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Someone Somewhere
July 01, 2025, 10:19:00 GMT permalink Post: 11914164 |
Not really relevant to what you quoted though, as the scenario in question requires:
I also don't see any evidence that engine driven fuel pumps alone must be able to handle this scenario: provide enough fuel flow for takeoff and climb, even while the pitch is rotating, even in a hot environment with significant weight, even while the gear is stuck down.
I know that the engine driven pumps have documented limitations and that the regulations allow for some limitations. I know that at least one of these limitation is high altitude and I _suspect_ that the design intends for this unlikely scenario (engine driven fuel pumps alone with no AC pumps) to guarantee enough fuel flow to get to an airport and land. I also suspect that the APU is expected to solve loss of all AC generators - and as we know, there wasn't enough time for it to start in this scenario. The limitations at high altitude are primarily air/volatiles degassing out of the fuel. That's not going to be much of an issue at sea level, even if the engines are a bit higher up during rotation. APU is a nice-to-have; it's on the MEL. If you lose all four generators, it's because of some major carnage in the electrical software/hardware and chances of putting the APU on line even if it's operating are very slim. |
Someone Somewhere
July 01, 2025, 10:42:00 GMT permalink Post: 11914172 |
One of the things I've learned on this thread is that planes landing with the RAT deployed may be rare, but it does happen. The videos I've watched suggest that the engines were usually running as the plane landed, but of course the RAT can't be un-deployed in flight.
My question is: what caused the RAT to deploy on those flights? Presumably reports have to be submitted in those cases? ASN has a section on electrical power incidents: https://asn.flightsafety.org/asndb/cat/ACSE In particular try these: https://assets.publishing.service.go...009_G-EZAC.pdf https://asn.flightsafety.org/wikibase/233343 https://asn.flightsafety.org/wikibase/219748 https://asn.flightsafety.org/wikibase/34357 |
EDML
July 01, 2025, 11:38:00 GMT permalink Post: 11914210 |
This is my latest attempt to square the circle using all the data points and minimal assumptions. The main shortcoming of the analysis is not knowing the maximum L/D and the speed for maximum LD with the gear down, flaps 5, and the RAT extended. However, if I use a reasonable number in my opinion for the L/D in that configuration and assume that the airplane is being flown at the speed for it, it will not get to the crash site. The distance from the runway of the crash site is from a previous graphic (1.55 km); the rotation point from fdr, permalink 314; 200 feet max height above the runway being generally accepted; crash site 50 feet below the runway elevation cited previously. An average speed of 180 knots is consistent with the dimensions given and 30 seconds flight time. A flare at 50 feet will briefly increase the L/D to 20, maybe even 30 (500 feet more than shown) but still not enough to make up the shortfall, In fact, with a head wind the L/D will be lower than assumed as well as if the speed being flown is higher or lower than required for maximum L/D in that configuration. In other words, there must have been some thrust available.
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nachtmusak
July 01, 2025, 12:06:00 GMT permalink Post: 11914222 |
This is my latest attempt to square the circle using all the data points and minimal assumptions. The main shortcoming of the analysis is not knowing the maximum L/D and the speed for maximum LD with the gear down, flaps 5, and the RAT extended. However, if I use a reasonable number in my opinion for the L/D in that configuration and assume that the airplane is being flown at the speed for it, it will not get to the crash site. The distance from the runway of the crash site is from a previous graphic (1.55 km); the rotation point from fdr, permalink 314; 200 feet max height above the runway being generally accepted; crash site 50 feet below the runway elevation cited previously. An average speed of 180 knots is consistent with the dimensions given and 30 seconds flight time. A flare at 50 feet will briefly increase the L/D to 20, maybe even 30 (500 feet more than shown) but still not enough to make up the shortfall, In fact, with a head wind the L/D will be lower than assumed as well as if the speed being flown is higher or lower than required for maximum L/D in that configuration. In other words, there must have been some thrust available.
![]() As the aircraft visibly continues to climb past that height (and for a longer period than ADS-B data covers, if the camera's perspective casts doubt on that), it seems rather clear to me that it reached its peak height past the end of the runway. In light of this I find the fact that people keep calculating a glide from the runway to the crash site to be a bit strange. Wouldn't the first step of any math be to try to determine where it started descending? |
Tailspin Turtle
July 01, 2025, 13:05:00 GMT permalink Post: 11914261 |
There is easily-correctable available data with the aircraft's altitude at pretty much the end of the runway and it is not at 200 feet (it's around 100\xb112.5 feet).
