June 20, 2025, 10:26:00 GMT
permalink Post: 11906808
... the gear, as far as I can establish (not openly published according to Google), weighs around 8-odd to 10 tonnes. Typically, retracts in about 10 seconds. I estimate it's no more than a 2 metre lift. As far as I can work out (using 3m to make the value higher), that requires about 30kW (rough estimate, budgetary figure, not accounting for it being a curved path, so it's probably higher closer to fully up), but whether wind pressure affects it, I have no idea. Anyway, 30kW isn't a huge (additional) load on a 225kVA alternator. Less than I'd imagined.
Now I'm wondering how big (power ratings) the hydraulic pump and motor are? No doubt, they're driven by a VSD. Can anyone comment, please?
Now I'm wondering how big (power ratings) the hydraulic pump and motor are? No doubt, they're driven by a VSD. Can anyone comment, please?
As for hydraulic pumps, they are limited to how much flow they can produce. The pressure drops significantly during large control movements and the landing gear actuators in particular need a large flow to keep them moving.
When all pumps are operating, engine driven or otherwise that pressure drop is limited, when down to just one small RAT driven pump there's only so much it can do and the design ensures that control of the aircraft can be maintained on just RAT power.
There won't be enough power from the RAT generator to power emergency aircraft systems and large hydraulic pumps. This is why it has its own small hydraulic pump.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Generators/Alternators Hydraulic Failure (All) RAT (All)
June 20, 2025, 22:58:00 GMT
permalink Post: 11907384
Thanks for the response!
Yes that's why I phrased it that way, but keep in mind the Eastern L1011 that lost all three engines for exactly this reason.
Of course that was some time ago and regulations and hardware have changed, but asking because the odds maybe miniscule, but it has happened.
Yes that's why I phrased it that way, but keep in mind the Eastern L1011 that lost all three engines for exactly this reason.
Of course that was some time ago and regulations and hardware have changed, but asking because the odds maybe miniscule, but it has happened.
Critical similar systems will not be touched by the same engineer/mechanic. EG. Engine oil servicing. In fact only one critical system should be tampered with between flights.
The Airline's ETOPS Manual lists these vital critical systems.
Subjects: None
June 20, 2025, 23:34:00 GMT
permalink Post: 11907392
This has been mentioned several times.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Electrical Failure Fuel (All) Fuel Cutoff
June 21, 2025, 08:13:00 GMT
permalink Post: 11907564
Wouldn't "fail safe open" imply that the valves would open on loss of control signals or power. They don't. They stay just where they were before loss of power or control signal. If I understood tdracer's description of the HPSOV it can only be open or closed. That's not true of the spar valves which are motor driven and can stop in any intermediate position if power is lost.
The only way this is relevant to the accident is if the shut off valves had been commanded closed and then power had been lost. The valves would not open.
The only way this is relevant to the accident is if the shut off valves had been commanded closed and then power had been lost. The valves would not open.
What I mean is that with engines running, fuel shut off valve(S) open, if there is a loss of electrical power the valves will remain open.
This is standard design on all the gas turbine engines I have worked on.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Fuel (All) Fuel Cutoff High Pressure Shutoff Valve Spar Valves
June 21, 2025, 15:12:00 GMT
permalink Post: 11907831
There are maintenance access doors directly belew the APU that open up like a Clamshell.
There are other access doors nearby for example just forward of the APU firewall bulkhead there is an access door, this allows entry into the stabiliser bay rear section.
There is another stab bay access door just forward of the horizontal stabiliser on the left side which allows access to the forward stabiliser area, screw jack, fin access and the rear pressure bulkhead.
I don't think there are any others.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): APU
June 22, 2025, 11:22:00 GMT
permalink Post: 11908458
Re, water in fuel tanks.
For a significant amount to build up, either the scavenge system hasn't been working properly and/or the weekly water drain checks have been omitted.
