June 18, 2025, 01:18:00 GMT
permalink Post: 11904818
I wouldn't be surprised.
The speed should be at least at V2 and probably higher. Why would the ATS not just hold that speed, albeit being a shock to the crew. Within a few seconds I'll bet the throttles would end up back in the forward position as the ATS says "hey, we're slowing down fast here!". It would be ugly but I can't see that the jet's going to drop out of the sky. The throttles aren't going to come right back and stay right back.
The speed should be at least at V2 and probably higher. Why would the ATS not just hold that speed, albeit being a shock to the crew. Within a few seconds I'll bet the throttles would end up back in the forward position as the ATS says "hey, we're slowing down fast here!". It would be ugly but I can't see that the jet's going to drop out of the sky. The throttles aren't going to come right back and stay right back.
From one of the previous scenarios if capture at a way low altitude occurred they`d (IIRC correctly) engage in SPD mode resulting in a significant loss of thrust as they attempted to maintain speed assuming a level off. Presumably after this when the PF continued a climb (regardless of flight director) they`d come forward after this loss of thrust to attempt to meet commanded speed—V2 or V2+15 or whatever—but there`d be a lag. But I`ve never misset the MCP to a way low altitude in flight or the sim (not a holier than thou thing) so I`m not entirely sure how how the autothrottles would behave.
More than one crew has failed to push them to the stops when things went south.
And the reverse is true; when the second MCAS accident happened IIRC the autothrottles stayed in THR REF due to task saturation by the crew. Exacerbating the condition and ultimately resulting in an accident.
June 18, 2025, 15:54:00 GMT
permalink Post: 11905352
I'd like to stick my neck out and say what I think I know. And I do mean "know", not what I think "likely" or "possible".
1. The aircraft reached an altitude AGL rather more than one wingspan. This can be clearly seen in the still from the CCTV video posted by Cape Bloggs on 2025-06-18 at 0401. The 787-8 wingspan is 197+ ft. So it got at least 200 feet up in the air. (Info from CCTV screen shot.)
2. (a) Ground effect on lift essentially disappears on TO when the wheels are at screen height. (Info from an eminent colleague who performed the analysis.) I believe it follows that (b) he didn't get up to 200 ft by performing a zoom climb on unstick. It further follows that (c) there must have been some initially adequate lift out of GE to establish for a few seconds positive RoC.
3. The FR24 graphic posted by Musician shows that the aircraft became initially airborne "as usual", compared with other TO profiles. (Info from FR24.)
4. The aircraft lacked adequate thrust even to maintain altitude shortly after unstick.
5. Flaps 5 is minimal for TO. If you don't set it, you are told very clearly that you are misconfigured, well before TO roll. (Info from others.)
6. At Flaps 5 and likely loading (fuel, PAX, token sum for baggage) and in the atmospheric conditions pertaining, there is more than enough nominal thrust available to establish positive RoC. That obviously also holds for Flaps-more-than-5. (Info from others.)
I am not au fait with audio spectral analysis so, unlike some others here, including some whose views and experience I value highly, I am agnostic at this point about the RAT. (This is neither to deprecate those who performed this analysis, nor the views of those who know more about practical spectral analysis than I do and are convinced by it.)
Now for my personal inference so far from this. Items 2 and 3 above suggest to me that the aircraft was adequately configured to conduct a normal TO and initially establish positive RoC for a second or two. For me, the big question is: why wasn't there adequate thrust to maintain that? (We've been talking about those possibilities for some days now - I won't attempt to summarise.)
PBL
1. The aircraft reached an altitude AGL rather more than one wingspan. This can be clearly seen in the still from the CCTV video posted by Cape Bloggs on 2025-06-18 at 0401. The 787-8 wingspan is 197+ ft. So it got at least 200 feet up in the air. (Info from CCTV screen shot.)
2. (a) Ground effect on lift essentially disappears on TO when the wheels are at screen height. (Info from an eminent colleague who performed the analysis.) I believe it follows that (b) he didn't get up to 200 ft by performing a zoom climb on unstick. It further follows that (c) there must have been some initially adequate lift out of GE to establish for a few seconds positive RoC.
