2025-06-29T18:07:00
permalink Post: 11913157
This has also been touched upon earlier in the thread, but it rather seems the cut-off switches are in the same LRU, in close proximity, using the same connector and goes through the same wiring harness. No one was able to say whether it works purely by digital signaling, and goes through any common software, or if it is duplicated by purely direct signaling. There might be numerous failure modes of the cut-off switch design, it is obviously very, very robust and overall sound, since dual failures here have never happened, but this is alredy an outlier event.
The fuel switches are located adjacent to each other; however all the wiring would be separate.
7 users liked this post.
2025-06-29T19:57:00
permalink Post: 11913194
Separate would seem to be a relative term, ofcourse wires are separated in some way, but how separate? Do they share a quick connect? Are there 2 separate looms each side of the throttle installation, or are thety in some twisted bundle together. Someone on this thread claimed the fuel cut offs where inhibited if the throttles weren\x92t in idle. Is this true? If so, is this a software or mechanical system?
Can anything so closely placed together be considered separate when looking at an outlier event?
Everyone is looking for something that would shut off both engines at the exact same time. This installation could, it is the closest the 2 systems get in proximity, physically and electrically, at least and it seems we don\x92t know a whole lot about it.
Can anything so closely placed together be considered separate when looking at an outlier event?
Everyone is looking for something that would shut off both engines at the exact same time. This installation could, it is the closest the 2 systems get in proximity, physically and electrically, at least and it seems we don\x92t know a whole lot about it.
Obviously, since the thrust levers are placed next to each other - the separation that's available in the center console is limited, but as soon as the wiring exits that constrained area, the separation increases. Furthermore, the same engine-to-engine wiring separation also applies to channel A/B FADEC channels, as well as the fuel switch/fire handle wiring.
All these requirements are documented in the Boeing DR&O (Design Requirements and Objectives) - and there is an audit done late in the design process to insure compliance.
In short, you're barking up a tree stump - there is nothing there.
12 users liked this post.
2025-06-30T03:42:00
permalink Post: 11913342
This has also been touched upon earlier in the thread, but it rather seems the cut-off switches are in the same LRU, in close proximity, using the same connector and goes through the same wiring harness. No one was able to say whether it works purely by digital signaling, and goes through any common software, or if it is duplicated by purely direct signaling. There might be numerous failure modes of the cut-off switch design, it is obviously very, very robust and overall sound, since dual failures here have never happened, but this is alredy an outlier event.
That's a pretty big "if" but here's the patent drawing:
2025-06-30T06:32:00
permalink Post: 11913383
Searching the web, I found out that regulations concerning new FDR require parameter 35g "fuel cut-off lever position" to be recorded. I also found that for a 2003 event with a 757, this was recorded (as was fuel flow).
I expect that this is also true for the 787. Can anyone confirm this?
I expect that this is also true for the 787. Can anyone confirm this?
2025-06-30T09:56:00
permalink Post: 11913487
Have the spring loaded Fuel Shut Off Valves been examined by GE on both engines???
2025-06-30T13:59:00
permalink Post: 11913644
There are several ways that the HPSOV can close:
An EEC (engine ECU) can close the upstream Fuel Metering Valve (FMV) electronically, so the HPSOV will lose its opening pressure.
The HPSOV can be acted on by a Shutoff Solenoid Valve (which directs fuel pressure in an opposite manner to the pressure coming from the Fuel Metering Valve).
Unfortunately, the diagram I am using is truncated, and I can't see if the Shutoff Solenoid Valve is magnetically latched in its last commanded position like typical fuel shutoff valves. Nor can I see what controls it. I suspect things like the respective cockpit fire handle and fuel cutoff lever, but also EEC commands.
There is probably a copyright on the diagram, so I won't post it here. Perhaps someone can fill in the gaps for me?
2025-06-30T15:49:00
permalink Post: 11913716
India's Minister of State for Civil Aviation appears to be confirming in this interview that the cause of the accident was a dual engine failure. Which is, I think, the first vaguely official confirmation of what happened that has been released? He also confirmed that all the data from the recorders has been downloaded and is being processed by the Indian AAIB, no boxes have been sent abroad.
The 30 day deadline for the preliminary report is July 12th.