As the aircraft visibly continues to climb past that height (and for a longer period than ADS-B data covers, if the camera's perspective casts doubt on that), it seems rather clear to me that it reached its peak height past the end of the runway. In light of this I find the fact that people keep calculating a glide from the runway to the crash site to be a bit strange. Wouldn't the first step of any math be to try to determine where it started descending? |
adfad
July 01, 2025, 13:36:00 GMT permalink Post: 11914278 |
Thrust is non-linear and complex. Reaction engines (i.e. fans, props) are generally most efficient at minimum power - lowest excess velocity. Turbine engines are generally most efficient at high power. These cancel out somewhere in the middle. With two engines at low power, you also don't have the drag from the dead engine or the drag from the rudder countering yaw.
Cavitating destroys pumps rapidly - someone upthread said replacing the fuel pump immediately is SOP if it has suction fed. Expect end of life in tens of hours rather than tens of thousands. Some aircraft have switched to using jet/venturi pumps powered by returned fuel, like the A220. The electric boost pumps there are mainly for redundancy and are shut down in cruise; only one in each wing tank. Some A320s replace the centre override pumps with venturi transfer pumps. My question is then: what is the minimum loss of thrust in both engines (perhaps more relevantly expressed as a % in fuel flow reduction from expected) that could produce the profile we saw. I appreciate this is a figure with many variables including timing and rate of loss. The reason I think this question is relevant is because we pretty much have 2 prevailing theories at this point:
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jdaley
July 01, 2025, 14:04:00 GMT permalink Post: 11914293 |
The cctv neither confirms nor denies that top of climb could be as high as 270'. My 1km/200' estimate was conservative. I guessed 160kt average over the 7s to allow for the 25007 wind and some deceleration. Basically you cannot rule out loss of thrust around the time of loss of electrics. |
SloppyJoe
July 09, 2025, 12:45:00 GMT permalink Post: 11918371 |
Firstly, it's not rapid cycling of the fuel control switches, you turn them off then back on and see if it starts, this can take more than a minute as you have to wait to see if the action was successful. Second problem as mentioned above, the speed was far too low for a successful relight, you would most likely end up with a hot start or no start, most likely with a lot of smoke out the back due to unburnt fuel.
edited to add, after reading about the 787 it seems it uses electrical power to start. Same sort of issue though if not enough power, which is likely given the RAT was out. Last edited by SloppyJoe; 9th July 2025 at 12:57 . |
AerocatS2A
July 10, 2025, 01:30:00 GMT permalink Post: 11918727 |
I don't have any comment on it other than to note that the manual is not specific to Air India. My B787-9 FCTM is identical as far as I can tell. The actual memory item for dual failure is to reset the fuel switches and start the RAT. It is also conditional on the engines being sub idle as noted by the other poster.
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MaybeItIs
July 10, 2025, 01:41:00 GMT permalink Post: 11918730 |
I don't have any comment on it other than to note that the manual is not specific to Air India. My B787-9 FCTM is identical as far as I can tell. The actual memory item for dual failure is to reset the fuel switches and start the RAT. It is also conditional on the engines being sub idle as noted by the other poster.
* (Or to be fair, these guys, this cockpit team were...) Last edited by MaybeItIs; 10th July 2025 at 01:55 . Reason: grammar (still bad, never mind), a bit better 2nd time |
Magplug
July 10, 2025, 08:59:00 GMT permalink Post: 11918849 |
A couple of points if I may......
I don't see it written in the 787 FCOM but I have always been told that the action of resetting the Engine Cutoff switches in the event of a dual engine failure, is merely backing up what the FADECs have already done. If there is an 'engine event' the FADECs will manage ignition and fuel-flow to restore the thrust that was demanded before the event. If that management has failed then the manual resetting may be more successful. (The same holds true for the RAT, manual selection is merely backing up the auto-deployment). Any airline pilot will tell you that executing an in-flight relight on a big engine, no matter if it is by electric start, windmilling RPM or cross-bleed assisted, can take between 1 and 3 minutes to restore power. This aircraft was airborne for less that 30 seconds. No pilot in his right mind would prioritise an in-flight relight procedure, in a situation where they had neither the time, the height nor the speed for it to succeed. I have no doubt the crew focussed entirely on pointing the aircraft at the clearest area they could see, to mitigate what would inevitably follow. |
adfad
July 10, 2025, 13:18:00 GMT permalink Post: 11919024 |
The data recorder has all the information most are questioning. They already know if the fuel control switches were selected to cutoff and they know if this happened before or after the loss of thrust. Perhaps the sequence of events will be more clear tomorrow. I can tell you that from aircraft rotation to loss of thrust was a very short time period. Perhaps 8 seconds. I simply won’t believe in that time period the crew were taking any non deliberate actions that would have shut the motors down.
