June 21, 2025, 21:37:00 GMT
permalink Post: 11908084
Why should it? It\x92s part of the FADEC as are the TLA sensors.
June 22, 2025, 00:15:00 GMT
permalink Post: 11908173
I don't want to refute your theory, but given your 30 years of experience---presuming it is relevant--I'd ask you to clarify a few things.
First, water in fuel is not a novel concept and I would presume that the designers of the 787 knew about it. You've simply stated that water might collect and settle out, but how much water might you expect under those conditions (57% humidity doesn't seem terribly high to me) and what features and procedures are already there to mitigage water contamination issues? Your theory would imply that there basically aren't any. IDK how the tank venting system works, but the idea that some huge amount of water could have condensed in the tank from the outside seems preposterous.
Second, how much water do you think it would take to cause a sustained flameout in one of those engines? Remember that they have automatic continous relight, so you're going to have to sustain your flame suppression long enough for them to wind down completely. I think those engines were probably using something like 2 gallons per second of fuel along with 250lbs of air heated to over 1100F. Any fuel in the mix would burn and the water would be converted to steam so you'd need mostly water for a long time. So if you think a hundred gallons of water could have gotten into each tank then perhaps I'd buy your theory--which, btw, does fit the known facts pretty well. But I think that short of some woeful neglect, Boeing and AI already know about and have methods of dealing with water contamination. At least I hope so.
First, water in fuel is not a novel concept and I would presume that the designers of the 787 knew about it. You've simply stated that water might collect and settle out, but how much water might you expect under those conditions (57% humidity doesn't seem terribly high to me) and what features and procedures are already there to mitigage water contamination issues? Your theory would imply that there basically aren't any. IDK how the tank venting system works, but the idea that some huge amount of water could have condensed in the tank from the outside seems preposterous.
Second, how much water do you think it would take to cause a sustained flameout in one of those engines? Remember that they have automatic continous relight, so you're going to have to sustain your flame suppression long enough for them to wind down completely. I think those engines were probably using something like 2 gallons per second of fuel along with 250lbs of air heated to over 1100F. Any fuel in the mix would burn and the water would be converted to steam so you'd need mostly water for a long time. So if you think a hundred gallons of water could have gotten into each tank then perhaps I'd buy your theory--which, btw, does fit the known facts pretty well. But I think that short of some woeful neglect, Boeing and AI already know about and have methods of dealing with water contamination. At least I hope so.
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.
June 22, 2025, 00:41:00 GMT
permalink Post: 11908191
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.
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 percentage 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.
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 percentage 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.
Not sure if you are right, and not familiar enough with 787 to check the fuel flow logic, but a friend of mine dead-sticked a single engine trainer into a field due to water in the fuel ... 20 minutes after takeoff.
It could have happened earlier.
June 22, 2025, 16:37:00 GMT
permalink Post: 11908670
In reverse order, and the first one being very speculative: The type of battery will likely be highly specific for the usecase, here rugged before anything else. Likely specialized chemistry or one of those hybrid solid state ones. Commonly they trade capacity for other features.
Regarding the recording feature, there's three types of microphone commonly used nowadays: Condenser and Ribbon type are somewhat fragile and require power to record audio while Dynamic type is basically a reverse speaker and is considered rugged. There's an off chance that a Piezzo microphone would be used here as they are basically indestructible but usually reserved for recording while in contact with a large sound transducer. My guess based on that is that we're looking at a dynamic microphone with a run of the mill preamp.
Depending on the actual electric setup this would yield a handful of different possible installations:
1) The "Cockpit Area Microphone" (hereby christened CAM because I like abbreviations) is a self contained unit consisting of a Microphone, a preamp and AD converter. This would mean while provided power the digital recording could be passed to either EAFR.
2) The CAM is a self contained unit consisting of a Microphone and a preamp. This would mean while provided power it could send an analog audio signal to the forward EAFR no problem, but would potentially struggle generating enough of a signal to be picked up by the rear EAFR.
3) The CAM is just a Microphone. This would mean it requires either no or very little power (even Condenser Mics usually require only Milliwatts) but the signal would be very hard to send over long distances and would require the EAFR to have a preamp.
In general it is audio engineering 101 to place a preamp as close to the source as possible to avoid noise. Thus I would rule out 3. It has both ups and downs to convert the analog signal to a digital signal, and there is a possibility they'd do both. In either case I am confused from an audio engineering standpoint why the rear EAFR would not pickup audio from the CAM if the forward EAFR does. Unless the rear EAFR is fed (audio) data only via BUS, which would be an interesting choice.
