multiple causes. It’s extremely unlikely that both engine condition switches or fire switches were accidentaly actuated during a routine rotation and initial climb. However it’s stil possible that the crew did actuate those switches (intentionally or unintentionally) in response to some anomaly experienced at that time. Thus it’s not impossible that electrical system malfunction was the first link in a sequence that led to removing the fuel supply to both engines. The most obvious one is that crew thought that they had dual engine failure due to lost of main electrical power and initiated a double engine restart bycling the engine condition levers.

The purpose of this post is not to promote the above as a possible cause of the accident, but to remaind people that a (proven) mechanical fault does not rule out pilot error and vice versa.
fdr
2025-06-14T23:04:00
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Post: 11901940
Originally Posted by BugBear
If #2 failed and #1 got pulled, how bout dat ? t's pretty clear the crew knew #2 was struggling
If you are referring to loss of all boost pumps, am not aware of any engine that will not continue to run with a suction feed to the main boost pumps at low altitudes. At high altitudes, there is a chance of cavitation of the main pumps but only at very high powers, and generally not at sea level.

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tdracer
2025-06-14T23:05:00
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Post: 11901941
Originally Posted by FlightDetent
I am curious to learn what power source drives the high-pressure fuel pumps in the engine. If there is such a thing, I suppose there would.

Gearbox? This is at odds with a possible cascading electric failure that (might have) caused a loss of engine fuel feed.

To my understanding on my ancient plane and engine design, the HP pumps that feed the nozzles are driven mechanically, which enables gravity feeding among other scenarios, but also assures the fuel supply is independent of whatever happens upstream of the nacelle. Except for LP/fire shut-off cocks.
The engine driven fuel pump is literally driven off the engine gearbox (driven by a mechanical connection to the N2 shaft) - if the engine's running, the gearbox is turning (baring a major mechanical fault). The engine driven fuel pump is a two-stage pump - a centrifugal pump that draws the fuel into the pump (i.e. 'suction feed'), and a gear pump which provides the high-pressure fuel to the engine and as muscle pressure to drive things like the Stator Vane and Bleed Valve actuators. It takes a minimum of ~300 PSI to run the engine - the HPSOV is spring loaded closed and it takes approximately 300 psi to overcome that spring.
Engine driven fuel pump failures are very rare, but have happened (usually with some 'precursor' symptoms that were ignored or mis-diagnosed by maintenance). It would be unheard of for engine driven fuel pumps to fail on both engines on the same flight.

As I've repeatedly posted, even a 100% aircraft power failure would not explain both engines quitting, at least without several other existing faults. Again, never say never, but you can only combine so many 10-9 events before it becomes ridiculous...

TCMA doesn't know what V1 is - it's active whenever the air/ground logic says the aircraft is on-ground.

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fdr
2025-06-14T23:20:00
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Post: 11901949
Originally Posted by tdracer

... The TCMA logic is designed and scrubbed so as to be quite robust - flight test data of the engine response to throttle slams is reviewed to insure there is adequate margin between the TCMA limits and the actual engine responses to prevent improper TCMA activation. Again, never say never, but a whole lot would have had to go wrong in the TCMA logic for it to have activated on this flight.

Now, if I assume the speculation that the RAT deployed is correct, I keep coming up with two potential scenarios that could explain what's known regarding this accident:
1) TCMA activation shutdown the engines
or
2) The fuel cutoff switches were activated.
I literally can come up with no other plausible scenarios.

In all due respect to all the pilots on this forum, I really hope it wasn't TCMA. It wouldn't be the first time a mandated 'safety system' has caused an accident (it wouldn't just be Boeing and GE - TCMA was forced by the FAA and EASA to prevent a scenario that had never caused a fatal accident) ...
TD, in this case, the RT call suggests we are a grand total of 1 choice, and that goes to a fair likelihood that a fleet wide grounding is in the offing. Adding system complexity dependent on sensor reliability has bitten us all in the past and will do again, and I have a bad feeling that is where we are at with this. The SSA guys will be working overtime, but this has had the hall marks of being a bad sensor/system event from the outset. Am laying bets that there will be a fleet wide grounding in the next 3-4 days, if not sooner. Inadvertent GA thrust after landing has occurred before, (had it on a B744 myself), and it is curious but straightforward to handle.