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KSINGH
July 11, 2025, 20:40:00 GMT permalink Post: 11919771 |
- fuel cut offs were found in the RUN position
- on take off roll both engines lost power as the fuel cut offs went from RUN to cutoff - CVR recorded one pilot asking why they had gone to CUTOFF - within 10 seconds the fuel cutoff was moved back to RUN -RAT was deployed, APU had begun auto start - 32 seconds after Vr the MAYDAY was called This should also dispel a lot of the comments about AAIB-India, Indian culture in general and general competence. For a preliminary report this is far more thorough and extensive than what would normally be expected and they\x92ve kept Boeing, GE, FAA and investigators from US, UK, Canada and Portugal in the loop from the start They have also clarified why it took so long to do the EAFR download- because of the extensive damage they had to source specialist equipment from the NTSB that only arrived on the 23rd of June (they downloaded on the 24th) so all that talk of a \x91coverup\x92 is pretty embarrassing now of course the big question is why/how those switches were commanded into cutoff in the first place the exact sequence at Vr is the most critical, there hasn\x92t been much scrutiny at all that I can see in the Indian/international media of the personal background of the flight deck crew which has happened in other suspected pilot initiated disasters in the past, I guess this is an avenue investigators will have been doing themselves |
Engineless
July 11, 2025, 20:40:00 GMT permalink Post: 11919772 |
The aircraft achieved the maximum recorded airspeed of 180 Knots IAS at about 08:08:42
UTC and immediately thereafter, the Engine 1 and Engine 2 fuel cutoff switches transitioned from RUN to CUTOFF position one after another with a time gap of 01 sec. The Engine N1 and N2 began to decrease from their take-off values as the fuel supply to the engines was cut off. In the cockpit voice recording, one of the pilots is heard asking the other why did he cutoff. The other pilot responded that he did not do so. The CCTV footage obtained from the airport showed Ram Air Turbine (RAT) getting deployed during the initial climb immediately after lift-off (fig. 15). No significant bird activity is observed in the vicinity of the flight path. The aircraft started to lose altitude before crossing the airport perimeter wall. As per the EAFR, the Engine 1 fuel cutoff switch transitioned from CUTOFF to RUN at about 08:08:52 UTC. The APU Inlet Door began opening at about 08:08:54 UTC, consistent with the APU Auto Start logic. Thereafter at 08:08:56 UTC the Engine 2 fuel cutoff switch also transitions from CUTOFF to RUN. When fuel control switches are moved from CUTOFF to RUN while the aircraft is inflight, each engines full authority dual engine control (FADEC) automatically manages a relight and thrust recovery sequence of ignition and fuel introduction. The EGT was observed to be rising for both engines indicating relight. Engine 1’s core deceleration stopped, reversed and started to progress to recovery. Engine 2 was able to relight but could not arrest core speed deceleration and re-introduced fuel repeatedly to increase core speed acceleration and recovery. The EAFR recording stopped at 08:09:11 UTC As per the EAFR data both engines N2 values passed below minimum idle speed, and the RAT hydraulic pump began supplying hydraulic power at about 08:08:47 UTC. RAT in extended position 15 As per the EAFR, the Engine 1 fuel cutoff switch transitioned from CUTOFF to RUN at about 08:08:52 UTC. The APU Inlet Door began opening at about 08:08:54 UTC, consistent with the APU Auto Start logic. Thereafter at 08:08:56 UTC the Engine 2 fuel cutoff switch also transitions from CUTOFF to RUN. When fuel control switches are moved from CUTOFF to RUN while the aircraft is inflight, each engines full authority dual engine control (FADEC) automatically manages a relight and thrust recovery sequence of ignition and fuel introduction. The EGT was observed to be rising for both engines indicating relight. Engine 1’s core deceleration stopped, reversed and started to progress to recovery. Engine 2 was able to relight but could not arrest core speed deceleration and re-introduced fuel repeatedly to increase core speed acceleration and recovery. The EAFR recording stopped at 08:09:11 UTC At about 08:09:05 UTC, one of the pilots transmitted “MAYDAY MAYDAY MAYDAY”. 08:08:42 Engine 1 and Engine 2 fuel cutoff switches transitioned from RUN to CUTOFF position. One of the pilots asks the other why did he cutoff. The other pilot responded that he did not do so. 08:08:52 Engine 1 fuel cutoff switch transitioned from CUTOFF to RUN 08:08:56 Engine 2 fuel cutoff switch also transitions from CUTOFF to RUN Who (or what?) operated the cutoff switches? Last edited by Engineless; 11th July 2025 at 20:53 . |
DTA
July 11, 2025, 20:56:00 GMT permalink Post: 11919785 |
This part of the report shows how early the RAT was out.