Tens of gallons will not build up on a couple of humid days of operations.
I have only once come across an aircraft that had significant water in the main tanks. That was during the winter months when the drain valves would freeze. So, to overcome this the aircraft needed significant down time to allow the fuel to warm up. As you can imagine for the sake of a quiet life and to meet operational requirements occasionally these water drain checks would be missed now and again. The trouble with that is if they are missed for several weeks, we can have a problem. One airline I used to handle only did the water drain checks when the aircraft had a daily check at main base. This aircraft often had the Daily checks done away from base. Hence water drain checks never got done unless specifically scheduled.
I do not think the Air India aircraft would have this problem in the summer months.
For a significant amount to build up, either the scavenge system hasn't been working properly and/or the weekly water drain checks have been omitted.
Tens of gallons will not build up on a couple of humid days of operations.
I have only once come across an aircraft that had significant water in the main tanks. That was during the winter months when the drain valves would freeze. So, to overcome this the aircraft needed significant down time to allow the fuel to warm up. As you can imagine for the sake of a quiet life and to meet operational requirements occasionally these water drain checks would be missed now and again. The trouble with that is if they are missed for several weeks, we can have a problem. One airline I used to handle only did the water drain checks when the aircraft had a daily check at main base. This aircraft often had the Daily checks done away from base. Hence water drain checks never got done unless specifically scheduled.
I do not think the Air India aircraft would have this problem in the summer months.
Subjects: None
June 22, 2025, 11:27:00 GMT
permalink Post: 11908463
I like the theory introduced by
TryingToLearn
where a short in the BTB in a few milliseconds puts so much load on the HP rotor that it reduces its rpm until it suffocates. However, isn\x92t it that even with the BTB welded into a solid piece of copper that each generator can still shed all load through its own GCU/GPC almost instantly on sensing the short? Wouldn\x92t this scenario then also require at least one GCU per engine to fail as well?
Also generator drive shafts are designed to shear under heavy load to stop them damaging the gearbox and 'stopping' the engine core shaft from running.
https://www.amtechinternational.com/...t/quill-shaft/
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Generators/Alternators
June 22, 2025, 19:34:00 GMT
permalink Post: 11908784
Interesting and informative post from JustusW on 2025-06-21@ 1704 on the ins and outs of various implementations of digital logic (SW, FPGAs, ASICs) and how it has changed and is changing.
I am using my usual approach to trying to figure out what happened in this accident. Which is to perform a possibility analysis: ideally, to consider all possible scenarios and prune out ones that do not fit with the facts as we know them. Might sound easy but it's not trivial, and there aren't that many people who become really good at it (and I am not even sure that my colleagues who are good at it think that I am......).
Severe reduction of thrust, simultaneously, just after unstick is one of the "facts as we know them". The control systerns for engines and fuel systems on the 787 are based on digital-logical electronics, including SW. Every digital-logical system may have bugs. In forty years of working with and around such systems I have never encountered one which didn't. Never. (Some eminent colleagues did try to do so with the "Tokeneer" project - and it took a year or two to find the bugs).
A bug in the digital-logical FADEC is a possibility. As far as I am concerned, it stays in the possibility analysis until it can be ruled out. Which it cannot be at this stage.
For this purpose, it does not matter what the logic is based on, or whether some SW-HW architectures can be less susceptible, for whatever reasons, than others.
I am using my usual approach to trying to figure out what happened in this accident. Which is to perform a possibility analysis: ideally, to consider all possible scenarios and prune out ones that do not fit with the facts as we know them. Might sound easy but it's not trivial, and there aren't that many people who become really good at it (and I am not even sure that my colleagues who are good at it think that I am......).
Severe reduction of thrust, simultaneously, just after unstick is one of the "facts as we know them". The control systerns for engines and fuel systems on the 787 are based on digital-logical electronics, including SW. Every digital-logical system may have bugs. In forty years of working with and around such systems I have never encountered one which didn't. Never. (Some eminent colleagues did try to do so with the "Tokeneer" project - and it took a year or two to find the bugs).