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ams6110
2025-06-14T23:30:00
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Post: 11901954
Originally Posted by fdr
If you are referring to loss of all boost pumps, am not aware of any engine that will not continue to run with a suction feed to the main boost pumps at low altitudes. At high altitudes, there is a chance of cavitation of the main pumps but only at very high powers, and generally not at sea level.
Would the suction feed work if the fuel filters were clogged due to contaminated fuel? Boost pumps will bypass clogged filters but what about suction pumps?

Speculating on a combined loss of electric power plus bad fuel, but seems as likely as any of the other farfetched scenarios.
BugBear
2025-06-14T23:40:00
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Post: 11901962
Howdy

Originally Posted by FlightDetent
I am curious to learn what power source drives the high-pressure fuel pumps in the engine. If there is such a thing, I suppose there would.

Gearbox? This is at odds with a possible cascading electric failure that (might have) caused a loss of engine fuel feed.

To my understanding on my ancient plane and engine design, the HP pumps that feed the nozzles are driven mechanically, which enables gravity feeding among other scenarios, but also assures the fuel supply is independent of whatever happens upstream of the nacelle. Except for LP/fire shut-off cocks.
Originally Posted by benjyyy
There have been conflicting reports about the call to ATC. Original reports quoted the Captain saying "Mayday...no thrust, losing power, cannot lift". But I've seen reports today stating the call was simply "Mayday, Mayday" and then no further response.

Difficult to confirm so I wouldn't put too much weight behind it until something more official is released.
It would also depend on how much is allowed? Surely the investigators will be allowed to hear it? No? Would think it a prerequisite to a full understanding of the flight
BugBear
2025-06-15T00:08:00
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Post: 11901978
Lull

Consider losing one engine on the Dream. If it is a generator that's failed let's say #2 . Do the electric fuel pumps lose power? Only in #2? Does the mechanical pump start feeding right away? If so, is there a lull? Are both engines fuel pumps supplied off one Gen?

See I think there was no simultaneous loss of both 1, 2.
The odds give me a migraine. I still wonder if TCMA knows the difference between parked, rolling, rotated brakes and stowed. Only parenthetically, it didn't do this
MaybeItIs
2025-06-15T00:54:00
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Post: 11902008
Originally Posted by FullWings
I think it needs to be said again that pretty much anything can happen to the aircraft systems and the engines will carry on running - this is by design as they have independent FADEC and power supplies and at sea level fuel will get through without boost pumps. You could almost saw the wing off the fuselage and the engine would still produce thrust, TCMA notwithstanding.
Yes, thanks, I've seen a few comments to this effect, and I have to accept most of what you say. I understand that they have their own dedicated generators and local independent FADECs (or EECs), but I'm trying to use what I do know to attempt to figure this out. I know that there are Fuel Cutoff switches in the cockpit. Somehow, if switched to Off, these will cut off the fuel to the engines, "no matter what". Of course, even that's not true, as the Qantas A380 engine burst apparently (comment in this thread) showed.

Anyway, the thing I'm looking at is how the fuel cutoff switch function could have been activated in some other way. To me, it seems obvious that there are wires that run between the engine fuel shutoff valves and the cockpit / flight control panel (no doubt with relays etc in between). I don't know where those shutoff valves are located, but logic says they should be located in the fuselage, not out at the engines. I also don't know how those valves operate - are they solenoid valves or electro-mechanically driven? Nor do I know where the power to activate those valves comes from, but using my logic, if those valves close when powered off, such as solenoid valves typically do, then the power cannot exclusively come from the engine-dedicated generators. If it did, you'd never be able to start the engines so they could supply their own power to hold those valves open. So, there must be some power (appropriately) fed from the main aircraft control bus to activate those valves - if the rest of what I'm assuming is correct. Anyway, like I say, I don't know enough about the details at this point, but there are many more ways to activate or deactivate a circuit than by flicking a switch. Killing the relevant power supply, for example. A screwdriver across some contacts (for example), another. Shorting a wire to Chassis, maybe. Just trying to contribute what I can.

