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Shep69
June 20, 2025, 21:52:00 GMT permalink Post: 11907348 |
To be clear, are you stating categorically or guessing (or neither, and I'm misreading you and you mean something else) that the 787's autothrottle will come
out of HOLD
and into SPD mode
below 400 feet
by design in response to the altitude that's set in the mode control panel, entirely by itself, without the autopilot engaged? Not that this is the way it would behave in normal flight - that this is the way it is
designed
to behave while it's in HOLD mode for takeoff?
I am actually looking for an answer from a pilot (or at least someone with an FCOM who can share any relevant passages) because nothing I have been able to look up on my own suggests that this is the case. All secondary sources I can find just say that the autothrottle is inhibited under 400 feet on takeoff, with my impression being that the crew is expected to manage thrust manually during that phase of flight. The incidents I was able to turn up involving an aircraft attempting to capture a target altitude at takeoff specifically don't help either: - G-ECOE: Flight was completely normal until the crew engaged the autopilot at 1350 feet, at which point the aircraft started diving to the target of 0 feet. However it involved a Dash 8 and not only is that not a Boeing aircraft, it doesn't have an autothrottle to begin with. Nothing to conclude from this. - F-WWKH: Again automated deviation was triggered by the crew engaging the autopilot a few seconds after takeoff as part of a test flight. However again also not a Boeing aircraft (an A330) and the selected target altitude was 2000 feet so the autopilot tried to pitch up to capture it. Not sure if anything can be concluded from this. - A6-EQI: The most relevant, being a Boeing 777, with wide speculation being that the selected altitude was left at 0 feet. However the preliminary report is very thin so there's little to go on in the way of factual information, but the problem seems to entirely have been that the pilot flying was following the flight directors without question. There's zero indication of any loss of thrust, in fact they seem to have nearly entered an overspeed condition partly due to the shallow climb angle implying that the engines were doing just fine. So it doesn't seem like the selected altitude caused the autothrottle to do anything. I am sorry if it seems like I'm banging on about this autothrottle point a bit much but as an engineer it just seems completely backwards to me. What exactly is the point of the HOLD mode or of setting those specific gates (80 knots, 400 feet) if the autothrottle can so easily come out of it? The design might as well not have it at all and just leave the autothrottle in THR REF for takeoff then - what would be the difference? I am guessing because although I flew the 777 I never tried a low altitude capture before VNAV engaged — and it`s been a few years). But think it probably would. As one goes through 50’ LNAV engages; VNAV is normally armed prior to the EFIS check if it`s to be used (which it usually is). So in this scenario LNAV would have been engaged but since VNAV is armed but never engages my guess is that the automatics would engage in SPD/LVAV/ALT. I could be wrong. The PF would have been hand flying (and obviously not following the flight director with autothrottles engaged). HOLD is present in many other regimes of flight; all it means is that the auththrottle (right now) is not controlling the throttles and they stay where they are—and the PF can move them if desired at will. Fr` instance, when descending in FLCH or even VNAV SPD the throttles will usually be in HOLD. (To me this usually meant `hold` the throttles—and tweek them in descent as required). Thrust can be modulated to adjust rate of descent (the throttles become vertical speed levers). On altitude capture in the case of FLCH or path capture in the case of VNAV SPD (in descent) the auththrottles kick in and it becomes SPD/xxx/ALT (or VPTH or VALT as the case might be). Most everyone knew the autothrottles would not engage below 400` and that FLCH in descent at very low altitudes was not an appropriate mode — and they did not activate providing low speed protection in the case of Asiana. IIRC our throttles went into HOLD at 60 knots and stayed there until VNAV activated (THR REF—takeoff thrust). It was also possible that the autothrottles under some environmentals wouldn`t fully achieve takeoff thrust setting (EPR or N1 depending on which engines) and they could be manually moved in HOLD to achieve it. Although I don`t remember that as ever happening. But at this point it`s a guess because I never did it (MCP set at low altitude on takeoff with VNAV never engaging). Perhaps someone else has. Last edited by Shep69; 20th June 2025 at 22:05 . |
nachtmusak
June 20, 2025, 22:24:00 GMT permalink Post: 11907362 |
The autopilot would NOT be engaged below 400\x92 (or 200\x92 in the 78\x96although I doubt anyone engages it that low). The autopilot and autothrottles are separate systems but do interact. The autothrottles typically WOULD be engaged from the start of the takeoff roll; using the TOGA levers to set takeoff thrust).
