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Pinkman
2025-06-20T01:43:00 permalink Post: 11906532 |
User989 thanks for a nice summary
I am at risk of turning into one of those folks who gets their mind locked on one possibility and keeps banging on about it but here goes; If the authorities determined that the accident aircraft had been treated by maintenance for microbial growth in the fuel tanks within the last week or so, and they suspected that that procedure was carried out in a way that could result in fuel contamination, then that would explain 1/ No other aircraft being affected 2/ No measures taken at the airport 3/ No AD\x92s from the regulators 4/ No grounding of 787\x92s 5/ Flight profile 6/ Rat deployment etc etc I agree with your statement that dual flameout due fuel contamination is very unlikely, but we ARE dealing with something that is very unlikely. I favour the theory because an error in treating the fuel is so predictably human and simple, and a dual engine failure being related to fuel is also a simple and obvious idea, and it satisfies all we know both about the aircraft\x92s behaviour, and the authorities behaviour post accident. I posted a report earlier of a 787-8 powered by the same engine type have both engines roll back sub-idle within a minute of each other while airborne due to this, so we know it can happen in theory. Now\x85\x85I want to be clear that I\x92m not saying I think I know what happened, I\x92m an average Joe with my hands full just flying the line, but I am a bit surprised that the idea of \x91fuel contamination specific to that airframe\x92 doesn\x92t get discussed more on this thread. Thanks again for the clear summary of discussion thus far. Last edited by Pinkman; 20th Jun 2025 at 02:32 . 7 users liked this post. |
Furr
2025-06-20T07:31:00 permalink Post: 11906655 |
If power failed first?
If power failed first,
What happens to TCMA sensors like Weight on Wheels? Radio altimeter? Is there one Weight on Wheels per engine? Is there one radio altimeter per engine? If not, why not? Are the TCMA sensors directly powered as part of FADEC? If not, why not? Is it possible that there was a noticeable loss of thrust caused by loss of fuel pumps and the pilot responded by cycling thrust to zero and back, trying to clear the problem, inadvertently triggering the TCMA? 1 user liked this post. |
sSquares
2025-06-20T10:59:00 permalink Post: 11906833 |
II.
Fuel-related
1. Loss of electric fuel pumps
Suction feed would have provided sufficient fuel pressure.
2. Fuel contamination
No other aircraft affected, no measures taken at airport. Simultaneous flameout due to contaminated fuel very unlikely.
3. Vapour lock
Unlikely to occur in this scenario. Even if (momentarily) no sufficient fuel pressure from the center tank, the engines would have been fed by the wing tanks.
1 user liked this post. |
Mechta
2025-06-20T11:09:00 permalink Post: 11906844 |
There are numerous pictures ot the outside of B787 centre tanks on the net. Does anyone one have any internal pictures, showing the tank floor and fuel pump pick ups?
We know the engines lost power in the initial climb, shortly after rotation. If there was water sitting between the tank lower skin stringers, the rotation would have been the point that the water could tumble over the stringers that were previously preventing its movement. accumulate at the back of the tank and enter both pumps more or less simultaneously. For background, I worked at Smiths Industries wet fuel testing the B777 gauging system on ground rigs, and at Airbus building and testing fuel tank inerting rigs. I've seen inside Airbus tanks, but not Boeing. 2 users liked this post. |
OPENDOOR
2025-06-20T11:17:00 permalink Post: 11906850 |
Remote DiagnosticsThis engine health monitoring is incorporated GE Aerospace’s self-service customer web portals, where customers can find technical updates and analysis of key engine performance trends such as oil usage, gas temperatures, vibration, rotor speed, fuel flow and more. In addition, Customer Notification Reports (CNRs) issued to GE Aerospace customers identify potential engine issues with recommended maintenance actions. The comprehensive service includes dedicated consultations for analysis of key engine performance trends to optimize fleet operations as well customized insights and maintenance recommendations.https://www.geaerospace.com/commerci...ital-solutions |
Squawk7700
2025-06-20T11:20:00 permalink Post: 11906855 |
There are numerous pictures ot the outside of B787 centre tanks on the net. Does anyone one have any internal pictures, showing the tank floor and fuel pump pick ups?