You raise another interesting point: "TCMA notwithstanding". Could you elaborate, please? What will happen if the TCMA system, which apparently also has some degree of engine control, loses power? The problem with interlinked circuits and systems is that sometimes, unexpected things can happen when events that were not considered actually happen. If one module, reporting to another, loses power or fails, sometimes it can "tell" the surviving module something that isn't true... My concern is where does the power to the Fuel Cutoff switches come from? Are there relays or solid-state switches (or what?) between the Panel Switches and the valves? If so, is the valve power derived from a different source, and if so, where? Are the valves solenoids, open when power applied, or something else? What is the logic involved, between switch and valve?

Would you mind answering these questions so I can ponder it all further, please? If I'm wrong, I'll happily say so.

Originally Posted by FullWings
We don\x92t know yet what actually triggered the RAT from the relatively short list but every item on it means there is a serious/critical failure(s). The flight path suggests that it was a double engine failure or shutdown (commanded or uncommanded) as anything else should have left the aeroplane in a poor state but able to climb away.
100%

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aeo
2025-06-15T01:21:00
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Post: 11902026
Originally Posted by Compton3fox
It's controlled by Software and I've seen enough very weird "corner case" bugs that I discount nothing when Software is involved. I am sure there are more likely explanations why all power was lost (Assuming that was the case) but nothing would surprise me!
So are we now saying total loss of AC power for the RAT activation and activation of TCMA on two very independent engines for the power loss? What are the chances..

I can buy the AC power loss, but TCMA activation as well - That\x92s a stretch. TCMA is available on the ground and on approach and will activate if the engine thrust doesn\x92t follow the Thrust Lever command. On the ground it will shut the engine down (think RTO with engine stuck at T/O). On approach it will reduce the thrust if the engine doesn\x92t respond to the Thrust Lever command ala Cathay Pacific A330 (CMB - HKG) with the fuel contamination incident.

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TheFlyingNosh777
2025-06-15T01:35:00
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Post: 11902035
Hello,

I joined today to comment on this thread. I have read about 90% of the posts. Not 100%--apologies if I repeat somthing already discussed.

My daily driver is a 777.

--All of discussion regarding the previous leg and IFE / pack issues is highly unlikely to be related to the accident. IFE is installed in such a way it is isolated from AC systems (unless AI had it installed in the same manner as SwissAir 111) The AC may have been hot and possibly 1 pack was inop. (Could have been other reasons for warm interior temps) bMEL requires 1 of 2 operational. The previous sector people were breathing so 1 pack was working. Again, a pack issue is unlikely to be related to the accident.

--Fuel cut offs / possibly intentional?

--Please refrain from "any pilot would have firewalled the throttles, no pilot would ever...." There are so many accidents where pilots did things which are unfathomable. AirFlorida 90--if the thrust had been simply increased the plane would have flown normall / the Aeroflot crashes when the pilot allowed his teen son to play pilot, another where one pilot dared the other he could land with his eyes closed (or blind folded) / the airliner.that made a complete take off with the configuration horn blaring from the start of the TO run / Colgan 3407 stickshaker and stall but the Capt commands full up elevator / i could go on and on

--APU on for every TO. NO!!! Waste of fuel, higher maintenance costs due to more run time ect. Partnair 394 crash due to APU running in flight (lots of swiss cheese--too much to go over here)


Last edited by T28B; 15th Jun 2025 at 03:02 . Reason: the s word

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bakutteh
2025-06-15T02:13:00
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Post: 11902053
Devil Pprune Mind Traps from overwhelming posts

Do not discount the mistaken early flap retraction scenario too easily. Mull on this:

PF commanded gear up on attaining positive rate of climb, fixating on the HUD.
PM mistakenly raise flap lever from 5 to Flap 1 gate. Thrust reduced to Climb Thrust. Landing gear remained deployed. Massive loss of lift misidentified as loss of thrust. If any one pilot just had a dual engine failure scenario on a recent sim ride, brain and muscle memory would jump to loss of thrust in dual engine, prompting them to accomplish the recall memory items which called for both engine fuel control switches to CUTOFF and then RUN, and physically deployed the RAT.