I am guessing because although I flew the 777 I never tried a low altitude capture before VNAV engaged \x97 and it`s been a few years). But think it probably would. As one goes through 50\x92 LNAV engages; VNAV is normally armed prior to the EFIS check if it`s to be used (which it usually is). So in this scenario LNAV would have been engaged but since VNAV is armed but never engages my guess is that the automatics would engage in SPD/LVAV/ALT. I could be wrong. The PF would have been hand flying (and obviously not following the flight director with autothrottles engaged. HOLD is present in many other regimes of flight; all it means is that the auththrottle (right now) is not controlling the throttles and they stay where they are\x97and the PF can move them if desired at will. Fr` instance, when descending in FLCH or even VNAV SPD the throttles will usually be in HOLD. (To me this usually meant `hold` the throttles\x97and tweek them in descent as required). Thrust can be modulated to adjust rate of descent (the throttles become vertical speed levers). On altitude capture in the case of FLCH or path capture in the case of VNAV SPD (in descent) the auththrottles kick in and it becomes SPD/xxx/ALT (or VPTH or VALT as the case might be). Most everyone knew the autothrottles would not engage below 400` and that FLCH in descent at very low altitudes was not an appropriate mode \x97 and they did not activate providing low speed protection in the case of Asiana. But at this point it`s a guess because I never did it (MCP set at low altitude on takeoff with VNAV never engaging). Perhaps someone else has. Also to be clear I do know that the autopilot and autothrottle are independent - I have been talking about the autopilot because as I listed, in the incidents I could find where the aircraft automatically tried to capture a target altitude on takeoff, the autopilot was first engaged. So my impression was that until then the aircraft might provide guidance (like in the Emirates case) but will not actually do anything to change the thrust, pitch, etc parameters that have been set. |
M.Mouse
June 20, 2025, 22:29:00 GMT permalink Post: 11907367 |
he autopilot would NOT be engaged below 400’ (or 200’ in the 78–although I doubt anyone engages it that low. The autopilot and autothrottles are separate systems but do interact. The autothrottles typically WOULD be engaged from the start of the takeoff roll; using the TOGA levers to set takeoff thrust).
I am guessing because although I flew the 777 I never tried a low altitude capture before VNAV engaged — and it`s been a few years). But think it probably would. As one goes through 50’ LNAV engages; VNAV is normally armed prior to the EFIS check if it`s to be used (which it usually is). So in this scenario LNAV would have been engaged but since VNAV is armed but never engages my guess is that the automatics would engage in SPD/LVAV/ALT.
HOLD is present in many other regimes of flight; all it means is that the auththrottle (right now) is not controlling the throttles and they stay where they are—and the PF can move them if desired at will. Fr` instance, when descending in FLCH or even VNAV SPD the throttles will usually be in HOLD. (To me this usually meant `hold` the throttles—and tweek them in descent as required). Thrust can be modulated to adjust rate of descent (the throttles become vertical speed levers). On altitude capture in the case of FLCH or path capture in the case of VNAV SPD (in descent) the auththrottles kick in and it becomes SPD/xxx/ALT (or VPTH or VALT as the case might be).
Most everyone knew the autothrottles would not engage below 400` and that FLCH in descent at very low altitudes was not an appropriate mode — and they did not activate providing low speed protection in the case of Asiana.
Since the Asiana accident many airlines prohibit use of FLCH below 1,000' and the lowest altitude setting when using FLCH is then, of course, 1.000'
IIRC our throttles went into HOLD at 60 knots and stayed there until VNAV activated (THR REF—takeoff thrust). It was also possible that the autothrottles under some environmentals wouldn`t fully achieve takeoff thrust setting (EPR or N1 depending on which engines) and they could be manually moved in HOLD to achieve it. Although I don`t remember that as ever happening.
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GroundedSpanner
June 21, 2025, 15:24:00 GMT permalink Post: 11907841 |
Resubmitting following some Mod Feedback and a significant re-write. Yes, it is speculative
I have a theory that I'd like to share. It brings together various pieces of known information, along with 30+ years of my experience as an aircraft engineer that forms a plausible (IMO) explanation of what may have happened. We Know - From the Video's and the ADSB Data: That up to and for the first few seconds after take-off appears relatively normal. The AC appears to lose thrust without e.g. birdstrike or other spectacular smoke /fire producing event. That the RAT deployed. That the pilot reported 'Thrust not achieved' [Edit - We dont 'know' this - it is heavily reported] We can see that the AC had a relatively busy schedule in the few days prior to the accident flight, so there was no significant downtime for maintenance activities that could have caused incident. The AC flew DEL-CDG on 11 Jun with quite a racy turnaround in CDG of 1h12m. The centre tank would have been empty at CDG on arrival, and would have been partially filled for the return CDG-DEL. CDG-DEL Arrived 01:47 am IST. Again the Centre Tank would have been empty. But quite a bit of fuel in the wings. 