Also keep in mind that historically the CVR was also located in the tail section and very much received an analog signal over the entire distance. There's really no technical reason this wouldn't be possible, I routinely use far longer cables when running audio signals at concerts and those can't use compression because it would dumpster sound quality.
So, yeah, I don't understand why there would be a mismatch between the recordings of either EAFR, unless there was something else preventing all signal transmission towards the rear EAFR. The CVR in the rear has been a thing for 80 years now.
Regards,
Justus
Regarding the recording feature, there's three types of microphone commonly used nowadays: Condenser and Ribbon type are somewhat fragile and require power to record audio while Dynamic type is basically a reverse speaker and is considered rugged. There's an off chance that a Piezzo microphone would be used here as they are basically indestructible but usually reserved for recording while in contact with a large sound transducer. My guess based on that is that we're looking at a dynamic microphone with a run of the mill preamp.
Depending on the actual electric setup this would yield a handful of different possible installations:
1) The "Cockpit Area Microphone" (hereby christened CAM because I like abbreviations) is a self contained unit consisting of a Microphone, a preamp and AD converter. This would mean while provided power the digital recording could be passed to either EAFR.
2) The CAM is a self contained unit consisting of a Microphone and a preamp. This would mean while provided power it could send an analog audio signal to the forward EAFR no problem, but would potentially struggle generating enough of a signal to be picked up by the rear EAFR.
3) The CAM is just a Microphone. This would mean it requires either no or very little power (even Condenser Mics usually require only Milliwatts) but the signal would be very hard to send over long distances and would require the EAFR to have a preamp.
In general it is audio engineering 101 to place a preamp as close to the source as possible to avoid noise. Thus I would rule out 3. It has both ups and downs to convert the analog signal to a digital signal, and there is a possibility they'd do both. In either case I am confused from an audio engineering standpoint why the rear EAFR would not pickup audio from the CAM if the forward EAFR does. Unless the rear EAFR is fed (audio) data only via BUS, which would be an interesting choice.
Also keep in mind that historically the CVR was also located in the tail section and very much received an analog signal over the entire distance. There's really no technical reason this wouldn't be possible, I routinely use far longer cables when running audio signals at concerts and those can't use compression because it would dumpster sound quality.
So, yeah, I don't understand why there would be a mismatch between the recordings of either EAFR, unless there was something else preventing all signal transmission towards the rear EAFR. The CVR in the rear has been a thing for 80 years now.
Regards,
Justus
My understanding is that, as you say, the CAM has a preamp. That preamp can be powered by the RIPS that accompanies the forward EAFR.
In addition, I believe there is a single analogue connection from the CAM+preamp to the aft EAFR in addition to the analogue connection from the CAM+preamp to the forward EAFR. I believe, but am not sure,that the other flight-deck audio (headsets) is carried digitally over the fibre-optic network to the aft EAFR. The network may or may not be in operation in the event of an electrical failure: I simply don't know.
The publicly available information I can find is not stunningly clear about this.
AEROSAFETY WORLD, January 2008 - https://flightsafety.org/asw/jan08/a...47-48.pdf?dl=1
In the 787, the EAFRs store within their CVR-function memory partitions two hours of data from four audio channels and all data link messages. \x93The CVR function receives audio from three digital audio crew channels provided by the flight deck audio system and one analog audio channel from the cockpit area microphone and preamplifier,\x94 Elliott said.( Jim Elliott, a systems/applications engineer for the manufacturer. )
The Cockpit Voice Recorder function records the flight deck communications between crew members and also captures the general acoustical sound environment of the flight deck. The CVR function receives three analog audio crew channels provided by the Flight Deck Audio System and one analog audio channel from the cockpit Area Microphone and Preamplifier (AMP). The cockpit area audio and the three audio crew channels are recorded in both the forward and the aft installed EAFR recorders. The CVR recording duration is two hours minimum. Recorded audio can only be downloaded when the EAFR is off the aircraft.
https://data.ntsb.gov/Docket/Documen...ort-Master.PDF
Two EAFRs are installed on Boeing 787 aircraft, one forward and one aft. The forward and aft recorders are powered by the left and right 28V DC buses respectively. The forward recorder is equipped with a recorder independent power supply (RIPS) to provide backup power to the recorder for approximately 10 minutes once left DC bus power is lost. Both recorders record the same set of flight data independent of each other.