3. The FR24 graphic posted by Musician shows that the aircraft became initially airborne "as usual", compared with other TO profiles. (Info from FR24.)
4. The aircraft lacked adequate thrust even to maintain altitude shortly after unstick.
5. Flaps 5 is minimal for TO. If you don't set it, you are told very clearly that you are misconfigured, well before TO roll. (Info from others.)
6. At Flaps 5 and likely loading (fuel, PAX, token sum for baggage) and in the atmospheric conditions pertaining, there is more than enough nominal thrust available to establish positive RoC. That obviously also holds for Flaps-more-than-5. (Info from others.)
I am not au fait with audio spectral analysis so, unlike some others here, including some whose views and experience I value highly, I am agnostic at this point about the RAT. (This is neither to deprecate those who performed this analysis, nor the views of those who know more about practical spectral analysis than I do and are convinced by it.)
Now for my personal inference so far from this. Items 2 and 3 above suggest to me that the aircraft was adequately configured to conduct a normal TO and initially establish positive RoC for a second or two. For me, the big question is: why wasn't there adequate thrust to maintain that? (We've been talking about those possibilities for some days now - I won't attempt to summarise.)
PBL
But you ask..... How can an aircraft possibly get airborne with a stalled wing? Look at Air France 7775 . At rotate the wing was already stalled (albeit for different reasons) but the airborne profile of the aircraft was rather similar to Air India.
June 18, 2025, 17:38:00 GMT
permalink Post: 11905418
Usually on takeoff LNAV and VNAV are armed. During the takeoff roll the autothrottle system goes in to HOLD mode at 80kts.
At that point the FMAs read:
At 50' LNAV engages and the FMAs change to:
At 400' VNAV engages and the FMAs change to:
The height is referenced to a barometric snapshot taken during the take off roll at 100kts.
If an altitude is captured before VNAV engagement (totally bizarre to capture an altitude of less than 400') then the FMAs would change to:
SPD | LNAV | ALT
At that point the FMAs read:
At 50' LNAV engages and the FMAs change to:
At 400' VNAV engages and the FMAs change to:
The height is referenced to a barometric snapshot taken during the take off roll at 100kts.
If an altitude is captured before VNAV engagement (totally bizarre to capture an altitude of less than 400') then the FMAs would change to:
SPD | LNAV | ALT
Could explain the witnesses thought that power came back up before they hit but witness recollections post traumatic event as well as second hand reporting need some time to settle in before accurate facts come out.
Last edited by Shep69; 18th June 2025 at 17:53 .
June 18, 2025, 17:52:00 GMT
permalink Post: 11905425
Last edited by BraceBrace; 18th June 2025 at 18:04 .
June 19, 2025, 09:42:00 GMT
permalink Post: 11905873
Contrary to something I read in the other closed thread, the 787 FMS doesn't perform takeoff calculations; in fact the code which does that was removed prior to initial certification.
The 787 relies on takeoff data computed by dispatch or in the EFB (Electronic Flight Bag), both provided via datalink to the FMS.
The latter can be subject to all manner of erroneous crew inputs if they're careless and aren't doing a good job of cross checking.
Garbage in, garbage out as the saying goes.
The 787 relies on takeoff data computed by dispatch or in the EFB (Electronic Flight Bag), both provided via datalink to the FMS.
The latter can be subject to all manner of erroneous crew inputs if they're careless and aren't doing a good job of cross checking.
Garbage in, garbage out as the saying goes.
I have been using EFB all my life and can only confirm that every company has very strict procedures. And history has shown that if they are not followed, the end result is usually a tailstrike, not a stall inflight. As thrust can be increased on the spot, flaps influence (as long as not up) is highly overrated (as is in this thread) as there isn't that big of a difference between the V2 values of different flap settings.
The Air India crash is a obvious case of loss of thrust on both engines. The flight trajectory resembles a typical "too high and held off flare" that happens many times on training flights which with low time ab-initio's, that without correct re-input of thrust, leads to tailstrike. The nose up attitude, tail impact first shows engines were idle or out up to impact. Both engines to be clear, otherwise the aircraft would start to roll due to reduced rudder efficiency at low speed and higher thrust on one side. That's just pure physics, and physics can't be changed.