The 30 day deadline for the preliminary report is July 12th.
The minister called the crash a \x93rare case\x94 and, referring to claims by veteran pilots and experts that a dual-engine failure may have led to the crash, said: \x93It has never happened that both engines have shut down together.\x94 \x93Once the report comes, we will be able to ascertain if it was an engine problem or fuel supply issue or why both engines had stopped functioning.
2025-06-30T21:18:00
permalink Post: 11913900
It would go against every aspect of training for a professional crew to deploy the rat below 400 feet. Further if you put 100 crewmembers in a simulator on takeoff and said deploy the rat manually I would bet not a single crew member could find the rat deploy switch and activate it in under 5 seconds and maybe 2 or 3 in 10 seconds.
It can auto-deploy in a significant electrical failure.
The theory I'm working is that, given the configuration of the aircraft, if there is a significant electrical failure (sufficient for the RAT to auto-deploy). The aircraft fuel pumps are lost. Approx. 7ish seconds after those fuel pumps are lost (if the engines are at TOGA), the fuel being received by the engines is arriving from a different source, a potentially contaminated source. I believe that the engine failure is a secondary result of the power loss (with specific circumstances).
But this all hinges on whether the engines were trying to run, or commanded off. Hence the request for interpretation of the sound.
1 user liked this post.
2025-06-30T22:04:00
permalink Post: 11913913
that, given the configuration of the aircraft
if there is a significant electrical failure (sufficient for the RAT to auto-deploy)
The aircraft fuel pumps are lost
the fuel being received by the engines is arriving from a different source
a potentially contaminated source
I believe that the engine failure is a secondary result of the power loss (with specific circumstances)
It isn't that your suppositions are necessarily bad ones, but that they seem a bit of a stretch. Of course I'm no expert, hence asking.
Last edited by za9ra22; 30th Jun 2025 at 22:19 .
2 users liked this post.
2025-06-30T22:21:00
permalink Post: 11913922
OK - Fair Challenges - good post, I'll have a go at answering and simultaneously expanding my own thoughts. In fact I'm not having a go at you, I'm more working my theory....
Experience. Without wishing to dox myself, I've worked in engineering at a major airline from apprentice through (in no particular order) Line Maintenance, Heavy and Light Maintenance, to technical support and maintenance control on both Boeing and Airbus products, with various qualifications and authorisations along the way. [Hmm - Scrap this sentence?]On the day 9/11 occurred, I should have been making modifications inside a fuel tank instead of staring at the TV with mouth on the floor.
However, I would describe my experience as broad, yet shallow in respect to this incident. Some of my fleet I know every rivet. Some of my fleet I've only ever seen from a distance. I don't touch airplanes for a living any more. B787 though - is not my area of specialty. I'll dig in, but am not the expert. I am not a systems design engineer, so precise numbers and flow rates, are not what I do. But what the systems do, how they operate, what they look like, smell and taste like... yeah, I'm not a muggle. And I do have access to all the manuals and know how to use them. And - let me be clear, I am speculating. I was advancing a theory. It WILL be some flavour of wrong. The investigation will reveal all.
I Agree, Water in fuel is not a novel concept. Aircraft fuel tanks attract water - fact. How much? It varies. I've sumped tanks and got no water, I've seen drops of water beading about in the bottom of a gallon jug, I've seen gallons of water. I've been so covered in fuel I cant smell it or think straight and taken gallon after gallon not being able to tell if its fuel or water. I also agree that 57% humidity doesn't seem particularly high - its not south east Asian jungle levels - but I'm not an expert at humidity, 32Deg c at 57% humidity at 02:30 am is not going to be comfortable for me though. I looked at recent weather in DEL, and those values were at the higher end of the range.