What I have been unable to determine is whether the right and/or left 28 V DC buses are powered from the main battery in case of failure of the AC power supply. To my untrained eye, it looks like the Captain's flight displays are powered from the main battery in extremis (28 V DC - C1), but that there are various circuit breakers, that could be automated, that may or may not allow or prevent other loads (such as the F/O's flight displays (28 V DC - C2), or the aft EAFR, being supplied by the main battery, (See link to diagram). There could well be very drastic automated load shedding.
https://kb.skyhightex.com/wp-content...l-1024x640.png
If the right 28 V DC bus was unpowered for any period, it follows that the aft EAFR was not recording for that period. This would make the forward EAFR important in case of a power failure that prevented the right 28 V DC bus from providing power.
All the information that is unclear to me will be transparently clear to the crash investigators. But it seems to me that the aft EAFR will not hold data for any period that the right 28 V DC bus is not operating. Whether that applies to this incident is an open question.
June 22, 2025, 17:50:00 GMT
permalink Post: 11908714
SLF here. Mods - please delete summarily if this does not contribute to the discussion, I have no wish to waste anyones time. No 'AI' was used in the preparation of this post.
My understanding is that, as you say, the CAM has a preamp. That preamp can be powered by the RIPS that accompanies the forward EAFR.
In addition, I believe there is a single analogue connection from the CAM+preamp to the aft EAFR in addition to the analogue connection from the CAM+preamp to the forward EAFR. I believe, but am not sure,that the other flight-deck audio (headsets) is carried digitally over the fibre-optic network to the aft EAFR. The network may or may not be in operation in the event of an electrical failure: I simply don't know.
The publicly available information I can find is not stunningly clear about this.
AEROSAFETY WORLD, January 2008 - https://flightsafety.org/asw/jan08/a...47-48.pdf?dl=1
GE Aviation: Consolidate and increase recording power with the 3254F EAFR. - https://www.geaerospace.com/sites/de...rder-3254F.pdf
As for power, this NTSB document describes the power set-up for the EAFRs
https://data.ntsb.gov/Docket/Documen...ort-Master.PDF
So the forward EAFR is powered from the left 28V DC bus with the possibility of being powered by the RIPS, and the aft EAFR is powered from the right 28 V DC bus.
What I have been unable to determine is whether the right and/or left 28 V DC buses are powered from the main battery in case of failure of the AC power supply. To my untrained eye, it looks like the Captain's flight displays are powered from the main battery in extremis (28 V DC - C1), but that there are various circuit breakers, that could be automated, that may or may not allow or prevent other loads (such as the F/O's flight displays (28 V DC - C2), or the aft EAFR, being supplied by the main battery, (See link to diagram). There could well be very drastic automated load shedding.
https://kb.skyhightex.com/wp-content...l-1024x640.png
If the right 28 V DC bus was unpowered for any period, it follows that the aft EAFR was not recording for that period. This would make the forward EAFR important in case of a power failure that prevented the right 28 V DC bus from providing power.
All the information that is unclear to me will be transparently clear to the crash investigators. But it seems to me that the aft EAFR will not hold data for any period that the right 28 V DC bus is not operating. Whether that applies to this incident is an open question.
My understanding is that, as you say, the CAM has a preamp. That preamp can be powered by the RIPS that accompanies the forward EAFR.
In addition, I believe there is a single analogue connection from the CAM+preamp to the aft EAFR in addition to the analogue connection from the CAM+preamp to the forward EAFR. I believe, but am not sure,that the other flight-deck audio (headsets) is carried digitally over the fibre-optic network to the aft EAFR. The network may or may not be in operation in the event of an electrical failure: I simply don't know.
The publicly available information I can find is not stunningly clear about this.
AEROSAFETY WORLD, January 2008 - https://flightsafety.org/asw/jan08/a...47-48.pdf?dl=1
GE Aviation: Consolidate and increase recording power with the 3254F EAFR. - https://www.geaerospace.com/sites/de...rder-3254F.pdf
As for power, this NTSB document describes the power set-up for the EAFRs
https://data.ntsb.gov/Docket/Documen...ort-Master.PDF
So the forward EAFR is powered from the left 28V DC bus with the possibility of being powered by the RIPS, and the aft EAFR is powered from the right 28 V DC bus.