8 Hrs later, at 09:48 am IST the AC departed DEL-AMD. For such a short-hop, Fuel upload would have been minimal, merely a 'topping up' if at all. Certainly nothing into the Centre Tank. DEL That night was fairly hot and humid - 57% at 02:30, 54% at 05:30, 44% at 08:30. That wing tank fuel could have picked up a fair amount of water. The flight DEL-AMD would have only used the wing pumps. Thus any water in that 'overnight' fuel would have been vigorously stirred and evenly suspended. At concentrations that would cause no ill-effect at all. The AC was on the ground at AMD for 2 Hrs, from 11:17am to 1:17 pm IST. The AC would have re-fuelled, first filling up the wing tanks to the top, then filling the centre-tank to whatever quantity necessary. There was enough time for water in the wing tanks to settle out. The B787 Fuel system has pumps in the wing tanks, and pumps in the centre tanks. The Centre Tank pumps are also known as 'override' pumps because they output a higher pressure than the wing tank pumps, thus ensuring that with all pumps running, the centre tank fuel is used first. Should the centre tank pumps stop, due to either filure or running out of fuel to pump, the wing tank pumps then produce the pressure. In the event that all pumps stop running (e.g. an electrical failure), the engines will suck the fuel from the wing tanks. The 'sucked' fuel comes from a dedicated pipe in each tank through the 'Suction Feed Check Valve' (so that pumped fuel doesn't just exit through the suction tube). The suction tube pickup is in a slightly different position to the wing pump pickups. It is conceivable to me that the suction tube pickup could have been immersed in water, settled out from the fuel in the wing tanks. Then - at start-up of the aircraft in AMD, The engines would have been supplied with fuel from the centre tank. Fresh Fuel. All OK. Wing pumps running and doing not much. But, I speculate, the suction pick-ups immersed in water. Waiting. Start up and taxi out was all normal. Runway acceleration up to v1 appears normal. V1 - Rotate - (positive rate - Gear up? - Not my debate). But somewhere around that time, I speculate that a significant electrical failure occurred. Enough for the RAT to deploy. Enough for the fuel pumps to stop. I'll not speculate on the cause. We know that it can occur, that's why the RAT was designed to operate. The engines at that point were at TOGA thrust. In a significant electrical failure, the engines will keep on doing what they were last told. Keep that thrust stable. So the AC climbed for a few seconds more. The pilots did what they were trained to do for a power failure, manage that, thankfully the engines were still going well... But there was only so much 'good' fuel in the lines. The engines sucking fuel themselves, the fuel would now be coming from the suction pickups, a different supply. A supply likely heavily water contaminated. It would take a few seconds for that contaminated fuel to actually reach the engines, but when that contaminated fuel hit, Thrust would have been significantly reduced. The EEC's would have been doing their best to maintain the thrust, firewalling the throttles would probably have little effect at that exact moment. The engines would have likely worked through that bad fuel in a shortish period of time, but a period of time that our crew did not have. A fully loaded aircraft producing less than take-off thrust, is not sustaining enough thrust for continued flight. The rest - is down to the skill of the crew in deciding exactly where to hit the ground within the very narrow range of choice they had. Last edited by GroundedSpanner; 21st June 2025 at 17:52 . Reason: Thrust not achieved comment is not proven. |
violator
June 21, 2025, 15:42:00 GMT permalink Post: 11907854 |
Resubmitting following some Mod Feedback and a significant re-write. Yes, it is speculative
I have a theory that I'd like to share. It brings together various pieces of known information, along with 30+ years of my experience as an aircraft engineer that forms a plausible (IMO) explanation of what may have happened. We Know - From the Video's and the ADSB Data: That up to and for the first few seconds after take-off appears relatively normal. The AC appears to lose thrust without e.g. birdstrike or other spectacular smoke /fire producing event. That the RAT deployed. That the pilot reported 'Thrust not achieved' We can see that the AC had a relatively busy schedule in the few days prior to the accident flight, so there was no significant downtime for maintenance activities that could have caused incident. The AC flew DEL-CDG on 11 Jun with quite a racy turnaround in CDG of 1h12m. The centre tank would have been empty at CDG on arrival, and would have been partially filled for the return CDG-DEL. CDG-DEL Arrived 01:47 am IST. Again the Centre Tank would have been empty. But quite a bit of fuel in the wings. 8 Hrs later, at 09:48 am IST the AC departed DEL-AMD. For such a short-hop, Fuel upload would have been minimal, merely a 'topping up' if at all. Certainly nothing into the Centre Tank. DEL That night was fairly hot and humid - 57% at 02:30, 54% at 05:30, 44% at 08:30. That wing tank fuel could have picked up a fair amount of water. The flight DEL-AMD would have only used the wing pumps. Thus any water in that 'overnight' fuel would have been vigorously stirred and evenly suspended. At concentrations that would cause no ill-effect at all. The AC was on the ground at AMD for 2 Hrs, from 11:17am to 1:17 pm IST. The AC would have re-fuelled, first filling up the wing tanks to the top, then filling the centre-tank to whatever quantity necessary. There was enough time for water in the wing tanks to settle out. The B787 Fuel system has pumps in the wing tanks, and pumps in the centre tanks. The Centre Tank pumps are also known as 'override' pumps because they output a higher pressure than the wing tank pumps, thus ensuring that with all pumps running, the centre tank fuel is used first. Should the centre tank pumps stop, due to either filure or running out of fuel to pump, the wing tank pumps then produce the pressure. In the event that all pumps stop running (e.g. an electrical failure), the engines will suck the fuel from the wing tanks. The 'sucked' fuel comes from a dedicated pipe in each tank through the 'Suction Feed Check Valve' (so that pumped fuel doesn't just exit through the suction tube). The suction tube pickup is in a slightly different position to the wing pump pickups. It is conceivable to me that the suction tube pickup could have been immersed in water, settled out from the fuel in the wing tanks. Then - at start-up of the aircraft in AMD, The engines would have been supplied with fuel from the centre tank. Fresh Fuel. All OK. Wing pumps running and doing