Further, I believe the prevailing weather conditions on the ground are less important when it comes to the volume of water getting in. Fuel is cold, or gets damn cold during a 9 Hr flight. Fuel Temperature Management is an issue for our Drivers. So as the fuel is used at altitude, Air enters the tank through NACA Ducts in the outboard end of the wing. Its beneficial to maintain a slight positive pressure, amongst other things to reduce evaporation. (Added complication, there is also the Nitrogen Enrichment system due to TWA800 - but that's more about processing the air in the tank to change the properties and make it non-explosive). Then as the aircraft descends, more air enters as the air pressure increases. Its the humidity of that air in the descent that is going to determine the volume of water entering the tank and potentially the fuel. The water in the air condenses on the sides of the tank because of the cold post-flight fuel. It doesn't dissolve into the fuel, but sinks to the bottom. Ground temperature / humidity and time will likely affect how much water condenses out of that air while on the ground. There won't be a huge amount of air exchange on the ground. Likely if the AC landed at 2am, then from sunrise as the tank warmed up, there would actually be a flow out of the vents.
What Features and procedures are there to mitigate Water? I apologise if my post gave the impression that there are no mitigation processes. There are. Water is well understood in the industry.
Well for a start, Features / Design. The Aircraft has a water scavenge system. Water doesn't mix with fuel, it sinks to the bottom being about 20% denser than fuel, so at the very lowest point in the tank, the water scavenge system (Powered by the Aft Fuel Pump through a jet pump, a venturi like system) will suck up the 'fluid' at the very lowest point, where the water would collect and in Boeings words 'drip' that fluid into the path of the pump pickup inlet (but I'd describe it more as a 'squirt'). The idea being that a small amount of water injected into the fuel will be consumed by the engines harmlessly.
There is also agitation. The wing tank pumps are pretty much running constantly, from before engine startup to after engine shutdown. The pumps are quite violent to the fuel and supply more pressure then the engine could ever need. Any excess pressure is dumped right back into the tank, quite close to the pump, in a direction that would further stir up the fuel and help break up any water into suspended droplets.
This all works if there is a small amount of water in the fuel. The water scavenge pickup is right next to the pump inlet, but a bit lower. Little bits of water get managed. Looking at the pictures of the system, I'd say a couple of gallons of water would do no harm at all.
But if there was significantly more water in that tank. Guessing 10-30 + gallons, then the pump would be circulating water, or highly water rich fuel.
Then there's the suction pickup. Its in the same 'bay' as the aft fuel pump and located a little 'higher' than the pump inlet and water scavenge inlet. But also located between stringers that can separate out the settled water ( I wish I could share the pictures, but more than my job is worth ) I can imagine the suction pickup being in a pool of 'stagnant' water.
I also saw a post from Metcha about the scavenge system blocking with Algae - I don't know about that (B787 not my fleet). But possible that could aggravate things. There's also the reports of the Indian AAIB looking at the Titan Biocide incident. Its possible that might be related and could modify the theory.
Procedures - There's the (at my airline weekly I think) procedure to 'sump' the tanks. There are drain points in the tank. Valves that you can push in with a tool and fluid drains. As described earlier (and videos exist on YouTube), you drain about a gallon of fluid and examine it for water. Most often in temperate climates (my experience), there's a few 'beads' of water in the bottom of the jug, moving about like mercury. Except when there's more. Sometimes there's a clear line in the jug, half water, fuel above. And sometimes a gallon of water, that smells like fuel. You drain it until you are sure there's no water.
Could 'that much' water have condensed in the tank? Well - There's the question. I guess the basis of the theory is that on descent into DEL, the wing tanks picked up some very humid air, which settled water into the tanks through the night. Then, as the theory I posited must work, the wing pumps must have circulated and suspended that water into the fuel.
By design, the water from the CDG-DEL arrival should have been consumed in the DEL-AMD Sector. But desperately clinging to defending my theory (I appreciate this is a hole), lets assume that at DEL the pumps were running for a long time. Lets assume that the pumps allowed the water to be dispersed within the tank prior to being used through the engines. Then - in the DEL-AMD sector, the wing tanks could have picked up more water.
How much water would cause a sustained flameout? I never posited a sustained flameout. I posited a significant reduction in thrust. Listening back to the rooftop video, which at first we were all listening for evidence of RAT, there's also a rhythmic pop-pop-pop of engines struggling. I think the engines were running, albeit badly. Heavily water contaminated fuel will do that. It doesn't have to be 100% water. Just enough water to make the engine lose thrust. Your 2 gallons per second figure assumes the engine running at full flow. I'm not a figures man, I'll not challenge that, I do recall flowmeters at max thrust spin like crazy. But an engine struggling due to a high perrcentage of contamination, is that using 2 gal/sec? or just trying to? What happens if there is e.g. 20% water in the fuel?