We know the engines lost power in the initial climb, shortly after rotation. If there was water sitting between the tank lower skin stringers, the rotation would have been the point that the water could tumble over the stringers that were previously preventing its movement. accumulate at the back of the tank and enter both pumps more or less simultaneously. In a well designed boat, you'd have each engine feeding from a different tank for the utmost in redundancy, but seemingly not so in all aircraft. |
violator
2025-06-20T11:29:00 permalink Post: 11906865 |
I had been wondering the same until I read that there is a forward and a rear pickup within the tank. Each pump in the centre tank draws from it's own pickup and is piped to the spar valves and then onto the engines.
In a well designed boat, you'd have each engine feeding from a different tank for the utmost in redundancy, but seemingly not so in all aircraft. |
Squawk7700
2025-06-20T11:34:00 permalink Post: 11906868 |
Interestingly enough on Airbus aircraft even when there\x92s fuel in the centre tank the centre tank fuel pumps are switched off automatically after the flaps are extended for takeoff and each engine is fed by its respective wing tank for takeoff. Surprised it\x92s not the case for Boeings
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Mechta
2025-06-20T11:46:00 permalink Post: 11906879 |
Interestingly enough on Airbus aircraft even when there\x92s fuel in the centre tank the centre tank fuel pumps are switched off automatically after the flaps are extended for takeoff and each engine is fed by its respective wing tank for takeoff. Surprised it\x92s not the case for Boeings
|
Crossky
2025-06-20T21:16:00 permalink Post: 11907327 |
Hello, this is my first post on pprune; as a 787 pilot I’m also puzzled by this accident. All seem to agree that for some reason there was a complete electrical failure and RAT deployment. With a complete electrical failure all six main fuel pumps fail. Each engine also has two mechanically driven fuel pumps. On takeoff, if there is fuel in the center tank, it will be used first, pumped by the two center tank pumps.
My airline’s manuals don’t go into much detail, but I read on another site that if both the center tank pumps fail, the engine driven pumps aren’t able to suction feed well enough from the center tanks to sustain engine operation. If there was fuel in the center tanks, a complete electrical failure would soon lead to center tank fuel pumps failure (all fuel pumps failure as stated previously) and fuel starvation of both engines. A rescue from this situation would be an immediate selection of both center tank fuel pumps OFF (not if my airline’s non-normal checklists) and waiting for successful suction feed from the L and R main tanks to occur, this would take a number of seconds. 4 users liked this post. |
MaybeItIs
2025-06-20T22:57:00 permalink Post: 11907382 |
Hello, this is my first post on pprune; as a 787 pilot I\x92m also puzzled by this accident. All seem to agree that for some reason there was a complete electrical failure and RAT deployment. With a complete electrical failure all six main fuel pumps fail. Each engine also has two mechanically driven fuel pumps. On takeoff, if there is fuel in the center tank, it will be used first, pumped by the two center tank pumps.
My airline\x92s manuals don\x92t go into much detail, but I read on another site that if both the center tank pumps fail, the engine driven pumps aren\x92t able to suction feed well enough from the center tanks to sustain engine operation. If there was fuel in the center tanks, a complete electrical failure would soon lead to center tank fuel pumps failure (all fuel pumps failure as stated previously) and fuel starvation of both engines. A rescue from this situation would be an immediate selection of both center tank fuel pumps OFF (not if my airline\x92s non-normal checklists) and waiting for successful suction feed from the L and R main tanks to occur, this would take a number of seconds. FWIW, according to earlier posts, the fuel load was about 50T, leaving about 18T in the centre tank, so (I think) about 25-30% full. A full centre tank might allow engine pump suction to work fine, but this might not? (Contrary to what some have said.) Anyway, FWIW, not everyone agrees with RAT Deployment - see recent post by shep69. Would love to know why he doesn't go with RAT deployment... |
EDML
2025-06-20T23:08:00 permalink Post: 11907388 |
Hello, this is my first post on pprune; as a 787 pilot I\x92m also puzzled by this accident. All seem to agree that for some reason there was a complete electrical failure and RAT deployment. With a complete electrical failure all six main fuel pumps fail. Each engine also has two mechanically driven fuel pumps. On takeoff, if there is fuel in the center tank, it will be used first, pumped by the two center tank pumps.