There would be immediate loss of thrust with the engine taking time to recover , if at all, at such low airspeed!
The rest is left for Ppruners’ imagination.😖🥴😬

Last edited by bakutteh; 15th Jun 2025 at 09:18 .

11 users liked this post.

fdr
2025-06-15T02:24:00
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Post: 11902058
Originally Posted by BugBear
Consider losing one engine on the Dream. If it is a generator that's failed let's say #2 . Do the electric fuel pumps lose power? Only in #2? Does the mechanical pump start feeding right away? If so, is there a lull? Are both engines fuel pumps supplied off one Gen?

See I think there was no simultaneous loss of both 1, 2.
The odds give me a migraine. I still wonder if TCMA knows the difference between parked, rolling, rotated brakes and stowed. Only parenthetically, it didn't do this
The video is suitably clear to show that one engine DID NOT lose thrust before the other engine. The yaw rate authority in the FCS is going to input rudder immediately a failure of an engine occurs, (the 787 asymmetry architecture is quite different to the TAC on the B777) and so a rudder deflection would be evident. The video from the rear is ideally positioned to show a rudder deflection, and one would have been required, or a roll would have eventuated. Being FBW, the ailerons and asymmetric roll spoilers would be actuated to maintain the aircrafts attitude without any input by the crew if there is no roll rate command given by the control column (this is slightly different to the B777 as well).

The Thrust Control Malfunction Accommodation TCMA shuts down an engine when an idle asymmetry is detected . On the ground . With thrust levers at idle . The engine in question triggers the condition when it is above idle and not decelerating normally . That is multiple failure conditions that need to have occurred in the system to allow that to occur. It is nearly as wild a circumstance as the QFA 072 suspected cosmic bit flip, except that these are supposed to be independent systems. This does have the authority when the conditions exist to turn off the noise. That is the only reason it is a subject of interest.

The Thrust Asymmetry Protection gives a limited authority to reduce thrust on the surviving engine to maintain control. It would not trigger the conditions that the engines have gone silent, and hydraulics/electrics have been mussed up. That puts a spotlight on what has to go wrong on TCMA to get it to trigger outside of the conditions that it is intended to.

No yaw input, no roll input, no asymmetry. That leaves either both engines running at normal TO thrust or both having a simultaneous bad day out. Giving car keys to HAL 9000 can have some issues, and cosmic radiation is around a lot.

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Someone Somewhere
2025-06-15T02:36:00
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Post: 11902060
Originally Posted by BugBear
Difficult!? Maybe not. If very late the flaps were tagged stowed, and there was a simultaneous gear up command, with FlapDown command, the overload could have failed a GCS. Then it becomes a switching exercise. (Automatics).

Alarms Warnings Impacted EICAS, ETC. it happened long ago, but we know what happens when an engine driven generator quits ..first it bangs for awhile, then it burns itself up, then ...
Originally Posted by MaybeItIs
Thanks for answering the question I hadn't yet asked but wanted to confirm!

I'm still sticking with "Major Electrical Fault" as my most likely cause, and this adds to my suspicions.

As I understand it, the landing gear is raised / retracted by electric motor-driven hydraulic pump (pumps?). This/these would create a significant electrical load.

If the plane's multi-redundant electrical system has a fault which is intermittent (the worst kind of electrical issue to diagnose), and which causes the redundancy controls to go haywire (as there are, of course, electronic controls to detect failures and drive the switching over of primary and backup electrical supplies), then this fault could to triggered by a large load coming on-line. It could even be as simple as a high current cable lug not having been tightened when a part was being replaced at some stage. The relevant bolt might be only finger-tight. Enough to work 99.99% of the time between then and now... But a little bit more oxidation, and particularly, a bit more heat (it was a hot day), and suddenly, a fault.

Having worked in electronics for years, I know that semi-conductors (and lots of other components, especially capacitors [and batteries]) can also degrade instead of failing completely. Electro-static discharges are great for causing computer chips to die, or go meta-stable - meaning they can get all knotted up and cease working correctly - until they are powered off for a while. They can also degrade in a way that means they work normally a low temperatures, but don't above a certain temperature.