June 19, 2025, 11:08:00 GMT
permalink Post: 11905928
I have to agree with you
PBL
. It is amazing that people are still arguing about the height the aircraft reached during the first 11s of the flight. It is almost measurable to the metre from the aircraft wingspan on the video. Do not mistake the power required to reach Vr within in the TORA with the power required to maintain a stable climb at V2 to V2+10 in the second and third segments. They are very different numbers, that's why Perf A is one of the dark arts of aviation! It is quite probable that this aircraft rotated below a suitable Vr speed for the weight and ambient conditions and was unable to establish a stable climb due lack of applied power. Big engines take time to spool up, your immediate future depends on how late you recognise the situation and go for TOGA.
But you ask..... How can an aircraft possibly get airborne with a stalled wing? Look at Air France 7775 . At rotate the wing was already stalled (albeit for different reasons) but the airborne profile of the aircraft was rather similar to Air India.
But you ask..... How can an aircraft possibly get airborne with a stalled wing? Look at Air France 7775 . At rotate the wing was already stalled (albeit for different reasons) but the airborne profile of the aircraft was rather similar to Air India.
June 19, 2025, 19:04:00 GMT
permalink Post: 11906277
Interesting thread towards the end, regarding the previous TCMA malfunction
on landing
: (pprune archived thread 617426, can\x92t post links yet)
according to Dave Therhino who claimed to have seen a detailed report, the TCMA would initialise the thrust contour logic when touching the ground. This was nominally not an issue, as the throttles and engine would be close to idle. However, if the reverser was briefly deployed right before weight on wheels, and then cancelled when the wheels touched, TCMA would see high thrust but throttles at idle and trigger.
But this was supposedly fixed and all FADECs updated. Plus, during take-off there should not be such large fluctuation in throttle position or thrust, so intermittent switching of ground-air-ground should not cause an issue.
Also, according to tdracer V2 overspeed protection cuts thrust so quickly, that if it triggered (via TCMA or whatever other reason) it was likely after the plane had lifted off the ground. I wonder though if there\x92s still enough kinetic energy to fly the profile of the incident flight with the engines cut right around rotation.
Also, would hydraulics go out so quickly, that wheels would not retract? Wonder if a faulty WoW sensor could be a contributing factor and would also not manifest itself as the wheels not retracting :thinking
according to Dave Therhino who claimed to have seen a detailed report, the TCMA would initialise the thrust contour logic when touching the ground. This was nominally not an issue, as the throttles and engine would be close to idle. However, if the reverser was briefly deployed right before weight on wheels, and then cancelled when the wheels touched, TCMA would see high thrust but throttles at idle and trigger.
But this was supposedly fixed and all FADECs updated. Plus, during take-off there should not be such large fluctuation in throttle position or thrust, so intermittent switching of ground-air-ground should not cause an issue.
Also, according to tdracer V2 overspeed protection cuts thrust so quickly, that if it triggered (via TCMA or whatever other reason) it was likely after the plane had lifted off the ground. I wonder though if there\x92s still enough kinetic energy to fly the profile of the incident flight with the engines cut right around rotation.
Also, would hydraulics go out so quickly, that wheels would not retract? Wonder if a faulty WoW sensor could be a contributing factor and would also not manifest itself as the wheels not retracting :thinking
June 20, 2025, 12:01:00 GMT
permalink Post: 11906896
Originally Posted by
Musician
Assume an object travels at 200 knots and its speed decays to 120 knots (100m/s to 60m/s). The kinetic energy lost thereby suffices to elevate that object by ~1000 ft. (320m) in a vacuum, i.e. disregarding drag. In other words, if 75% of the kinetic energy was lost through air resistance (drag), the aircraft could still climb more than 200 feet.
Having done many a takeoff sitting with the nose pointed skyward after liftoff, you just know that if both engines stopped, you would almost immediately stop going up. When you lose only one you have to be quick getting the nose down to keep the speed. If you lost both, you're not going much higher.