not much. But, I speculate, the suction pick-ups immersed in water. Waiting. Start up and taxi out was all normal. Runway acceleration up to v1 appears normal. V1 - Rotate - (positive rate - Gear up? - Not my debate). But somewhere around that time, I speculate that a significant electrical failure occurred. Enough for the RAT to deploy. Enough for the fuel pumps to stop. I'll not speculate on the cause. We know that it can occur, that's why the RAT was designed to operate. The engines at that point were at TOGA thrust. In a significant electrical failure, the engines will keep on doing what they were last told. Keep that thrust stable. So the AC climbed for a few seconds more. The pilots did what they were trained to do for a power failure, manage that, thankfully the engines were still going well... But there was only so much 'good' fuel in the lines. The engines sucking fuel themselves, the fuel would now be coming from the suction pickups, a different supply. A supply likely heavily water contaminated. It would take a few seconds for that contaminated fuel to actually reach the engines, but when that contaminated fuel hit, Thrust would have been significantly reduced. The EEC's would have been doing their best to maintain the thrust, firewalling the throttles would probably have little effect at that exact moment. The engines would have likely worked through that bad fuel in a shortish period of time, but a period of time that our crew did not have. A fully loaded aircraft producing less than take-off thrust, is not sustaining enough thrust for continued flight. The rest - is down to the skill of the crew in deciding exactly where to hit the ground within the very narrow range of choice they had. |
lighttwin2
June 21, 2025, 15:46:00 GMT permalink Post: 11907858 |
TCMA continues to be one of the few (very unlikely) causes of/contributors to simultaneous shutdown of both engines. So far, though, I don't think we've seen a credible scenario explaining the possibility that TCMA was triggered in this accident. I'm not sure I understand your speculation.
In the scenario you are considering, it's clear that the air/ground state would be wrongly "understood" by the TCMA function. But we don't have, AFAIK , a credible theory for how that might happen. Surely it would have to result from either incorrect signals from the relevant sensors or a failure of the related logic in the FADEC TCMA function, or a combination of those. Indeed, I don't think we yet know exactly which sensor readings that logic depends on or how those readings are fed to the FADEC. Does your speculation include any thoughts about this? Also, the FADEC TCMA function has to "believe" that the engine is operating at high power and not responding to thrust lever operation. In your proposed scenario, is this also a logic failure — in both FADECs? Or false inputs from both TLs? Or are both engines actually operating at higher than commanded power levels? Or do I misunderstand your post?
Q: Would the a/c have enough kinetic energy a 184kts to climb to 100-150ft agl and then reach its final position if the engines had failed at, or just, before rotation? A: Theoretically possible - see calculation here . NB, the a/c actually flew 1.5km from the end of the runway and 2.3km from the likely point of rotation. Q: Doesn't the forward position of the gear mean that power failed after the pilots had selected gear up? A: Inconclusive - had hydraulic power had been lost prior to rotation, the gear could also be in this position - explanation here Q: If the throttle levers were brought to idle during take-off, would the A/C have applied autobrake, reversers and speedbrake? A: Yes, although there is a built in delay before reverser and speedbrake actually deploy - see here . Q: Is the ADS-B data consistent with this scenario? A: Yes, e.g. the Flightradar data shows the aircraft decelerating rapidly (12 knots in 4.2 seconds) from close to rotation. However, it's not clear how accurate this data is. For one, the altitude data is +/- 25 feet, second, while I was under the impression FR would have received airspeed data from the a/c sensors, this post suggests maybe not. Q: Does TCMA activation require the thrust levers to be at idle or does it function when the thrust levels are above idle, but where the actual thrust is above that commanded? A: No, the latter is true (i.e. idle is not required) - confirmed here - there are of course many protections against false activation Q. Did AI171 have the same software version / logic paths as NH-985 A. Unknown. That a/c had Trent 1000s so to some extent the software is different, but we understand the TCMA logic is broadly the same regardless of engine. I have not seen a post clarifying whether the TCMA software has been updated /changed via SB since 2019 to account for this incident. Be grateful if posters could refrain from speculative responses "e.g. I think this is unlikely because I feel x". I am not opining on how likely this sequence of events is, simply trying to summarise whether or not this theory has been ruled in or out. I also recommend this post for a summary to read before posting. . Last edited by lighttwin2; 21st June 2025 at 16:13 . |
skwdenyer
June 30, 2025, 14:04:00 GMT permalink Post: 11913652 |
Posters may like to read this old (2016) pprune thread on 787 engine failure procedures:
787 engine failure procedure
Some interesting comments about how a combination of ATM and derate can lead to some pretty surprisingly poor outcomes, coupled with Boeing advice not to advance thrust levers or engage TOGA. (edited for poor spelling) Last edited by skwdenyer; 30th June 2025 at 14:40 . |
Capn Bloggs
June 30, 2025, 16:26:00 GMT permalink Post: 11913745 |
Richard Godfrey has completely ignored that fact that the speed was reducing all the way down the descent. He has hypothesised a steady descent angle at around 3.5:1 and therefore concluded that one engine had stopped and the other was on ~10,000lb of thrust because, at the initial speed they needed that thrust to counter the drag. But the AOA clearly increases markedly as the aircraft approaches the ground, which means that the speed was reducing significantly.