What I have been unable to determine is whether the right and/or left 28 V DC buses are powered from the main battery in case of failure of the AC power supply. To my untrained eye, it looks like the Captain's flight displays are powered from the main battery in extremis (28 V DC - C1), but that there are various circuit breakers, that could be automated, that may or may not allow or prevent other loads (such as the F/O's flight displays (28 V DC - C2), or the aft EAFR, being supplied by the main battery, (See link to diagram). There could well be very drastic automated load shedding.
https://kb.skyhightex.com/wp-content...l-1024x640.png
If the right 28 V DC bus was unpowered for any period, it follows that the aft EAFR was not recording for that period. This would make the forward EAFR important in case of a power failure that prevented the right 28 V DC bus from providing power.
All the information that is unclear to me will be transparently clear to the crash investigators. But it seems to me that the aft EAFR will not hold data for any period that the right 28 V DC bus is not operating. Whether that applies to this incident is an open question.
Having two combined recorders is already more backup than what had previously been the norm, in addition theres the independently powered area mic going analog to the front recorder.
The common models I have checked the sheets for also provides a digital output (which is probably sent to the aft recorder via normal busses.
Having a seperate analog line going to the aft recorder would be several Kg of extra weight, and probably a substantial amount of loom design and paperwork for what is then a backup to an already redundant system.
Hence, imho why this signal only goes to the forward recorder. It is already a \xabbonus\xbb.
The power for microphone and preamp is in the >1watt range range, completely insignificant.
I am still interested in reliable information as to what is expected to be on the recorder of an aircraft which has lost the generators, what about the battery powered prinary instruments? Does some systems and the aft recorder come online with the RAT or would everything be down to the one cockpit mic? Surely not?
June 30, 2025, 21:18:00 GMT
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.
June 30, 2025, 22:04:00 GMT
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 June 2025 at 22:19 .
June 30, 2025, 22:21:00 GMT
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 June 2025 at 23:01 . Reason: Quote from a week ago; this is not a Hamsterwheel thread, thanks!
June 30, 2025, 22:49:00 GMT
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.
June 30, 2025, 23:09:00 GMT
permalink Post: 11913939
Except:
The longer this takes the more crew actions or lack thereof become the centerpiece of the investigation.
More then 1,100 787\x92s have been delivered and flying the last 14 years.
Hundreds fly every single day.
Not a whisper from any of the aviation authorities worldwide. No emergency AD\x92s..nothing.
- A \x91quick turnaround\x92 of a passenger aircraft is 2.5-3hrs
- Fuel in CDG is no doubt more expensive then at DEL. Also a crew doesn\x92t just take extra fuel without dispatchers concurring
- If anything it may have carried a little extra from DEL.
- Turnaround was 2:38 or close to it.
- Engines run on their own tank for take off. Two different tanks with the same contamination would be exceptionally rare.
- A complete electrical failure due to some massive event combined with two tanks contaminated would be akin to a lightning strike on a lottery winner.
The longer this takes the more crew actions or lack thereof become the centerpiece of the investigation.
More then 1,100 787\x92s have been delivered and flying the last 14 years.
Hundreds fly every single day.
Not a whisper from any of the aviation authorities worldwide. No emergency AD\x92s..nothing.
June 30, 2025, 23:52:00 GMT
permalink Post: 11913954
Except:
The longer this takes the more crew actions or lack thereof become the centerpiece of the investigation.
More then 1,100 787\x92s have been delivered and flying the last 14 years.
Hundreds fly every single day.
Not a whisper from any of the aviation authorities worldwide. No emergency AD\x92s..nothing.
- A \x91quick turnaround\x92 of a passenger aircraft is 2.5-3hrs
- Fuel in CDG is no doubt more expensive then at DEL. Also a crew doesn\x92t just take extra fuel without dispatchers concurring
- If anything it may have carried a little extra from DEL.
- Turnaround was 2:38 or close to it.
- Engines run on their own tank for take off. Two different tanks with the same contamination would be exceptionally rare.
- A complete electrical failure due to some massive event combined with two tanks contaminated would be akin to a lightning strike on a lottery winner.
The longer this takes the more crew actions or lack thereof become the centerpiece of the investigation.
More then 1,100 787\x92s have been delivered and flying the last 14 years.
Hundreds fly every single day.
Not a whisper from any of the aviation authorities worldwide. No emergency AD\x92s..nothing.