Last edited by Senior Pilot; 20th June 2025 at 12:07 . Reason: Remove quote of a deleted post
June 20, 2025, 12:31:00 GMT
permalink Post: 11906925
In this case, not being a 787 jock, my WAG would be a V2 of 165, so they'd be at ~180, and Vref would be at least ~160 (422,000lb, at flap 5). Once those engines cut, it wasn't going much higher at all. Bit of a zoom of possibly 100ft max, IMO. So I doubt the engines stopped at liftoff.
Having done many a takeoff sitting with the nose pointed skyward after liftoff, you just know that if both engines stopped, you would almost immediately stop going up. When you lose only one you have to be quick getting the nose down to keep the speed. If you lost both, you're not going much higher.
Having done many a takeoff sitting with the nose pointed skyward after liftoff, you just know that if both engines stopped, you would almost immediately stop going up. When you lose only one you have to be quick getting the nose down to keep the speed. If you lost both, you're not going much higher.
June 20, 2025, 15:49:00 GMT
permalink Post: 11907075
Disclaimer: the numbers I mention are from publicly available sources, namely Wiki (for the ZFW weight calculation) and a Boeing FCOM dated 2010, and my own estimations.
IMO, if those engines failed just after rotation, there is no way that jet would have got anywhere near 200ft, especially if the fuel was "cut off", as opposed to back to Idle.
At 420k lbs (310k lb ZFW+110k lb Fuel), the (takeoff) V2 Flap 5 is 157kts. The (landing) Vref for Flap 5 I estimate to be at least 160kts (the FCOM I have has no figures for Flap 5 landings; F20 Vref is 154; the manoeuvre speed for Flap 5 is 189). Typically, you'd probably be at V2+15 when you get established in the climb after rotation.
No. With a pitch attitude of around 15\xb0, that's quite a bit of weight being supported not only by the wings but by the engine thrust vector. Cut that and you stop going up very quickly. Note Sailvi's comment above.
ANY reduction in pitch attitude would cause the climb to cease immediately. These aircraft are going so slowly, relatively, and the drag is so high that any small change in pitch attitude will cause an increase in descent rate with very little increase in speed (or no lessening of deceleration).
Not IMO. Basically, the only reason this jet is flying is because of the whopping long thrust vector out the back. It's already almost back at minimum speed anyway for flap 5 so there is very speed to trade. In this case, I wouldn't be trading anything, because the speed reduction rate would be too fast.
My estimate is around 200ft (one wingspan) and I hypothesise the engines were producing plenty of thrust until about 7 seconds, before it stops climbing at around 12 seconds after liftoff.
@Brace , I think you're exaggerating the residual thrust effect at lower RPMs. Of course 70% would get you round the pattern but you're at a much lower drag config and you're going much faster, again less drag. And are improved-climb takeoffs in the 787-8 even a thing? I can't see a two-stage rotation.
I've made up a YT combo video:
Strange, as I would have estimated this quite differently based on layman's intuition. If one assumes average values, then the approximate flight profile of AI171 according to layman's guidance certainly fits a situation in which the engines failed at or even very shortly before rotation.
Is VR about 20 to 30 knots above the landing speed?
Would these 20 to 30 knots of additional energy be sufficient to lift the aircraft to a good 200 ft during and after rotation?
If the angle of attack is then successively reduced, wouldn't the airplane still have enough lift to glide for a few seconds before losing all or nearly all lift?
Wouldn't it be the case that if the thrust had only ceased five seconds after rotation, the aircraft would then have reached a good 250 ft with the engines still running and then another good 200 ft in normal conditions before the speed was used up to about 150 kn?
AI171 probably didn't reach an altitude of 400 to 500 ft above ground (in relation to the airport), did it?
@Brace , I think you're exaggerating the residual thrust effect at lower RPMs. Of course 70% would get you round the pattern but you're at a much lower drag config and you're going much faster, again less drag. And are improved-climb takeoffs in the 787-8 even a thing? I can't see a two-stage rotation.
I've made up a YT combo video:
June 20, 2025, 18:31:00 GMT
permalink Post: 11907188
In this case, not being a 787 jock, my WAG would be a V2 of 165, so they'd be at ~180, and Vref would be at least ~160 (422,000lb, at flap 5). Once those engines cut, it wasn't going much higher at all. Bit of a zoom of possibly 100ft max, IMO. So I doubt the engines stopped at liftoff.