There are also reported incidents of engine flameout / thrust reduction that have all happened at altitude. Incidents that have been recovered due to the altitude and time available. I Posited that the engines would have eventually regained full thrust once the contamination worked though. But 30 seconds of rough engine is very different at 40,000 feet than it is at 100 feet.
The theory also relies on a second part - the electrical failure. That the electrical failure causes the fuel supply to switch, a few seconds after the failure. We go, at the point of electrical failure from a pumped centre tank supply to a sucked wing tank supply. It takes time for that different fuel to reach the engine.
Ive written enough and am tired. Must stop now.
Experience. Without wishing to dox myself, I've worked in engineering at a major airline from apprentice through (in no particular order) Line Maintenance, Heavy and Light Maintenance, to technical support and maintenance control on both Boeing and Airbus products, with various qualifications and authorisations along the way. [Hmm - Scrap this sentence?]On the day 9/11 occurred, I should have been making modifications inside a fuel tank instead of staring at the TV with mouth on the floor.
However, I would describe my experience as broad, yet shallow in respect to this incident. Some of my fleet I know every rivet. Some of my fleet I've only ever seen from a distance. I don't touch airplanes for a living any more. B787 though - is not my area of specialty. I'll dig in, but am not the expert. I am not a systems design engineer, so precise numbers and flow rates, are not what I do. But what the systems do, how they operate, what they look like, smell and taste like... yeah, I'm not a muggle. And I do have access to all the manuals and know how to use them. And - let me be clear, I am speculating. I was advancing a theory. It WILL be some flavour of wrong. The investigation will reveal all.
I Agree, Water in fuel is not a novel concept. Aircraft fuel tanks attract water - fact. How much? It varies. I've sumped tanks and got no water, I've seen drops of water beading about in the bottom of a gallon jug, I've seen gallons of water. I've been so covered in fuel I cant smell it or think straight and taken gallon after gallon not being able to tell if its fuel or water. I also agree that 57% humidity doesn't seem particularly high - its not south east Asian jungle levels - but I'm not an expert at humidity, 32Deg c at 57% humidity at 02:30 am is not going to be comfortable for me though. I looked at recent weather in DEL, and those values were at the higher end of the range.
Further, I believe the prevailing weather conditions on the ground are less important when it comes to the volume of water getting in. Fuel is cold, or gets damn cold during a 9 Hr flight. Fuel Temperature Management is an issue for our Drivers. So as the fuel is used at altitude, Air enters the tank through NACA Ducts in the outboard end of the wing. Its beneficial to maintain a slight positive pressure, amongst other things to reduce evaporation. (Added complication, there is also the Nitrogen Enrichment system due to TWA800 - but that's more about processing the air in the tank to change the properties and make it non-explosive). Then as the aircraft descends, more air enters as the air pressure increases. Its the humidity of that air in the descent that is going to determine the volume of water entering the tank and potentially the fuel. The water in the air condenses on the sides of the tank because of the cold post-flight fuel. It doesn't dissolve into the fuel, but sinks to the bottom. Ground temperature / humidity and time will likely affect how much water condenses out of that air while on the ground. There won't be a huge amount of air exchange on the ground. Likely if the AC landed at 2am, then from sunrise as the tank warmed up, there would actually be a flow out of the vents.
What Features and procedures are there to mitigate Water? I apologise if my post gave the impression that there are no mitigation processes. There are. Water is well understood in the industry.
Well for a start, Features / Design. The Aircraft has a water scavenge system. Water doesn't mix with fuel, it sinks to the bottom being about 20% denser than fuel, so at the very lowest point in the tank, the water scavenge system (Powered by the Aft Fuel Pump through a jet pump, a venturi like system) will suck up the 'fluid' at the very lowest point, where the water would collect and in Boeings words 'drip' that fluid into the path of the pump pickup inlet (but I'd describe it more as a 'squirt'). The idea being that a small amount of water injected into the fuel will be consumed by the engines harmlessly.