Anyway, there MUST be ways that the redundant power supplies can be brought down, simply because, to have a critical bus powered from a number of independent sources, there must be "controls" of some sort. I don't know how it's done in the 787, but that's where I'd be looking.

As there is a lot of discussion already about how the bogies are hanging the wrong way suggesting a started but failed retraction operation, and it's now confirmed that the retraction would normally have taken place at about the point where the flight went "pear shaped", I'm going to suggest that the two things are connected. More than that: I'll suggest that the Gear Up command triggered the fault that caused both engines to shut down in very short succession. Nothing the pilots did wrong, and no way they could have known and prevented it.

It's going to be difficult to prove though.
Gear and flaps are both hydraulic, and the hydraulic pumps typically act as effective fault-containment - a hydraulic failure or excess load doesn't result in excess demand on the electric side; the pump just starts to run out of output flow/pressure.

In addition, the 787 has four main generators and I believe the switching is segregated into at least two controllers, on top of the four separate generator control units.

And again, electrical failure should not cause engine failure - consider QF32 where the wiring to the engine was mostly severed and they had to drown it with a fire truck.

Originally Posted by ILS27LEFT
Best post until now in my view. We will find out very soon I think. Gear up command triggered the instant lack of fuel to both engines. I'm not sure on how the fuel flow is dependant on the power supplies on the 787 but I genuinely believe you are very very close to what might have happened here.
It's not. Boost pumps should be more-or-less unnecessary at sea level.

Originally Posted by MaybeItIs
Yes, thanks, I've seen a few comments to this effect, and I have to accept most of what you say. I understand that they have their own dedicated generators and local independent FADECs (or EECs), but I'm trying to use what I do know to attempt to figure this out. I know that there are Fuel Cutoff switches in the cockpit. Somehow, if switched to Off, these will cut off the fuel to the engines, "no matter what". Of course, even that's not true, as the Qantas A380 engine burst apparently (comment in this thread) showed.

Anyway, the thing I'm looking at is how the fuel cutoff switch function could have been activated in some other way. To me, it seems obvious that there are wires that run between the engine fuel shutoff valves and the cockpit / flight control panel (no doubt with relays etc in between). I don't know where those shutoff valves are located, but logic says they should be located in the fuselage, not out at the engines. I also don't know how those valves operate - are they solenoid valves or electro-mechanically driven? Nor do I know where the power to activate those valves comes from, but using my logic, if those valves close when powered off, such as solenoid valves typically do, then the power cannot exclusively come from the engine-dedicated generators. If it did, you'd never be able to start the engines so they could supply their own power to hold those valves open. So, there must be some power (appropriately) fed from the main aircraft control bus to activate those valves - if the rest of what I'm assuming is correct. Anyway, like I say, I don't know enough about the details at this point, but there are many more ways to activate or deactivate a circuit than by flicking a switch. Killing the relevant power supply, for example. A screwdriver across some contacts (for example), another. Shorting a wire to Chassis, maybe. Just trying to contribute what I can.

You raise another interesting point: "TCMA notwithstanding". Could you elaborate, please? What will happen if the TCMA system, which apparently also has some degree of engine control, loses power? The problem with interlinked circuits and systems is that sometimes, unexpected things can happen when events that were not considered actually happen. If one module, reporting to another, loses power or fails, sometimes it can "tell" the surviving module something that isn't true... My concern is where does the power to the Fuel Cutoff switches come from? Are there relays or solid-state switches (or what?) between the Panel Switches and the valves? If so, is the valve power derived from a different source, and if so, where? Are the valves solenoids, open when power applied, or something else? What is the logic involved, between switch and valve?

Would you mind answering these questions so I can ponder it all further, please? If I'm wrong, I'll happily say so.
I believe the valves are almost all bi-stable power-open power-close. When not powered, they remain in the last commanded position.

The valves are located in the spar (hence being called 'spar valves'. The fuel tank is immediately above the engine so it is a very short pipe for suction feeding. Tail mount engines are potentially a different story...