Having done many a takeoff sitting with the nose pointed skyward after liftoff, you just know that if both engines stopped, you would almost immediately stop going up. When you lose only one you have to be quick getting the nose down to keep the speed. If you lost both, you're not going much higher.
Having done many a takeoff sitting with the nose pointed skyward after liftoff, you just know that if both engines stopped, you would almost immediately stop going up. When you lose only one you have to be quick getting the nose down to keep the speed. If you lost both, you're not going much higher.
June 21, 2025, 04:06:00 GMT
permalink Post: 11907468
Just to summarize. There appears to be fairly wide consensus as to what happened:
On that basis, there is still some mileage in establishing the aircraft speed in the last moments before takeoff. There is definitely mileage in identifying a single point of failure that would cause the engines to shut down; other than fuel contamination/vapour issues. I suspect that the official investigation is not all that further ahead of this thread. Without useful data from the EAFR they have to rely on forensics and history. Enough has been leaked to know the engines were no more than windmilling at impact.
A high level of interest will continue given there are still remaining questions whether the reliability of Boeing machinery is implicated. That is not to mention the hundreds of people closely affected by this tragedy that are looking for reasons why it happened. Perhaps an interim report is now overdue?
- Up to V1 it appeared normal and the pilots did not abort.
- Loss of thrust very close to V2 rotate or shortly thereafter.
- Loss of electrical and hydraulics resulting in deployment of RAT seconds after being airborne.
- Mayday transmission seconds after takeoff (although it may have occurred around V2, the timing has not been established).
- Gear tilted forward suggesting gear retraction was initiated but not completed.
- All followed by glide to impact from AGL of little more than 100 feet.
On that basis, there is still some mileage in establishing the aircraft speed in the last moments before takeoff. There is definitely mileage in identifying a single point of failure that would cause the engines to shut down; other than fuel contamination/vapour issues. I suspect that the official investigation is not all that further ahead of this thread. Without useful data from the EAFR they have to rely on forensics and history. Enough has been leaked to know the engines were no more than windmilling at impact.
A high level of interest will continue given there are still remaining questions whether the reliability of Boeing machinery is implicated. That is not to mention the hundreds of people closely affected by this tragedy that are looking for reasons why it happened. Perhaps an interim report is now overdue?
Last edited by wheelsright; 21st June 2025 at 04:24 .
June 30, 2025, 13:32:00 GMT
permalink Post: 11913628
Thank you for that answer, edge cases do abound in complex systems, but would not moving the throttles forward by hand (as the thrust was beginning to reduce {for that strange reason}) overcome that and restore thrust?
(As I don't fly the 787, I may be missing something basic on how the systems work).
(As I don't fly the 787, I may be missing something basic on how the systems work).
THRUST Asymmetry PROTECTION.
"For an engine-out condition, Thrust Asymmetry Protection (TAP) reduces thrust on the operating engine to ensure there is sufficient rudder for directional control. TAP reduces thrust when the airspeed decreases below approximately V2 on a takeoff or below approximately VREF on a go-around. Once speed is increased above V2/VREF, TAP increases thrust."
From what we know so far, it does seem the engines were not producing sufficient thrust, during a period when it would also be crucial to maintain electrical output for the electro-hydraulic systems and critical electrical loads.
Reduced electrical output could explain the failure of the gear to complete retraction, maybe caused by a generator failing at the worst possible moment.
If there was an EFATO, the ability of the remaining generators to provide sufficient power might become questionable, as is highlighted with the load shedding system.
Other features which are unique to the 787 could be contributing factors in explaining the accident.
It is known the 787 will generally employ an extended take-off roll, and a relatively higher V1 and Vr, and also climb out less steeply than other aircraft. Using more of the runway would reduce the margin for aborted take offs.
With the evident lack of thrust early in the climb out, and failure to retract the gear, if V2 had not been maintained, the TAP system would have reduced thrust even further. Manually increasing thrust will be inhibited.
June 30, 2025, 18:57:00 GMT
permalink Post: 11913849
I found descriptions on the systems of the 787 were easily discovered online, and while I have no hands-on experience of aircraft related matters, I do have experience in wider electrical theory and maintenance.