There is also agitation. The wing tank pumps are pretty much running constantly, from before engine startup to after engine shutdown. The pumps are quite violent to the fuel and supply more pressure then the engine could ever need. Any excess pressure is dumped right back into the tank, quite close to the pump, in a direction that would further stir up the fuel and help break up any water into suspended droplets.
This all works if there is a small amount of water in the fuel. The water scavenge pickup is right next to the pump inlet, but a bit lower. Little bits of water get managed. Looking at the pictures of the system, I'd say a couple of gallons of water would do no harm at all.
But if there was significantly more water in that tank. Guessing 10-30 + gallons, then the pump would be circulating water, or highly water rich fuel.
Then there's the suction pickup. Its in the same 'bay' as the aft fuel pump and located a little 'higher' than the pump inlet and water scavenge inlet. But also located between stringers that can separate out the settled water ( I wish I could share the pictures, but more than my job is worth ) I can imagine the suction pickup being in a pool of 'stagnant' water.
I also saw a post from Metcha about the scavenge system blocking with Algae - I don't know about that (B787 not my fleet). But possible that could aggravate things. There's also the reports of the Indian AAIB looking at the Titan Biocide incident. Its possible that might be related and could modify the theory.
Procedures - There's the (at my airline weekly I think) procedure to 'sump' the tanks. There are drain points in the tank. Valves that you can push in with a tool and fluid drains. As described earlier (and videos exist on YouTube), you drain about a gallon of fluid and examine it for water. Most often in temperate climates (my experience), there's a few 'beads' of water in the bottom of the jug, moving about like mercury. Except when there's more. Sometimes there's a clear line in the jug, half water, fuel above. And sometimes a gallon of water, that smells like fuel. You drain it until you are sure there's no water.
Could 'that much' water have condensed in the tank? Well - There's the question. I guess the basis of the theory is that on descent into DEL, the wing tanks picked up some very humid air, which settled water into the tanks through the night. Then, as the theory I posited must work, the wing pumps must have circulated and suspended that water into the fuel.
By design, the water from the CDG-DEL arrival should have been consumed in the DEL-AMD Sector. But desperately clinging to defending my theory (I appreciate this is a hole), lets assume that at DEL the pumps were running for a long time. Lets assume that the pumps allowed the water to be dispersed within the tank prior to being used through the engines. Then - in the DEL-AMD sector, the wing tanks could have picked up more water.
How much water would cause a sustained flameout? I never posited a sustained flameout. I posited a significant reduction in thrust. Listening back to the rooftop video, which at first we were all listening for evidence of RAT, there's also a rhythmic pop-pop-pop of engines struggling. I think the engines were running, albeit badly. Heavily water contaminated fuel will do that. It doesn't have to be 100% water. Just enough water to make the engine lose thrust. Your 2 gallons per second figure assumes the engine running at full flow. I'm not a figures man, I'll not challenge that, I do recall flowmeters at max thrust spin like crazy. But an engine struggling due to a high perrcentage of contamination, is that using 2 gal/sec? or just trying to? What happens if there is e.g. 20% water in the fuel?
There are also reported incidents of engine flameout / thrust reduction that have all happened at altitude. Incidents that have been recovered due to the altitude and time available. I Posited that the engines would have eventually regained full thrust once the contamination worked though. But 30 seconds of rough engine is very different at 40,000 feet than it is at 100 feet.
The theory also relies on a second part - the electrical failure. That the electrical failure causes the fuel supply to switch, a few seconds after the failure. We go, at the point of electrical failure from a pumped centre tank supply to a sucked wing tank supply. It takes time for that different fuel to reach the engine.
Ive written enough and am tired. Must stop now.
Last edited by Senior Pilot; 30th Jun 2025 at 23:01 . Reason: Quote from a week ago; this is not a Hamsterwheel thread, thanks!
2025-06-30T22:49:00
permalink Post: 11913931
Grounded Spanner
There's an awful lot of ifs and buts in that opus.
A water spillage from a galley or lavatory would have to be huge to cause the type of total electrical failure you describe. The Power Electrics panels are yards apart, for both main systems to fail simultaneously due to water ingress would take gallons and gallons of water. Sorry but I don't buy it!
Do they still use Bowsers in India? I thought most airports used underground pipes feeding pots on the stands.