As for statements such as:
One Engine Inoperative (OEI) just before take-off(Assumption).
​​​​​​​The Take-Off Speed at rotation is estimated at 160 KIAS (167 KTAS, 170 GS), which is higher than normal and expected in an assumed OEI take-off.
​​​​​​​The rotation point requires a runway ground roll of 2,540 m, which is longer than normal due to an assumed OEI take-off.
​​​​​​​The climb gradient is estimated at 5.09%, which is slightly above the normal range of 3% to 4%at TOGA for a Boeing 787-8, but within limits
​​​​​​​True airspeed was under-indicated due to low density, in other words the aircraft was moving faster through the air than the airspeed indicator showed, because there were fewer air molecules hitting the pitot tube in the hot, thin air
​​​​​​​The aircraft peaked early, then levelled off and started descending while passing over obstacles. It barely cleared Obstacle B by ~50 feet, which is tight, but sufficient. This explains the visibly profile in video and supports the notion of degraded climb due to hot/high conditions, heavyweight, and limited thrust margin
In a nutshell, he's saying they had an engine failure before rotation, then got all the way up to 300-odd feet (following what looked to me like an initially standard low-angle/flat 787 takeoff, then ran out of puff and crashed with the other engine running at 15-18% Thrust. Pure speculation aka WAG. |
GroundedSpanner
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. |
FullWings
July 09, 2025, 21:50:00 GMT permalink Post: 11918657 |
Propellerhead
You are correct, a low level altitude capture would back off the throttles as the FMA goes into ALT. However the FD would drop unexpectedly as would the engine noise as the throttles rolled back..... So in what world would that prompt you to call for the dual engine failure checklist rather than firewalling the throttles? This was discussed about 75 pages ago.... It makes good reading
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double-oscar
July 13, 2025, 14:45:00 GMT permalink Post: 11921364 |
It would have been useful if more of the CVR data had been released so as to see the crew interaction. Also the language used on what was released seems to refer to a third person.
However, from an operator perspective. Captain PM, FO PF. PF selects TOGA and follows the thrust levers, Captain confirms Thrust Set and replaces FO hands on the Thrust Levers. 80Kt call by PM, acknowledged by PF. Aircraft calls V1, Captain should withdraw hands from Thrust Levers and calls Rotate at Vr. PM is looking for confirmation the aircraft is climbing and calls Positive Rate. PF confirms and calls Gear Up. At this point the PF will be looking through the HUD looking to follow the flight director, the PM would be checking LNAV had engaged and at 400\x92 checking THR REF and VNAV SPD. However, at this point a loss of thrust occurred. So how was this apparent to the PF who would have been looking out with both hands on the control wheel. Reduction in pitch? GPWS call-out? Decreasing N1 on the engine instruments? EICAS ENG SHUTDOWN? What did the PM see? Who called out the situation? Were any actions called for? At some point as the generators went off line all the FO instruments would have blanked. Did the Captain assume control? I don\x92t think I would have been thinking about the Fuel Cut-Off switches at that point, yet they were specifically mentioned which does mean the switches were moved and it wasn\x92t some internal fault. Hopefully, as the CVR is further analysed some more information will come to light. |
Contact Approach
July 13, 2025, 18:03:00 GMT permalink Post: 11921494 |
It would have been useful if more of the CVR data had been released so as to see the crew interaction. Also the language used on what was released seems to refer to a third person.
However, from an operator perspective. Captain PM, FO PF. PF selects TOGA and follows the thrust levers, Captain confirms Thrust Set and replaces FO hands on the Thrust Levers. 80Kt call by PM, acknowledged by PF. Aircraft calls V1, Captain should withdraw hands from Thrust Levers and calls Rotate at Vr. PM is looking for confirmation the aircraft is climbing and calls Positive Rate. PF confirms and calls Gear Up. At this point the PF will be looking through the HUD looking to follow the flight director, the PM would be checking LNAV had engaged and at 400\x92 checking THR REF and VNAV SPD. However, at this point a loss of thrust occurred. So how was this apparent to the PF who would have been looking out with both hands on the control wheel. Reduction in pitch? GPWS call-out? Decreasing N1 on the engine instruments? EICAS ENG SHUTDOWN? What did the PM see? Who called out the situation? Were any actions called for? At some point as the generators went off line all the FO instruments would have blanked. Did the Captain assume control? I don\x92t think I would have been thinking about the Fuel Cut-Off switches at that point, yet they were specifically mentioned which does mean the switches were moved and it wasn\x92t some internal fault. Hopefully, as the CVR is further analysed some more information will come to light. Interestingly ENG 1 was cut off first\x85 |
DavidncRobson
July 14, 2025, 03:32:00 GMT permalink Post: 11921837 |
Thrust Recovery Time from Idle Condition
Originally Posted by
Mrshed