A bug in the digital-logical FADEC is a possibility. As far as I am concerned, it stays in the possibility analysis until it can be ruled out. Which it cannot be at this stage.
For this purpose, it does not matter what the logic is based on, or whether some SW-HW architectures can be less susceptible, for whatever reasons, than others.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): FADEC
June 29, 2025, 09:22:00 GMT
permalink Post: 11912902
Ask the Apollo astronauts? The ISS Crew members? But don't mention 9/11! The fireballs just don't compare.
It has been said that there are three stages of truth: ridicule, violent opposition and acceptance as self-evident. Obviously, we're not there yet
Of course the aircrew needs a lav within their easy reach. I don't have a cross section or plan to work with (Google not obliging), but if you post, I'll take a look. Likely, I'd compartmentalize the lav with the EE Bay space immediately below, and install a "bilge tray and drain" below the lav space and above the EE Bay compartment. If it has to be used for EE Bay gear, I'd probably rack the 28V Batteries there, with the required fireproof casings and exhaust ports etc. (Also absurd, but true.) And I'd make sure the batteries themselves were fully protected by moulded plastic "hats", similar to what they use on the big 12V battery pairs on large trucks. I guess you could fit a couple of TRUs there as well, again, well-protected from dripping conductive liquids... And maybe, you could house [one of?] the EE Bay air conditioner unit
there? But none of the flight-critical board racks or other sensitive electronic equipment. Any moisture-related faults there would be just too random and difficult to pin down.
It has been said that there are three stages of truth: ridicule, violent opposition and acceptance as self-evident. Obviously, we're not there yet
Of course the aircrew needs a lav within their easy reach. I don't have a cross section or plan to work with (Google not obliging), but if you post, I'll take a look. Likely, I'd compartmentalize the lav with the EE Bay space immediately below, and install a "bilge tray and drain" below the lav space and above the EE Bay compartment. If it has to be used for EE Bay gear, I'd probably rack the 28V Batteries there, with the required fireproof casings and exhaust ports etc. (Also absurd, but true.) And I'd make sure the batteries themselves were fully protected by moulded plastic "hats", similar to what they use on the big 12V battery pairs on large trucks. I guess you could fit a couple of TRUs there as well, again, well-protected from dripping conductive liquids... And maybe, you could house [one of?] the EE Bay air conditioner unit
It will come as no surprise to anyone that EE bays are well protected with the sort of things you have described.
The 787 batteries are also in separate EE bays. Main one in the front and the dedicated APU battery in the power electrics bay aft of the landing gear.
They are both contained in fireproof boxes that will vent to atmosphere in the event of a thermal runaway.
I have been working on 787s for over a decade and leaks from gallies and lavs has not once been on my list of snags.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): APU
June 29, 2025, 10:48:00 GMT
permalink Post: 11912945
Can anyone suggest a good reason why the captain should issue a Mayday call at that point? The crew should have been extremely busy with the situation. Aviate, Navigate, Communicate is a mantra we are all familiar with. So why communicate?
Having discussed the accident with experienced pilot colleagues, we have all considered that the Egyptair 990 case offered similarities. Yet this is almost a taboo subject.
And one's suspicions are raised by the fact that Air India/Tata are keeping ICAO out of the post-crash investigation.
Incidentally, I sincerely hope that we are wrong about the possibility of a deliberate dual engine shutdown shortly after rotation.
Having discussed the accident with experienced pilot colleagues, we have all considered that the Egyptair 990 case offered similarities. Yet this is almost a taboo subject.
And one's suspicions are raised by the fact that Air India/Tata are keeping ICAO out of the post-crash investigation.