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Musician
July 11, 2025, 22:09:00 GMT permalink Post: 11919886 |
Seconds count:
As per the EAFR, the Engine 1 fuel cutoff switch transitioned from CUTOFF to RUN at about
08:08:52 UTC. The APU Inlet Door began opening at about 08:08:54 UTC, consistent with the APU Auto Start logic. Thereafter at 08:08:56 UTC the Engine 2 fuel cutoff switch also transitions from CUTOFF to RUN. When fuel control switches are moved from CUTOFF to RUN while the aircraft is inflight, each engines full authority dual engine control (FADEC) automatically manages a relight and thrust recovery sequence of ignition and fuel introduction. The EGT was observed to be rising for both engines indicating relight.
Engine 1's core deceleration stopped, reversed and started to progress to recovery.
Engine 2 was able to relight but could not arrest core speed deceleration and re-introduced fuel repeatedly to increase core speed acceleration and recovery. The EAFR recording stopped at 08:09:11 UTC.
That was with 10 seconds delay vs. 13 seconds for engine 2.
Time was spent with the verbal exchange, and then perhaps each pilot expected the other to put the switch back? Anyway, the preliminary report also establishes that the aircraft had only 3-4 seconds of powered flight. (Would the gear lever be operated that early?) Everyone who saw that from the CCTV video, pat yourselves on the back. ![]() Mayday call, dual engine failure, RAT deployment all confirmed. TCMA was a red herring, the aircraft was firmly in air mode as the accident unfolded, and the thrust levers were at takeoff thrust the whole time. |
Seamless
July 11, 2025, 22:12:00 GMT permalink Post: 11919889 |
Spoiler
I wouldn't put too much significance in the "01 second" since this still is close enough for an unintentional cause. No matter what: The design and position of the fuel cut off switches is potentially prone for mishaps. |
9 lives
July 11, 2025, 23:25:00 GMT permalink Post: 11919990 |
There is mention of fire damage or thermal damage to the centre pedestal, perhaps enough to identify the position of the switches but not to be able to determine their internal physical state relating to the detent mechanisms.
For myself, I have total confidence that the switches functioned as intended. Obviously they commanded the fuel valve as intended, and can be seen intact (other than the plastic caps), and in the run position, so it is safe to conclude that a mechanical/electrical fault of both independent switches at the same moment is unlikely in the extreme. The FDR data states that they were moved to "off" position, which caused the engine shutdown, then returned to "run", so they obviously were mechanically and electrically functional. The automatic deployment of the RAT is an indicator of the airplane systems sensing an engine shutdown, as is the APU autostart. Pax 11A mentioned the green cabin lights, which, if I understand correctly is an indication of a complete electrical generation failure.The time of all these events can be plotted from recorded data, which I expect we'll see in a full report later. In the mean time, it all makes unfortunate sense. |
Musician
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! ![]() Last edited by Senior Pilot; 12th July 2025 at 03:40 . Reason: added comment |
physicus
July 12, 2025, 00:08:00 GMT permalink Post: 11920029 |
Timeline of known events with source attribution from the preliminary report:
08:07:33 ATC: Takeoff clearance 08:07:37 A-SMGCS: Aircraft starts rolling 08:08:33 EAFR: V1 153kts 08:08:35 EAFR: Vr 155kts 08:08:39 EAFR: Gnd-Air mode transition 08:08:42 EAFR: Max IAS 180kts, Eng 1/2 Cutoff switches activate within 1 second of each other 08:08:42 CVR: "Why did you cut off", "I did not" (exact time not specified) 08:08:42 A-SMGCS: RAT deployed (exact time not specified) 08:08:47 EAFR: Both engine N2 below min idle. RAT hyd pwr commences 08:08:52 EAFR: Eng 1 cutoff to RUN 08:08:54 EAFR: APU inlet door opens (auto start logic) 08:08:56 EAFR: Eng 2 cutoff to RUN 08:09:05 ATC: Mayday call 08:09:11 EAFR recording stops Fuel cutoff switches operated within 1 second of each other suggests to me that the locking mechanism wasn't working as per (SAIB) No. NM-18-33. Any loose item could have accidentally (or not) operated the switches (including hands). Last edited by physicus; 12th July 2025 at 00:24 . |
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