The question is what impact was had on attempts to recover the aircraft by the (presumed) lack of most or all electrical power. Response from BrogulT: From the point that the fuel cutoffs were switched back to run, the primary (perhaps only) relevant issues were time and altitude. The left engine was relit and recovering on it's own but the right would probably have needed cranking as it appears to have had a hung start because it was spooled down too far and the airspeed was too low. However, I'm pretty sure that even if the APU had already been running at takeoff, they still would have needed at least another 30 seconds if not longer for full thrust. Also, there was nowhere near enough time for the APU to start and come online here. Your claim that at least 30 seconds were needed to achieve full thrust prompted me to look up reports on the Airbus A320 crash at Habsheim in France in 1988 where the aircraft had been flown at low altitude at the minimum allowable speed and was unable to achieve sufficient thrust to ascend above a copse of trees. The extract below shows that from Idle to 83% N1 took 5 seconds after the initiation of a TOGA, so I think your estimate of 30 seconds is probably too high. However, after reading that report, I am of the opinion that AI 171 had no chance of recovering. If the FCS switches had been set to Run within 5 seconds of being set to Cut Off, there might just have been a chance, but it is not at all certain. (From Aviation Safety Network Sunday 26 June 1988) The aircraft took off from nearby Basle-Mulhouse Airport at 14:41 and climbed to 1000 feet agl. The crew started the descent three minutes later and Habsheim was in sight at 450 feet agl. The Pilot Monitoring informed the Pilot Flying that the aircraft was reaching 100 feet at 14:45:14. The descent continued to 50 feet 8 seconds later and further to 30-35 feet. Go-around power was added at 14:45:35. The A320 continued and touched trees approximately 60 meters from the end of runway 34R at 14:45:40 with a 14 degree pitch attitude and engines at 83% N1. The plane sank slowly into the forest and a fire broke out. PROBABLE CAUSES: "The Commission believes that the accident resulted from the combination of the following conditions: 1) very low flyover height, lower than surrounding obstacles; 2) speed very slow and reducing to reach maximum possible angle of attack; 3) engine speed at flight idle; 4) late application of go-around power. This combination led to impact of the aircraft with the trees. The Commission believes that if the descent below 100 feet was not deliberate, it may have resulted from failure to take proper account of the visual and aural information intended to give the height of the aircraft." |
BrogulT
July 14, 2025, 04:36:00 GMT permalink Post: 11921851 |
The extract below shows that from Idle to 83% N1 took 5 seconds after the initiation of a TOGA, so I think your estimate of 30 seconds is probably too high. However, after reading that report, I am of the opinion that AI 171 had no chance of recovering. If the FCS switches had been set to Run within 5 seconds of being set to Cut Off, there might just have been a chance, but it is not at all certain.
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EDML
July 14, 2025, 12:17:00 GMT permalink Post: 11922151 |
Even if the engine would have accelerated to TOGA - no way to fly you out of that situation being near stall speed far below Vmca, with no altitude to trade for speed on one engine.
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JustusW
July 15, 2025, 17:49:00 GMT permalink Post: 11923123 |
The STAB cutout switches are located next to the Fuel cutoff switches. What did Air India\x92s on duty AME do as part of their troubleshooting? Were panels removed to gain access to the rear of the switches and wiring? What about wiring and data connections elsewhere? What may have been disconnected/disturbed as part of this process? It would not be the first time that an engineer had innocently done something that later caused an accident. And I haven't read anything about possible nefarious action by a (disgruntled?) engineer - but I've seen lots of accusations directed at the pilot(s)...
Wires or wiring is mentioned twice in the report:
The wiring from the TO/GA switches and autothrottle disconnect switches were visible, but heavily damaged.
The aft EAFR was located on the roof top of Building A on 13th June 2025. The EAFR had impact and thermal damages to the housing. The wires were protruding from the housing and the connectors were burnt.
![]() While severely burnt the switches are still solidly in place and anything that was lodged in the switch housing itself would likely still be there. And I guess it would also be unlikely for FOD to equally impact both switches. I think I just talked myself out of the FOD theory. I find option C to be at least a productive train of thought because it may provide methods of mitigation. That is after all what we're trying to achieve in discussing this kind of accident. I would expect or at least look positively on a suggestion to use the Embraer model for operating the cutoff valves. While it introduces a secondary element that may fail, requiring the Throttle Control Levers to be at idle just seems like a good idea. How is this handled by Airbus? |
Musician
July 16, 2025, 07:06:00 GMT permalink Post: 11923473 |
So what are the odds for "crash by brain fart"? for example, when a cargo pilot inadvertantly hits TOGA on descent and then plows the aircraft into the marsh compensating?