July 11, 2025, 23:26:00 GMT
permalink Post: 11919991
Speculations laid to rest
I am going by the list in the excellent post here:
Air India Ahmedabad accident 12th June 2025 Part 2
Anyway, here goes:
A. Misconfiguration or wrong takeoff data — OUT : 5 tons under MTOW, flaps 5, takeoff roll uneventful
B. Flaps retracted post-takeoff instead of gear — OUT : flaps 5 still set at crash
C. Low-altitude capture — OUT : throttle was at take-off thrust the whole time
D. Loss of both engines at or shortly after rotation — IN: confirmed to have occurred 3-4 seconds after liftoff
I. Bird strike/FOD — OUT
II.Fuel-related
1. Loss of electric fuel pumps — OUT
2. Fuel contamination — as good as OUT , but lab work is ongoing
3. Vapour lock — OUT
III. Improper maintenance — mostly OUT , switches might have been defective
IV. Large-scale electrical fault (e.g. due to water in E&E bay) — OUT . This would have been obvious from the flight recorder.
V. Shutdown of engines by TCMA — OUT . Conditions not met (not on ground, throttle not at idle)
VI. (Inadvertent) shutdown by flight crew
1. Spontaneous execution of memory items (fuel control switches OFF, then ON; deploy RAT) due to assumed engine malfunction — OUT from CVR
2. No indications whatsoever of an intentional shutdown for nefarious reasons — IN but unsupported
VII. Malfunction/mishandling of the fuel cutoff switches (most recent)
1. Wear or improper operation of the switches, so that they do not lock but can shift back into the OFF position. — IN
Read the previous post to this by 9 lives and reconsider VII.1
Senior Pilot
2. Spilled drink leading to short in the wiring — IN (barely) , 8 separate switch contacts must be affected in just the right way
If you never supported any of the theories that are now out, pat yourself on the back!
Anyway, here goes:
A. Misconfiguration or wrong takeoff data — OUT : 5 tons under MTOW, flaps 5, takeoff roll uneventful
B. Flaps retracted post-takeoff instead of gear — OUT : flaps 5 still set at crash
C. Low-altitude capture — OUT : throttle was at take-off thrust the whole time
D. Loss of both engines at or shortly after rotation — IN: confirmed to have occurred 3-4 seconds after liftoff
I. Bird strike/FOD — OUT
II.Fuel-related
1. Loss of electric fuel pumps — OUT
2. Fuel contamination — as good as OUT , but lab work is ongoing
3. Vapour lock — OUT
III. Improper maintenance — mostly OUT , switches might have been defective
IV. Large-scale electrical fault (e.g. due to water in E&E bay) — OUT . This would have been obvious from the flight recorder.
V. Shutdown of engines by TCMA — OUT . Conditions not met (not on ground, throttle not at idle)
VI. (Inadvertent) shutdown by flight crew
1. Spontaneous execution of memory items (fuel control switches OFF, then ON; deploy RAT) due to assumed engine malfunction — OUT from CVR
2. No indications whatsoever of an intentional shutdown for nefarious reasons — IN but unsupported
VII. Malfunction/mishandling of the fuel cutoff switches (most recent)
1. Wear or improper operation of the switches, so that they do not lock but can shift back into the OFF position. — IN
Read the previous post to this by 9 lives and reconsider VII.1
Senior Pilot
2. Spilled drink leading to short in the wiring — IN (barely) , 8 separate switch contacts must be affected in just the right way
If you never supported any of the theories that are now out, pat yourself on the back!
Last edited by Senior Pilot; 12th July 2025 at 03:40 . Reason: added comment
July 12, 2025, 01:47:00 GMT
permalink Post: 11920083
Spoiler
It seems like people are jumping to conclusions about the pilots and letting Boeing off the hook without proper investigation. Instead of providing a professional, detailed transcript of the cockpit voice recorder (CVR), we’re just getting casual comments about what the pilot allegedly said. Critical information—like the timing of transmissions, the checklist items completed before takeoff, and other key details that should be on the CVR—are essential for understanding what happened in the cockpit, especially since the crash occurred so soon after takeoff. In my view, the preliminary report feels too convenient for certain parties involved.
Examining the before-takeoff checklists seems like it would be akin to examining the re-arrangement of the deckchairs before the titanic even hit the iceberg.
The engines were switched off. Unlike Embraer, B & A have no protections stopping you switching an engine off inadvertently. From everything in the report, everything operated exactly as designed. I am not certain of how long the relight window is without windmilling speed, but +- 10 seconds seems entirely reasonable.
The outstanding question that presumably requires much more in-depth investigation of the wreckage items and CVR audio is whether:
- the cutoff switches were operated deliberately (and by who)
- the cutoff switches were operated inadvertently (and by who)
- the cutoff switches were bumped (by what) and the guards failed or weren't installed
- some electrical failure perfectly mimicked both many-pole switches being operated, then being operated again (seems unlikely)
July 12, 2025, 12:14:00 GMT
permalink Post: 11920575
Deliberate pilot action should be ruled out until any evidence and motivation for why that's the case emerges.