Originally Posted by lucille
What\x92s the usual time frame for the release of preliminary data and report from the FDR and CVR? Is it around 6 months?

I guess if no directives come from Boeing or the FAA in the next 2 weeks, it can be presumed that a systems failure from which recovery was impossible was unlikely.
A Prelimnary Report must be prepared within 30 days, but does not need to be public. May or may not have CVR/FDR data.

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BrogulT
2025-06-15T03:21:00
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Post: 11902071
Question

Originally Posted by bakutteh
Massive loss of lift misidentified as loss of thrust. If any one pilot just had a dual engine failure scenario on a recent sim ride, brain and muscle memory would jump to loss of thrust in dual engine, prompting them to accomplish the recall memory items which called for both engine fuel switches to OFF and then RUN, and physically deployed the RAT.
I keep reading this theory and I'm baffled. You think the PF is going to attempt a dual engine shutoff and relight during the initial climb based on a hunch that the engines have quit, all without even a sideways glance to see what N1 is or a short word with the PM?

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BrogulT
2025-06-15T03:53:00
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Post: 11902082
Originally Posted by fdr
If you are referring to loss of all boost pumps, am not aware of any engine that will not continue to run with a suction feed to the main boost pumps at low altitudes.
Is the ability of an engine to run using only suction feed ever actually checked or tested during operations or maintenance procedures?

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MaybeItIs
2025-06-15T04:00:00
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Post: 11902086
Originally Posted by Someone Somewhere
Gear and flaps are both hydraulic, and the hydraulic pumps typically act as effective fault-containment - a hydraulic failure or excess load doesn't result in excess demand on the electric side; the pump just starts to run out of output flow/pressure.
Ok, thanks for clarifying. Of course, an overload will simply cause the hydraulic pressure relief valves to activate. There will be a moderate increase in motor current when bypassing, but the electrical side should be fully able to cope with that. Should be! I'm suggesting here that there was a fault somewhere in the electrical supplies that effectively derated some part of it, and that maybe the GearUp load was too much for it on this occasion.

Originally Posted by Someone Somewhere
In addition, the 787 has four main generators and I believe the switching is segregated into at least two controllers, on top of the four separate generator control units.
Thanks for confirming the 4 gens. So there's probably quite a bit of switching required. Not sure how that's done, but I guess robust contactors are required. And even these can fail. Systems usually cannot tell that a contactor has failed on the open side until it's switched. So, a switchover may have been done, but a failed contact meant the backup generator wasn't connected. Who knows, so many possibilities.

Originally Posted by Someone Somewhere
And again, electrical failure should not cause engine failure - consider QF32 where the wiring to the engine was mostly severed and they had to drown it with a fire truck.
Sure, I agree, absolutely shouldn't. Yeah, the A380... Possibly (I suggest likely), the A380 uses different logic from the B787. In the Airbus case, maybe they prioritised keeping the fuel on over shutting it off in emergency. So, severing the Airbus Cutoff signal leaves the fuel on. Boeing may use the opposite priority, that Emergency Shutdown takes precedence over Engine Running, so cutting the signal turns the engine off. I don't know, but don't think the Airbus incident necessarily applies here.

Originally Posted by Someone Somewhere
It's not. Boost pumps should be more-or-less unnecessary at sea level.
I don't think either of us was debating that. I accept it as a fact.

Originally Posted by Someone Somewhere
I believe the valves are almost all bi-stable power-open power-close. When not powered, they remain in the last commanded position.

The valves are located in the spar (hence being called 'spar valves'. The fuel tank is immediately above the engine so it is a very short pipe for suction feeding. Tail mount engines are potentially a different story...
Okay! Many thanks for that! Of course, it very much complicates the picture, and I'm very puzzled as to how the Fuel Cutoff Switches and Valves operate. Apparently, the TCAM system shuts off an errant engine on the ground at least, but my concern is not with the software but the hardware. It obviously has an Output going into the Fuel Shutoff system. If the TCAM unit loses power, can that output cause the Cutoff process (powered by the engine-dedicated generator) to be activated? I guess that's the $64 billion question, but if MCAS is any example, then: Probably!