Incidentally, I sincerely hope that we are wrong about the possibility of a deliberate dual engine shutdown shortly after rotation.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Dual Engine Failure Engine Failure (All) Engine Shutdown ICAO MAYDAY
June 29, 2025, 10:57:00 GMT
permalink Post: 11912953
Didn't I just say that?
"with the required fireproof casings and exhaust ports etc."
Ok, didn't mention thermal runaway, but that's the purpose of the fireproof boxes and exhaust ports. But the whole risk/ danger of thermal runaway is another issue, isn't it? There are safer batteries that are not lead-acid whales. Are the any other planes out there that need fireproof boxes and vent pipes to contain and purge burning battery fumes etc to the outside? It's not just the fumes that are the issue, of course.
Good to hear, hope you know them inside out and catch every issue. Please keep an eye out for trickles down walls in the EE Bays though.
Good to hear, hope you know them inside out and catch every issue. Please keep an eye out for trickles down walls in the EE Bays though.
The 787 being of CFRP construction and using an entirely different air conditioning system that mitigates the problem does not seem to suffer from excess condensation
Subjects: None
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.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Electrical Failure Fuel (All)
July 01, 2025, 00:40:00 GMT
permalink Post: 11913970
I did look into this while analyzing the audio for RAT confirmation, but I did not conclude with anything other than that the engines where clearly not at any kind of take off power.
I did not find good enough material to compare to, and time was lacking a bit.
There is engine noise, or engine-like noise from there, somewhat comparable to an engine at idle, that fades out into the background noise at the same rate as the RAT. I don\x92t know if it comes from an engine at idle, windmilling, an engine producing some power, or if it is even just aerodynamic noise from the rest of the airframe.
I\x92ll give it another go if time allows.
I did not find good enough material to compare to, and time was lacking a bit.
There is engine noise, or engine-like noise from there, somewhat comparable to an engine at idle, that fades out into the background noise at the same rate as the RAT. I don\x92t know if it comes from an engine at idle, windmilling, an engine producing some power, or if it is even just aerodynamic noise from the rest of the airframe.
I\x92ll give it another go if time allows.
APU autostart? Not sure really, it takes several seconds for the inlet door to open.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): APU RAT (All)
July 01, 2025, 08:49:00 GMT
permalink Post: 11914118
In my experience the APU supplies enough power to run all systems. Hydraulic pumps, fuel pumps etc
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): APU Fuel (All) Hydraulic Failure (All)
July 10, 2025, 09:36:00 GMT
permalink Post: 11918879
[emphasis added]
D Bru : if that were actually the scenario, would they not instead be focusing on why "for some extraordinary reason [they were] confronted with both engines out on lift off", rather than having "narrowed its focus to the movement of the plane's fuel control switches", which would just be a side effect not a root cause?
But this is starting to devolve into a hamster wheel again.
D Bru : if that were actually the scenario, would they not instead be focusing on why "for some extraordinary reason [they were] confronted with both engines out on lift off", rather than having "narrowed its focus to the movement of the plane's fuel control switches", which would just be a side effect not a root cause?
But this is starting to devolve into a hamster wheel again.
Anyway, the other thread is open at the moment, maybe this should be moved there.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Fuel (All) Fuel Cutoff Switches
July 10, 2025, 16:30:00 GMT
permalink Post: 11919130
With the recent (albeit unofficial)
indications that both engine fuel control switches were found in the CUTOFF position
, I wonder if it's time to reassess the tone and meaning of Captain Sabharwal's final transmission (perhaps translated from Hindi) \x93Thrust not achieved\x85 falling\x85 Mayday! Mayday! Mayday!\x94
Viewed in light of the reported switch positions, the phrasing feels increasingly ambiguous. As is often stated on PPRunE, communication comes after aviation so you wonder why in the crisis and at low altitude, this message was transmitted. Being so atypical, the message merits re-examination.