All we know is the fuel cut off switches were flipped to Cutoff for 10 seconds and then to run again. Not how or by what. The focus should be on how this could occur. Accidentally, technical malfunction, a foreign object somehow hitting and moving them or other reason?
Theories needs to be tested in a cockpit with the exact configuration of this aircraft and with the angles and forces involved as much as we can. It should be possible to simulate it pretty closely and whatever happened should be repeatable. It's going to be something extremely unlikely, or we'd have seen it before in 10 years of 787 service.
All we know is the fuel cut off switches were flipped to Cutoff for 10 seconds and then to run again. Not how or by what. The focus should be on how this could occur. Accidentally, technical malfunction, a foreign object somehow hitting and moving them or other reason?
Theories needs to be tested in a cockpit with the exact configuration of this aircraft and with the angles and forces involved as much as we can. It should be possible to simulate it pretty closely and whatever happened should be repeatable. It's going to be something extremely unlikely, or we'd have seen it before in 10 years of 787 service.
He didn\x92t say, \x93did you just see that pink elephant fall off the dashboard?\x94
How are you going to \x93simulate something pretty closely\x94 when it\x92s also \x93extremely unlikely\x94?
The chance that it was a mechanical or electrical failure of both fuel switches , 2 seconds apart , is for all intents and purposes, zero.
Therefore they were moved by hand.
July 12, 2025, 19:08:00 GMT
permalink Post: 11920761
Can i respectfully suggest that an electrical fault causing these issues, given the enormous straw grasping that such a speculation requires (when taking into consideration elements we do know, from both the data feed and the CVR), should also fall into the bracket outlined in the first paragraph, as the odds of such an event still point us to the second paragraph..?
On reopening we've gone straight back into incredibly implausible (in my view so implausible as to be virtually impossible) around electrical faults and the hamster wheel of "does it record the electrical or the physical state".
Given what we do know, any conclusion other than someone physically moved the switches really requires evidence at this point rather than conjecture.
July 12, 2025, 21:42:00 GMT
permalink Post: 11920857
Like I said,
if you take the preliminary report version of cockpit dialog at face value
, then if the fuel cutoff toggles were never physically turned off maybe they were not physically turned back on. Immediately prior to this flight the pilots reported a STAB master caution, which was investigated but 'no fault' was found. Intermittent electrical fault? Software/logic problem? Stranger things have happened. At least one maintenance engineer would have been in the cockpit immediately prior to this flight. The actions taken by this person(s) should also be part of the investigation.
July 12, 2025, 23:05:00 GMT
permalink Post: 11920909
If it resulted in an eicas message, then the confused conversation, leading to (several) cycling attempts to reset them successfully to RUN, those 10 seconds later doesn\x92t sound unreasonable at all to me.
Not been in that situation, obviously, but I have certainly been in stressed situations where somewhere, someone (or something) pressed the wrong button, and I need to find out which one.
10 seconds is really not a long time if it is unexpected. It is very short.
Please also remember:
-We have no idea of exactly what was said. Whether the conversation referred to a error message, engines spooling down or physical switch movement/position. Throw in possible translation inaccuracies, and we can conclude even less from the information about the conversation, or what the level of clarity or confusion were.
-There is up to 2 seconds of margin of error in the time code of events because of the (speculated) sampling rate of 1Hz.
Not been in that situation, obviously, but I have certainly been in stressed situations where somewhere, someone (or something) pressed the wrong button, and I need to find out which one.
10 seconds is really not a long time if it is unexpected. It is very short.
Please also remember:
-We have no idea of exactly what was said. Whether the conversation referred to a error message, engines spooling down or physical switch movement/position. Throw in possible translation inaccuracies, and we can conclude even less from the information about the conversation, or what the level of clarity or confusion were.
-There is up to 2 seconds of margin of error in the time code of events because of the (speculated) sampling rate of 1Hz.
I'm talking about an electrical failure (for example a short), which is already implausibly affecting both (independent) circuits, causing an issue in a circuit that as I understand it fails open anyway, then resolving itself to become functional again - incidentally in roughly the same time frame that a pilot would notice an issue and seek to correct.
This doesn't require knowledge of the cockpit conversation or judgement on speed (or otherwise) of the recovery. It's purely that an already incredibly unlikely scenario (electrical failure) becomes even more unlikely with the spontaneous *and synchronised, but not perfectly so* removal of the fault state of whatever this failure was.