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Lonewolf_50
July 16, 2025, 17:13:00 GMT permalink Post: 11923863 |
From the information so far available, the ones on the accident aircraft was not installed the wrong way, else the conclusion that they were in the RUN position would not be there. You don't have a theory, you don't have a hypothesis, you have an (as yet) unsupported assertion. Now, if a friend of your who works at Air India has sent you a text message, or spoken to you, and advised you privately that someone at that company had installed those switches improperly on that aircraft, then perhaps you can forward that info to the accident investigators (in whatever non attribution method you can figure out). Further that point: had the installation been faulty, or presented evidence of that, that fact would have been in the report because they found the switches intact (albeit somewhat worse off due to the post crash fire). See page 10 of the prelim, figure 13:
The thrust lever quadrant sustained significant thermal damage. Both thrust levers were found near the aft (idle) position. However, the EAFR data revealed that the thrust levers remained forward (takeoff thrust) until the impact. Both fuel control switch were found in the “RUN” position. (fig.13) The reverser levers were bent but were in the “stowed” position. The wiring from the TO/GA switches and autothrottle disconnect switches were visible, but heavily damaged"
But I'll throw you a bone: since I don't think that they have completed 100% all of their digging into the maintenance side of this, someone may turn up something odd before they issue a subsequent report, or the final report. Beyond that, thank you for your concise response to my overly long post. ![]() Last edited by Lonewolf_50; 16th July 2025 at 17:50 . |
OhForSure
July 17, 2025, 02:22:00 GMT permalink Post: 11924096 |
I have not posted on here in many years, but I feel compelled to do so now. I am a current 787 pilot and I have previously flown most Boeing types and an Airbus too. I also have an extensive background and qualifications in human factors, training and assessment. Before anybody reads any further, perhaps acquaint yourself with the notion of Occam's razor. That is, the simplest explanation is the most likely explanation. I was certain that after the preliminary report was released the preposterous conspiracy theories would finally cease, but no! It's 2025 and humans can no longer help themselves. In my opinion the captain committed suicide here. Simple.
To those suggesting an electrical phantom turned the fuel control switches off without them moving: no. Ask yourselves this: what made one pilot (PF and F/O in my opinion) ask the other "why did you cut off?" Firstly, some context. The 787 fuel control switches make a VERY distinct metallic *CLICK* sound as they are operated. EVERY 787 pilot knows it and won't forget it. It is audible even at high thrust settings owing to the 787's exceptionally quiet engines and cockpit. After rotation the pilot flying is fixated on the HUD; rotating towards the TOGA reference line (~12 degrees pitch attitude) and putting the flight path vector over the flight guidance cue. One hand would be on the control column and the other on the thrust levers. Alternatively he could have had both hands on the control column. In either scenario, the pilot flying's (again, my opinion the F/O's) inboard arm would block his peripheral view (he's focused on the HUD, remember) of the center pedestal and the fuel control switches. HE WOULD NOT SEE THE PM TURN THE FUEL CONTROL SWITCHES OFF. Ipso facto. We know the F/O was PF from the report. If the F/O stopped flying the aircraft and reached down to move the FCS from cutoff to run the captain would've plainly seen the whole thing. I can't imagine "why did you cutoff?" would be his words of choice! More like "WTF ARE YOU DOING?!?" More to the point, if the PF (F/O) did stop flying and reach down to cut one engine off, the captain would have had time to either stop him flicking the second FCS off or at least quickly flick them both back to run and potentially save the day. This plainly did not happen. So it was almost certainly the PM (Capt) that moved the fuel control switches. So what would make the PF ask the PM "why did you cut off?" if he couldn't see it happen? You would never assume with a loss of thrust that the switches had been turned off. Never. It's not a procedure. It's not a thing. Bird strike? Sure. Fuel Contam? Maybe. But the point is, in the heat of battle at 150 odd feet, you'd never jump to the conclusion that the fuel control switches were off. Never. So what triggered the PF asking the PM why he cutoff? Because he HEARD the fuel control switches move from run to cutoff, that is why. He heard those distinctive *CLICK* sounds (and yes, you can easily flick them both in less than a second FWIW) followed by the engines immediately rolling back. He would then have looked down at the switches and noticed they were in cutoff. The point to be made here is that the switches were moved by the captain. They made their distinct sound. There were no phantoms. They cannot move on their own. They didn't simultaneously fail. This drew the PF's attention away from flying and triggered the question "why did you cutoff"? Inadvertent selection of the wrong switches? No. The PM was a training captain with thousands of hours experience on the jet. I asked one of our most experienced examiners how many times he'd seen that done. The answer was "zero". Even the stab switches next to them. They're red, guarded and are of a completely different shape and operation. Gear or flap? Come on. I think we're starting to stretch things a bit now. EVEN IF it was inadvertent switching. The INSTANT you'd made that error, you'd go "oh whoops", and flick them back to run. I know startle... I teach it. This is different. You don't flick the fuel control switches off, hear the engines roll back and sit there wondering what happened for 10 seconds AFTER THE F/O JUST ASKED YOU IF YOU CUTOFF! You did something that had an instant effect on the flight. The report indicates that "why did you cutoff" was asked just after both engines rolled back. But it took another 10 seconds to flick the FCS' back to run. If it was inadvertent, the instant the other pilot called out your error you'd correct it. The report makes it clear that there was 10 seconds between that happening. 10 seconds is a LIFETIME in that situation. The training captain knew what he was doing. He only switched the FCS' back to run once he knew it was moot. So, why did he respond that he didn't move the switches? As per other input from people on here, when people are suicidal they often want to throw authorities off their trail. Or maybe he wanted to confuse the F/O so he didn't flick them back to run himself, or to just buy himself more time while the F/O tried to wrap his head around things? Maybe he didn't want the F/O to die knowing it was a suicide mission. Maybe we'll find out more in the final report or police investigation if things proceed that way. Maybe we'll never know. I acknowledge that this is my opinion and of course there could be things we don't yet know about, but I must say I'm surprised that some of the theories on this professional pilot forum are no more coherent or logical than those being sprouted on social media. |
Sailvi767
July 17, 2025, 12:02:00 GMT permalink Post: 11924345 |
I have not posted on here in many years, but I feel compelled to do so now. I am a current 787 pilot and I have previously flown most Boeing types and an Airbus too. I also have an extensive background and qualifications in human factors, training and assessment. Before anybody reads any further, perhaps acquaint yourself with the notion of Occam's razor. That is, the simplest explanation is the most likely explanation. I was certain that after the preliminary report was released the preposterous conspiracy theories would finally cease, but no! It's 2025 and humans can no longer help themselves. In my opinion the captain committed suicide here. Simple.