Viewed in light of the reported switch positions, the phrasing feels increasingly ambiguous. As is often stated on PPRunE, communication comes after aviation so you wonder why in the crisis and at low altitude, this message was transmitted. Being so atypical, the message merits re-examination.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Fuel (All) Fuel Cutoff Switches MAYDAY RUN/CUTOFF
July 12, 2025, 08:37:00 GMT
permalink Post: 11920352
I cannot imagine a situation where any pilot would be moving a crew bag within seconds of getting airborne.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Fuel (All) Fuel Cutoff Fuel Cutoff Switches Fuel Cutoff Switches (detent)
July 13, 2025, 17:02:00 GMT
permalink Post: 11921451
If the guards to the stab trim switches were left open by maintenance, I could see a situation in which muscle memory might lead to closing the adjacent fuel control switches. This would also explain the "I didn't do it response", as he believed he was merely closing the guards instead.
When trouble shooting, it normally resets through a BITE test. I don't remember ever having to touch the stab cut off switches as part of line trouble shooting. The aircraft is on a turnaround, if the test doesn't clear the message further trouble shooting may be lengthy, most airlines would want the aircraft dispatched in accordance with the MEL.
Deactivating the relevant transducer involves entering the stab bay, disconnecting a plug and writing up the deferral.
If it's true, as someone above suggested, that the aircraft was signed off an hour before departure, that is not last minute by the way, then I would guess that the BITE test cleared the message.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Fuel (All) Fuel Cutoff Switches MEL Muscle Memory Switch Guards
July 13, 2025, 20:43:00 GMT
permalink Post: 11921632
Incidentally, the APU door started opening *after* the initiation of relight of the first engine.
Without the APU, would there have been sufficient power to restart even one engine, never mind two?
Could this be why the delay between the first and second switches being moved to RUN?
Does it also mean that in reality the 10 seconds between OFF and RUN is immaterial as there was insufficient electrical power to start the engines anyway?
Without the APU, would there have been sufficient power to restart even one engine, never mind two?
Could this be why the delay between the first and second switches being moved to RUN?
Does it also mean that in reality the 10 seconds between OFF and RUN is immaterial as there was insufficient electrical power to start the engines anyway?
Normal start uses a lot of electrical power to drive the two starters. In a situation with only the RAT supplying electrical power there won't be anywhere near enough power to turn even one starter. Restart relies on windmilling only. Igniters don't need a huge amount of power, fuel will be gravity fed to the engine driven pumps. The APU autostart function will use power from the dedicated APU battery only.
Edit to add, it can take an age for the APU to start off the battery. Well over a minute.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): APU RAT (All) RUN/CUTOFF Relight
July 15, 2025, 19:42:00 GMT
permalink Post: 11923211
SLF, so (p)prune if necessary.
What I'm wondering, knowing that all electrical systems in aircrafts are designed with redundancy and separation in mind, what about the grounding of these circuits? Is there a common ground, or do all switches have separate wires back to their own power source?
Assuming the fuel control (and other) switches are make-contacts, and there is a common ground, that could cause issues. I have no idea what the work on the STAB cutout switches issues entailed but if any physical work was done in that area of the console, that might cause issues if there is a common ground.
I know what grounding issues can do, I've been a Citroen XM driver.
What I'm wondering, knowing that all electrical systems in aircrafts are designed with redundancy and separation in mind, what about the grounding of these circuits? Is there a common ground, or do all switches have separate wires back to their own power source?
Assuming the fuel control (and other) switches are make-contacts, and there is a common ground, that could cause issues. I have no idea what the work on the STAB cutout switches issues entailed but if any physical work was done in that area of the console, that might cause issues if there is a common ground.
I know what grounding issues can do, I've been a Citroen XM driver.
The Stab Trim (Posn) Xdcr fault reported on the previous sector is very common on this type. Trouble shooting does not involve touching those switches or digging around the wires under the panel.
Last edited by TURIN; 17th July 2025 at 11:57 .
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Fuel (All) Fuel Cutoff Switches