*Edit* Given my previous post has been removed it would appear that the mods also misread this to do with timing of *pilots response*, which I find a little odd as it was in response to a comment about electrical failure...
To be honest at this point for me we are immediately hamster wheeling again, and this time because any commentary around either electrical circuit issues (astronomical odds) or accidental device triggering cut off (no evidence nor can there be right now) are speculation in nature and have to be. Equally, while the obvious culprit is hands on the switches, any comments about why again are speculation and have to be.
There's nothing more anyone can get to on this one until further CVR data is released in my view. Bowing out.
Last edited by Mrshed; 12th July 2025 at 23:18 .
July 12, 2025, 23:22:00 GMT
permalink Post: 11920919
Sorry you are missing my point.
I'm talking about an electrical failure (for example a short), which is already implausibly affecting both (independent) circuits, causing an issue in a circuit that as I understand it fails open anyway, then resolving itself to become functional again - incidentally in roughly the same time frame that a pilot would notice an issue and seek to correct.
This doesn't require knowledge of the cockpit conversation or judgement on speed (or otherwise) of the recovery. It's purely that an already incredibly unlikely scenario (electrical failure) becomes even more unlikely with the spontaneous *and synchronised, but not perfectly so* recovery of whatever this failure was.
I'm talking about an electrical failure (for example a short), which is already implausibly affecting both (independent) circuits, causing an issue in a circuit that as I understand it fails open anyway, then resolving itself to become functional again - incidentally in roughly the same time frame that a pilot would notice an issue and seek to correct.
This doesn't require knowledge of the cockpit conversation or judgement on speed (or otherwise) of the recovery. It's purely that an already incredibly unlikely scenario (electrical failure) becomes even more unlikely with the spontaneous *and synchronised, but not perfectly so* recovery of whatever this failure was.
I also think the time fits, sampling margins taken into accounts.
I don\x92t know what happened, but I think something in this vein of common mode failure in closely placed switches, connectors and looms, though completely dismissed by some, is in the realm of possible, and does not nearly demand the the impossible set up some claims it does.
I talk from experience with large broadcast installs, some made for posterity, some temporary, in which I would dare say the number of connectors looms and switches dwarfs any aircraft, in a fraction of the time, and I have seen some weird s***. At the same time, doesn\x92t nearly has to answer to the same life or death standards, and there is certainly a much larger number of much better paid people involved with the aircraft design.
I agree there is a bit of hamsterwheeling, especially with people thinking they know what was said on the flight deck, and about some of the systems.
But I find there has been some good points made, especially regarding human factors, interaction design, robustness of old and tried designs.
I have seen input from several experts in tangential fields that I find very interesting just in a general sense.
July 14, 2025, 00:11:00 GMT
permalink Post: 11921797
tdracer, thank you.
I have watched the nonsense posted about 'that is a bad design' as regards the fuel switches and have bitten my tongue.
It's a sane and rational design choice unless one is a default Boeing basher.
There are two sets of two switches near to each other (see the photos and figures further up) that are important (one due to fuel, one due to a primary flight control, the horizontal stab). They are protected from inadvertent movement in two different ways based on their physical proximity.
1) Stab (influencing) switches use the covered guard. (The Horizontal Stab is a primary flight control).
2) The fuel switches are stopped from casual movement by the design of that switch (which has been discussed to death) unless you pull out then them move them to the other position.
See how this works, folks who don't fly?
Stab switches: uncover, then move. Two steps.
Fuel switches: pull out, then move. Two steps.
They look different and they feel different.
Given their proximity, the designers (who have to deal with ergonomics) provided both a visual and a tactile clue that they are different, and what switch your fingers are touching or trying to move.
Will that choice guarantee that some idiot won't activate a wrong switch?
No, it won't, because you can't idiot proof everything ... the universe will always provide a bigger idiot.
But it does offer two, not one, cues to "wait, what switch am I about to activate?" for the trained user and is thus a sound design choice. Yes, pilots do undergo training for how to use all of the switches in the cockpit/flight deck.
Really.
Not kidding about this.
(Have I ever moved a wrong lever or switch? Yes).
Oh, by the way, those who have posted here who fly the 737, 757, 767, 777, and 787, have affirmed the operation and usefulness of the fuel switches. IIRC one of our 777 flyers pointed out that his captain had written up one such switch since it wasn't working right.
Yes, friends on PPRuNe, you can know how they work and if they are worn, or feel as though they are not working correctly. You can do the write up and the maintenance team can replace the switch (or fix it, or replace the quadrant, yadda yadda).