My airline\x92s manuals don\x92t go into much detail, but I read on another site that if both the center tank pumps fail, the engine driven pumps aren\x92t able to suction feed well enough from the center tanks to sustain engine operation. If there was fuel in the center tanks, a complete electrical failure would soon lead to center tank fuel pumps failure (all fuel pumps failure as stated previously) and fuel starvation of both engines. A rescue from this situation would be an immediate selection of both center tank fuel pumps OFF (not if my airline\x92s non-normal checklists) and waiting for successful suction feed from the L and R main tanks to occur, this would take a number of seconds. Furthermore the preference of the center tank while it's filled is just by the higher fuel pressure those center pumps deliver. There is no valve that controls that, which might be triggered by switching off pumps. 8 users liked this post. |
Seamless
2025-06-20T23:18:00 permalink Post: 11907389 |
Sorry but that doesn't really make sense. Once the power failed and all pumps are off where is the point of switching of the center fuel pumps off? Without power they aren't running anyways.
Furthermore the preference of the center tank while it's filled is just by the higher fuel pressure those center pumps deliver. There is no valve that controls that, which might be triggered by switching off pumps. |
KingAir1978
2025-06-21T00:26:00 permalink Post: 11907405 |
Hello, this is my first post on pprune; as a 787 pilot I’m also puzzled by this accident. All seem to agree that for some reason there was a complete electrical failure and RAT deployment. With a complete electrical failure all six main fuel pumps fail. Each engine also has two mechanically driven fuel pumps. On takeoff, if there is fuel in the center tank, it will be used first, pumped by the two center tank pumps.
My airline’s manuals don’t go into much detail, but I read on another site that if both the center tank pumps fail, the engine driven pumps aren’t able to suction feed well enough from the center tanks to sustain engine operation. If there was fuel in the center tanks, a complete electrical failure would soon lead to center tank fuel pumps failure (all fuel pumps failure as stated previously) and fuel starvation of both engines. A rescue from this situation would be an immediate selection of both center tank fuel pumps OFF (not if my airline’s non-normal checklists) and waiting for successful suction feed from the L and R main tanks to occur, this would take a number of seconds. On the 320 (equipped with the old system (fuel pumps), not the newer system (transfer valves)) the center tank pumps are inhibited when the airplane is airborne with the slats extended. Check these certification rules: https://www.ecfr.gov/current/title-14/section-25.953 and https://www.ecfr.gov/current/title-1...-25#p-25.903(b ) 1 user liked this post. |
fdr
2025-06-21T01:04:00 permalink Post: 11907425 |
Hello, this is my first post on pprune; as a 787 pilot I\x92m also puzzled by this accident. All seem to agree that for some reason there was a complete electrical failure and RAT deployment. With a complete electrical failure all six main fuel pumps fail. Each engine also has two mechanically driven fuel pumps. On takeoff, if there is fuel in the center tank, it will be used first, pumped by the two center tank pumps.