Re: settled fuel. As soon as the boost pumps are running, fuel is being recirculated. When we do water drain checks we have to leave the aircraft for a good hour after any refuelling, boost pump operation or aircraft movement before taking the samples. Otherwise any water will remain suspended in the fuel.
Generally speaking flight deck preparation that I have witnessed will have the boost pumps on many many minutes before take off. This will agitate the fuel and any contamination sufficiently to render your theory moot .
I'm also not quite sure how the aircraft could have got so much contaminated fuel on the previous sector and it not be scavenged out during that flight.
There's an awful lot of ifs and buts in that opus.
A water spillage from a galley or lavatory would have to be huge to cause the type of total electrical failure you describe. The Power Electrics panels are yards apart, for both main systems to fail simultaneously due to water ingress would take gallons and gallons of water. Sorry but I don't buy it!
Do they still use Bowsers in India? I thought most airports used underground pipes feeding pots on the stands.
Re: settled fuel. As soon as the boost pumps are running, fuel is being recirculated. When we do water drain checks we have to leave the aircraft for a good hour after any refuelling, boost pump operation or aircraft movement before taking the samples. Otherwise any water will remain suspended in the fuel.
Generally speaking flight deck preparation that I have witnessed will have the boost pumps on many many minutes before take off. This will agitate the fuel and any contamination sufficiently to render your theory moot .
I'm also not quite sure how the aircraft could have got so much contaminated fuel on the previous sector and it not be scavenged out during that flight.
1 user liked this post.
2025-07-01T03:07:00
permalink Post: 11913998
787 Fuel System
).
On the A320 if the centre fuel pumps are selected on pre-start, they run for 2 mins after start and then turn themselves off until Flaps selected to 0 (i.e. well after takeoff), when they turn themselves on. As far as the crew are concerned they were selected on from pre-start onwards [long retired A320 so forgive me if in error].
If certification demands this 'complexity' it would seem surprising the 787 does not have a similar system? Are we sure the 787 centre tank 'higher pressure' pumps are:
- Actually running on takeoff?
- If running, they are providing centre tank fuel directly to both engines, and not, say, centre tank fuel to wing tanks, and then wing tanks to engines?
3 users liked this post.
2025-07-01T03:50:00
permalink Post: 11914009
Both engines run from the center tank on takeoff if it has fuel in the tank which was the case on this flight
\xa7 25.953 Fuel system independence.
Each fuel system must meet the requirements of \xa7 25.903(b) ( (b) Engine isolation. The powerplants must be arranged and isolated from each other to allow operation, in at least one configuration, so that the failure or malfunction of any engine, or of any system that can affect the engine, will not— (1) Prevent the continued safe operation of the remaining engines; or(2) Require immediate action by any crewmember for continued safe operation )
by—
(a) Allowing the supply of fuel to each engine through a system independent of each part of the system supplying fuel to any other engine; or
(b) Any other acceptable method
That is, during these periods each engine must be supplied with fuel from a separate tank, you don't want all engines being supplied by the same tank and run the risk of losing all engines due to contamination in that one tank.
Switch over to the centre tank to feed all engines typically takes place at 10,000'
1 user liked this post.
2025-07-01T06:45:00
permalink Post: 11914044
Perhaps a result of being too dense, in these threads I have not understood whatsoever the discussions on L/D, best glide, AOA, stall speed, angles, whatever, as being relevant to this flight. I assume that the pilot flying was flying, i.e. stick and rudder. I give him/her the benefit of the doubt on account of being a pilot. Professional or not.
The real question is why this happened when engines and their associated systems are, by design and regulation, as independent as possible. The top runners at the moment are (in no particular order): pilot action, simultaneous hardware/software malfunction and massive fuel contamination. They are all very unlikely (and cogent technical arguments can be made against each of them) but so is the event that followed.
2025-07-01T06:48:00
permalink Post: 11914048
Hold your horses there
Bloggs
, I didn't say they did, I said centre tanks were typically turned on at that altitude (using a certain 737 operator as a guide). As the check list that you posted shows the centre pumps will automatically turn off because of load shedding once an engine is started.
Once both engines are running and the four VFSGs are online, I would not expect any load shedding and certainly not of flight loads like fuel pumps.