As noted by others, those switches are used on every flight.
You'll know how it should feel/work, and if it doesn't feel or work correctly you make mention of that to the engineers/maintenance crew (depending on which side of the pond you are on).
The Bulletin from several years ago does not prevent normal maintenance, and write ups, from happening on a routine basis (as with various other things on aircraft that get written up).
I had three switch design and placement factors explained to me - visual, tactile, and positional - over 40 years ago when I was going through blind cockpit checks prior to getting initially qualified in the SH-2F.
As I flew other aircraft I would notice various choices made as regards all three factors. (A fascinating sub topic of its own, but I'll stop there).
I thus say to DiffTailShim, and whatever test pilot from the UK posted his noise: no, you are wrong.
The design decision is sound.
That Embraer did/does it differently (which is cool, there is more than one way to peel an onion
) has little or nothing to do with this accident.
One could argue that their proximity might have an impact, but that would require evidence that something to do with the Stab Switches was involved in this event.
So far, that vague mention of a write up from a previous flight about a stab light gives us a tenuous thread, but not a lot to work with.
I have watched the nonsense posted about 'that is a bad design' as regards the fuel switches and have bitten my tongue.
It's a sane and rational design choice unless one is a default Boeing basher.
There are two sets of two switches near to each other (see the photos and figures further up) that are important (one due to fuel, one due to a primary flight control, the horizontal stab). They are protected from inadvertent movement in two different ways based on their physical proximity.
1) Stab (influencing) switches use the covered guard. (The Horizontal Stab is a primary flight control).
2) The fuel switches are stopped from casual movement by the design of that switch (which has been discussed to death) unless you pull out then them move them to the other position.
See how this works, folks who don't fly?
Stab switches: uncover, then move. Two steps.
Fuel switches: pull out, then move. Two steps.
They look different and they feel different.
Given their proximity, the designers (who have to deal with ergonomics) provided both a visual and a tactile clue that they are different, and what switch your fingers are touching or trying to move.
Will that choice guarantee that some idiot won't activate a wrong switch?
No, it won't, because you can't idiot proof everything ... the universe will always provide a bigger idiot.
But it does offer two, not one, cues to "wait, what switch am I about to activate?" for the trained user and is thus a sound design choice. Yes, pilots do undergo training for how to use all of the switches in the cockpit/flight deck.
Really.
Not kidding about this.
(Have I ever moved a wrong lever or switch? Yes).
Oh, by the way, those who have posted here who fly the 737, 757, 767, 777, and 787, have affirmed the operation and usefulness of the fuel switches. IIRC one of our 777 flyers pointed out that his captain had written up one such switch since it wasn't working right.
Yes, friends on PPRuNe, you can know how they work and if they are worn, or feel as though they are not working correctly. You can do the write up and the maintenance team can replace the switch (or fix it, or replace the quadrant, yadda yadda).
As noted by others, those switches are used on every flight.
You'll know how it should feel/work, and if it doesn't feel or work correctly you make mention of that to the engineers/maintenance crew (depending on which side of the pond you are on).
The Bulletin from several years ago does not prevent normal maintenance, and write ups, from happening on a routine basis (as with various other things on aircraft that get written up).
I had three switch design and placement factors explained to me - visual, tactile, and positional - over 40 years ago when I was going through blind cockpit checks prior to getting initially qualified in the SH-2F.
Spoiler
I thus say to DiffTailShim, and whatever test pilot from the UK posted his noise: no, you are wrong.
The design decision is sound.
That Embraer did/does it differently (which is cool, there is more than one way to peel an onion
) has little or nothing to do with this accident.
One could argue that their proximity might have an impact, but that would require evidence that something to do with the Stab Switches was involved in this event.
So far, that vague mention of a write up from a previous flight about a stab light gives us a tenuous thread, but not a lot to work with.
Last edited by Lonewolf_50; 14th July 2025 at 00:37 .
July 15, 2025, 15:46:00 GMT
permalink Post: 11923037
I'm suggesting that occasionally electrics or electronics can do strange things as happened in 2015 with the loss of the A400m after an update had accidentally wiped some important software out.
One of my instructors landed a Baron without its undercarriage after an electrical fault in spite of cranking the gear down by hand and having it retract.
At the moment there isn't a plausible cause besides insanity.
One of my instructors landed a Baron without its undercarriage after an electrical fault in spite of cranking the gear down by hand and having it retract.
At the moment there isn't a plausible cause besides insanity.