My airline\x92s manuals don\x92t go into much detail, but I read on another site that if both the center tank pumps fail, the engine driven pumps aren\x92t able to suction feed well enough from the center tanks to sustain engine operation. If there was fuel in the center tanks, a complete electrical failure would soon lead to center tank fuel pumps failure (all fuel pumps failure as stated previously) and fuel starvation of both engines. A rescue from this situation would be an immediate selection of both center tank fuel pumps OFF (not if my airline\x92s non-normal checklists) and waiting for successful suction feed from the L and R main tanks to occur, this would take a number of seconds. If you go and chat to the engineers, have a look in the IPC or MM I Ch 28, you should find a good description of the fuel boost pumps. It's been a while but I recall they are Eaton designs, the general arrangement is similar to the B777. They both have a suction feed that permits fuel feed in the event of a loss of all boost pumps. The only impact of that arises at high altitude and high thrust levels, where the engine driven fuel boost pumps may capitate and reduce the available fuel feed resulting in a lower thrust level. Refer page 12.20.02 in the TBC's B787 FCTM, or search for "SUCTION FEED". At sea level, full thrust will be achieved without any boost pump on the aircraft. Recall that the CWT boost pumps are known as Override boost pumps, they are feeding from the CWT when there is fuel and they are running, as the output pressure is higher from these pumps than the 2 wing boost pumps. Whether there is fuel in the CWT or not, or the CWT pumps are energised, is immaterial to whether fuel will be supplied to the engine driven fuel pumps. Note that with BA038, the fundamental problem was blockage of wax/ice formed in the piping that blocked the FOHE, and that will cause a problem with those engines that have such architecture, but is not associated with the availability of the boost pumps themselves. Even then, the engines did not technically fail, as they have both done simultaneously with the B788 of AI 171, BA's engines were running but not able to provide significant thrust due to the FOHE blockages. ![]() ![]() ![]() 4 users liked this post. |
Crossky
2025-06-21T02:51:00 permalink Post: 11907453 |
Under a complete electrical failure all electrically powered fuel pumps will fail, but the engine driven mechanical pumps will not fail, but according to information in my manual and what I\x92ve seen online, the engine driven pumps can only suction feed the engines from the main tanks. The 787 will burn fuel from the center tanks first, because they provide a greater pressure than the main fuel tank pumps.
3 users liked this post. |
Aerospace101
2025-06-21T12:15:00 permalink Post: 11907698 |
Commanded engine cutoff - the aisle stand fuel switch sends electrical signals to the spar valve and the "High Pressure Shutoff Valve" (HPSOV) in the Fuel Metering Unit, commanding them to open/close using aircraft power.
The HPSOV is solenoid controlled, and near instantaneous. The solenoid is of a 'locking' type that needs to be powered both ways (for obvious reasons, you wouldn't want a loss of electrical power to shut down the engine)
. The fire handle does the same thing, via different electrical paths (i.e. separate wiring).
.
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. |
EDML
2025-06-21T12:30:00 permalink Post: 11907705 |
Without going round the hamsterwheel again does anyone have an actual reference for this? Because I've gone back through each of tdracer's very informative posts about this
see here
and there is a discrepancy in the two points he makes below in adjacent posts. Is tdracer talking about the same HPSOV valves? Can anyone confirm that with both AC power loss and and a temporary DC power loss there are no critical engine related shutoff valves that will fail safe (unpowered) in a closed position?
However, it could easily have different modes of operation (closed, electrically actuated), activated (electrically actuated), open (transition from activated + fuel pressure > 300psi). 4 users liked this post. |
Feathers McGraw
2025-06-21T13:50:00 permalink Post: 11907772 |
Hello, this is my first post on pprune; as a 787 pilot I’m also puzzled by this accident. All seem to agree that for some reason there was a complete electrical failure and RAT deployment. With a complete electrical failure all six main fuel pumps fail. Each engine also has two mechanically driven fuel pumps. On takeoff, if there is fuel in the center tank, it will be used first, pumped by the two center tank pumps.
My airline’s manuals don’t go into much detail, but I read on another site that if both the center tank pumps fail, the engine driven pumps aren’t able to suction feed well enough from the center tanks to sustain engine operation. If there was fuel in the center tanks, a complete electrical failure would soon lead to center tank fuel pumps failure (all fuel pumps failure as stated previously) and fuel starvation of both engines. A rescue from this situation would be an immediate selection of both center tank fuel pumps OFF (not if my airline’s non-normal checklists) and waiting for successful suction feed from the L and R main tanks to occur, this would take a number of seconds. Further up the thread one of the posters mentions that it is very unlikely that any crew action (checklist, QRH) would have got anywhere near to changing a fuel pump switch position. |
Capn Bloggs
2025-06-21T15:02:00 permalink Post: 11907823 |
Originally Posted by
Feathers MGraw
Is this something that you train for in your airline? Am I correct that to do this requires making the needed switch selections on the overhead panel?
Further up the thread one of the posters mentions that it is very unlikely that any crew action (checklist, QRH) would have got anywhere near to changing a fuel pump switch position. Your comment:
​​​​​​​
it is very unlikely that any crew action (checklist, QRH) would have got anywhere near to changing a fuel pump switch position.
5 users liked this post. |
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