To those suggesting an electrical phantom turned the fuel control switches off without them moving: no. Ask yourselves this: what made one pilot (PF and F/O in my opinion) ask the other "why did you cut off?" Firstly, some context. The 787 fuel control switches make a VERY distinct metallic *CLICK* sound as they are operated. EVERY 787 pilot knows it and won't forget it. It is audible even at high thrust settings owing to the 787's exceptionally quiet engines and cockpit. After rotation the pilot flying is fixated on the HUD; rotating towards the TOGA reference line (~12 degrees pitch attitude) and putting the flight path vector over the flight guidance cue. One hand would be on the control column and the other on the thrust levers. Alternatively he could have had both hands on the control column. In either scenario, the pilot flying's (again, my opinion the F/O's) inboard arm would block his peripheral view (he's focused on the HUD, remember) of the center pedestal and the fuel control switches. HE WOULD NOT SEE THE PM TURN THE FUEL CONTROL SWITCHES OFF. Ipso facto. We know the F/O was PF from the report. If the F/O stopped flying the aircraft and reached down to move the FCS from cutoff to run the captain would've plainly seen the whole thing. I can't imagine "why did you cutoff?" would be his words of choice! More like "WTF ARE YOU DOING?!?" More to the point, if the PF (F/O) did stop flying and reach down to cut one engine off, the captain would have had time to either stop him flicking the second FCS off or at least quickly flick them both back to run and potentially save the day. This plainly did not happen. So it was almost certainly the PM (Capt) that moved the fuel control switches. So what would make the PF ask the PM "why did you cut off?" if he couldn't see it happen? You would never assume with a loss of thrust that the switches had been turned off. Never. It's not a procedure. It's not a thing. Bird strike? Sure. Fuel Contam? Maybe. But the point is, in the heat of battle at 150 odd feet, you'd never jump to the conclusion that the fuel control switches were off. Never. So what triggered the PF asking the PM why he cutoff? Because he HEARD the fuel control switches move from run to cutoff, that is why. He heard those distinctive *CLICK* sounds (and yes, you can easily flick them both in less than a second FWIW) followed by the engines immediately rolling back. He would then have looked down at the switches and noticed they were in cutoff. The point to be made here is that the switches were moved by the captain. They made their distinct sound. There were no phantoms. They cannot move on their own. They didn't simultaneously fail. This drew the PF's attention away from flying and triggered the question "why did you cutoff"? Inadvertent selection of the wrong switches? No. The PM was a training captain with thousands of hours experience on the jet. I asked one of our most experienced examiners how many times he'd seen that done. The answer was "zero". Even the stab switches next to them. They're red, guarded and are of a completely different shape and operation. Gear or flap? Come on. I think we're starting to stretch things a bit now. EVEN IF it was inadvertent switching. The INSTANT you'd made that error, you'd go "oh whoops", and flick them back to run. I know startle... I teach it. This is different. You don't flick the fuel control switches off, hear the engines roll back and sit there wondering what happened for 10 seconds AFTER THE F/O JUST ASKED YOU IF YOU CUTOFF! You did something that had an instant effect on the flight. The report indicates that "why did you cutoff" was asked just after both engines rolled back. But it took another 10 seconds to flick the FCS' back to run. If it was inadvertent, the instant the other pilot called out your error you'd correct it. The report makes it clear that there was 10 seconds between that happening. 10 seconds is a LIFETIME in that situation. The training captain knew what he was doing. He only switched the FCS' back to run once he knew it was moot. So, why did he respond that he didn't move the switches? As per other input from people on here, when people are suicidal they often want to throw authorities off their trail. Or maybe he wanted to confuse the F/O so he didn't flick them back to run himself, or to just buy himself more time while the F/O tried to wrap his head around things? Maybe he didn't want the F/O to die knowing it was a suicide mission. Maybe we'll find out more in the final report or police investigation if things proceed that way. Maybe we'll never know. I acknowledge that this is my opinion and of course there could be things we don't yet know about, but I must say I'm surprised that some of the theories on this professional pilot forum are no more coherent or logical than those being sprouted on social media. As to not putting out the CVR there is always tremendous outside pressure on an investigation of this scale. Air India is important to the nation. As someone else mentioned when the final report is published it will be old news. Time works for Air India in this case. They appear to finally be making solid progress on a return to financial solvency. The powers to be are not going to jeopardize that turnaround. The answers will come with the final report at a time when it will do far less damage to Air India. |