The Airbus manuals imply or clearly state that centre pumps are inhibited when the flaps are extended, so both engines draw from the wing/main tanks. I haven't seen anything clearly matching in the Boeing manuals.
2025-07-01T08:49:00
permalink Post: 11914118
In my experience the APU supplies enough power to run all systems. Hydraulic pumps, fuel pumps etc
2025-07-01T09:32:00
permalink Post: 11914147
I know that the engine driven pumps have documented limitations and that the regulations allow for some limitations. I know that at least one of these limitation is high altitude and I _suspect_ that the design intends for this unlikely scenario (engine driven fuel pumps alone with no AC pumps) to guarantee enough fuel flow to get to an airport and land. I also suspect that the APU is expected to solve loss of all AC generators - and as we know, there wasn't enough time for it to start in this scenario.
2025-07-01T10:19:00
permalink Post: 11914164
Not really relevant to what you quoted though, as the scenario in question requires:
-
Engines running on centre tank fuel during takeoff
while the aircraft is operating normally
- We don't know for certain if this is the case. It seems to be but it's not something that happens on other families.
- Then, total AC failure stopping fuel boost pumps.
- Engines suction feed from contaminated/full-of-water wing tanks.
I also don't see any evidence that engine driven fuel pumps alone must be able to handle this scenario: provide enough fuel flow for takeoff and climb, even while the pitch is rotating, even in a hot environment with significant weight, even while the gear is stuck down.
I know that the engine driven pumps have documented limitations and that the regulations allow for some limitations. I know that at least one of these limitation is high altitude and I _suspect_ that the design intends for this unlikely scenario (engine driven fuel pumps alone with no AC pumps) to guarantee enough fuel flow to get to an airport and land. I also suspect that the APU is expected to solve loss of all AC generators - and as we know, there wasn't enough time for it to start in this scenario.
I know that the engine driven pumps have documented limitations and that the regulations allow for some limitations. I know that at least one of these limitation is high altitude and I _suspect_ that the design intends for this unlikely scenario (engine driven fuel pumps alone with no AC pumps) to guarantee enough fuel flow to get to an airport and land. I also suspect that the APU is expected to solve loss of all AC generators - and as we know, there wasn't enough time for it to start in this scenario.
The limitations at high altitude are primarily air/volatiles degassing out of the fuel. That's not going to be much of an issue at sea level, even if the engines are a bit higher up during rotation.
APU is a nice-to-have; it's on the MEL. If you lose all four generators, it's because of some major carnage in the electrical software/hardware and chances of putting the APU on line even if it's operating are very slim.
1 user liked this post.
2025-07-01T12:10:00
permalink Post: 11914226
It's exactly the same on the B777 - the centre fuel pump switches go on before start if the FUEL IN CENTER EICAS message is displayed. The switches go off again when the FUEL LOW CENTER message is displayed. On the ground, the B777 needs two power sources for both centre tank pumps to operate, so one pump is normally shed until after engine start. The centre tank pumps output about three times the pressure of the main tank pumps. Fuel is fed from the centre tank until the centre tank pumps are selected off.
2025-07-01T12:20:00
permalink Post: 11914234
Originally Posted by
MaybeItIs
...\xa7 25.903(b) includes the words: "in at least one configuration,"
It doesn't, that I can see, state that that configuration must be used during takeoff, though common sense would say it should.
...\xa7 25.903(b) includes the words: "in at least one configuration,"
It doesn't, that I can see, state that that configuration must be used during takeoff, though common sense would say it should.
I also don't see any evidence that engine driven fuel pumps alone must be able to handle this scenario: provide enough fuel flow for takeoff and climb, even while the pitch is rotating, even in a hot environment with significant weight, even while the gear is stuck down.
A lot of other posters here have stated that according to FCOM instructions, the normal, accepted 787 Takeoff configuration is "Both sides draw from centre" if the Centre tanks have enough fuel in them. I think (maybe wrongly) that this (prior few posts) is the first time this exact point has been raised. I hope I'm correct there. If not, my humble apologies.
The great thing about this forum and sadly, this tragic accident, is that it's drawing a few previously little-known worms out of the woodwork.
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