THRUST Asymmetry PROTECTION.
"For an engine-out condition, Thrust Asymmetry Protection (TAP) reduces thrust on the operating engine to ensure there is sufficient rudder for directional control. TAP reduces thrust when the airspeed decreases below approximately V2 on a takeoff or below approximately VREF on a go-around. Once speed is increased above V2/VREF, TAP increases thrust."
From what we know so far, it does seem the engines were not producing sufficient thrust, during a period when it would also be crucial to maintain electrical output for the electro-hydraulic systems and critical electrical loads.
Reduced electrical output could explain the failure of the gear to complete retraction, maybe caused by a generator failing at the worst possible moment.
If there was an EFATO, the ability of the remaining generators to provide sufficient power might become questionable, as is highlighted with the load shedding system.
Other features which are unique to the 787 could be contributing factors in explaining the accident.
It is known the 787 will generally employ an extended take-off roll, and a relatively higher V1 and Vr, and also climb out less steeply than other aircraft. Using more of the runway would reduce the margin for aborted take offs.
With the evident lack of thrust early in the climb out, and failure to retract the gear, if V2 had not been maintained, the TAP system would have reduced thrust even further. Manually increasing thrust will be inhibited.
THRUST Asymmetry PROTECTION.
"For an engine-out condition, Thrust Asymmetry Protection (TAP) reduces thrust on the operating engine to ensure there is sufficient rudder for directional control. TAP reduces thrust when the airspeed decreases below approximately V2 on a takeoff or below approximately VREF on a go-around. Once speed is increased above V2/VREF, TAP increases thrust."
From what we know so far, it does seem the engines were not producing sufficient thrust, during a period when it would also be crucial to maintain electrical output for the electro-hydraulic systems and critical electrical loads.
Reduced electrical output could explain the failure of the gear to complete retraction, maybe caused by a generator failing at the worst possible moment.
If there was an EFATO, the ability of the remaining generators to provide sufficient power might become questionable, as is highlighted with the load shedding system.
Other features which are unique to the 787 could be contributing factors in explaining the accident.
It is known the 787 will generally employ an extended take-off roll, and a relatively higher V1 and Vr, and also climb out less steeply than other aircraft. Using more of the runway would reduce the margin for aborted take offs.
With the evident lack of thrust early in the climb out, and failure to retract the gear, if V2 had not been maintained, the TAP system would have reduced thrust even further. Manually increasing thrust will be inhibited.
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
July 12, 2025, 00:14:00 GMT
permalink Post: 11920031
July 15, 2025, 05:22:00 GMT
permalink Post: 11922663
Air India 171: Energy-Consistent Flight Profile
This energy-based model illustrates Air India 171's flight profile from liftoff to impact. It uses the initial data point from FlightRadar24 of 184 kts G/S, 21 ft height, Google Earth for the crash location, and CCTV footage (originally posted on X) for timing.
A key observation is the calculated average ground speed of 150 knots from the initial point, just after takeoff, to the crash site, derived using the CCTV elapsed time. The model incorporates "best-guess" mid-points inferred from the CCTV footage, which help depict approximate indicated airspeeds consistent with the aircraft's energy state throughout the flight.
The analysis assumes zero thrust during the flight and an average Lift-to-Drag ratio of approximately 12. For this model, a takeoff mass of 210 tonnes and an estimated V2 of 160 knots were used.
Note: This analysis was conducted prior to the release of the AAIB preliminary report, and therefore does not account for the correct take off mass and the actual V2 of 162. The differences are small and as this is a rough best guess, it\x92s just a basic energy model to show the possible trade between speed and height. No account was made of an engine spooling up at the end of the flight. Visual review of the video suggests the thrust from any restarting engine must have been very low, as no significant yaw is discernible.
July 15, 2025, 10:55:00 GMT
permalink Post: 11922831
With what we know now from the preliminary report that option seems to be a good candidate as the source of initiation for an action slip. Both the PF instead of calling Gear Up Action Slipping and operating the Cutoff Switches, or the PM instead of calling Positive Rate doing so would fit that scenario and timeline.