July 13, 2025, 18:03:00 GMT
permalink Post: 11921493
Electrical effects of engine rollback
As I understand it from previous discussions, without the APU, all electrical power except for that DC power provided by battery to essential systems would have been lost.
With the copilot as PF, would he have lost his instrument displays? If so, possibly additional startle effect and workload for him.
Why did the ADS-B information keep going on for so long? My understanding from previous threads was that loss of ADS-B was considered an indication of loss of electrical power.
What else would be expected with loss of power?
Some general speculation: I find it hard to understand the long delay from what must have been the onset of obvious issues to the time the first engine is set to "RUN". I wonder if much more cockpit dialog intervened, e.g. PF requesting PM to turn the fuel switches back on (since he had his hands full), and eventually operating the switches himself, with the delay and time gap between the two switches being turned to "RUN" being attributable to being preoccupied with flying the aircraft under trying conditions.
July 13, 2025, 18:39:00 GMT
permalink Post: 11921522
I would like to raise a subject that I don't believe has been discussed here since the Preliminary Report was published, namely what happened to the aircraft's electrical systems as a consequence of the dual engine rollback and thereafter (RAT deployment, partial engine recovery, etc.). Apologies if I've missed posts on this topic here, but I have tried to review all of this thread quickly after previously reading most of it in detail.
As I understand it from previous discussions, without the APU, all electrical power except for that DC power provided by battery to essential systems would have been lost.
With the copilot as PF, would he have lost his instrument displays? If so, possibly additional startle effect and workload for him.
Why did the ADS-B information keep going on for so long? My understanding from previous threads was that loss of ADS-B was considered an indication of loss of electrical power.
What else would be expected with loss of power?
Some general speculation: I find it hard to understand the long delay from what must have been the onset of obvious issues to the time the first engine is set to "RUN". I wonder if much more cockpit dialog intervened, e.g. PF requesting PM to turn the fuel switches back on (since he had his hands full), and eventually operating the switches himself, with the delay and time gap between the two switches being turned to "RUN" being attributable to being preoccupied with flying the aircraft under trying conditions.
As I understand it from previous discussions, without the APU, all electrical power except for that DC power provided by battery to essential systems would have been lost.
With the copilot as PF, would he have lost his instrument displays? If so, possibly additional startle effect and workload for him.
Why did the ADS-B information keep going on for so long? My understanding from previous threads was that loss of ADS-B was considered an indication of loss of electrical power.
What else would be expected with loss of power?
Some general speculation: I find it hard to understand the long delay from what must have been the onset of obvious issues to the time the first engine is set to "RUN". I wonder if much more cockpit dialog intervened, e.g. PF requesting PM to turn the fuel switches back on (since he had his hands full), and eventually operating the switches himself, with the delay and time gap between the two switches being turned to "RUN" being attributable to being preoccupied with flying the aircraft under trying conditions.
There seems to be a period around second 12/13 post V1 where engines are (or should) be likely below idle, but prior to RAT power generation.
Note that the report explicitly states the RAT started providing hydraulic power 5 seconds after engine shutdown commenced. It doesn't reference electrical power. So we don't know whether this was at the same time - others may clarify re: RAT operation.
But either way, it would appear there would be a gap in power (which, incidentally, would tie in with the survivor commentary). But yet ADS data continued.
If in fact there was a momentary loss of power then that would contribute heavily to the startle and "delay" in refiring (although comments here make me think there wasn't really such a delay anyway).
(And incidentally would make what appears to be a really rather valiant attempt to save the aircraft even more impressive)
July 13, 2025, 18:44:00 GMT
permalink Post: 11921524
The ADS-B data collected by FR24 leave the aircraft at 172 knots
Please tell me how recoverable that is, with hypothetical 95% thrust on both engines
edit: reviewed fr24 data and adjusted time covered; I think it did decelerate to approximately 155 knots in 10 seconds, based on -3knots/second.
July 13, 2025, 18:55:00 GMT
permalink Post: 11921532
July 13, 2025, 19:29:00 GMT
permalink Post: 11921564
Yes.
The ADS-B data collected by FR24 leave the aircraft at 172 knots
8 seconds
4 seconds into the outage. Vr was 155 knots per the report. The preliminary report also says it crashed at 8⁰ nose-up attitude, which was after the "flare".
Please tell me how recoverable that is, with hypothetical 95% thrust on both engines
2
6 seconds later.
edit: reviewed fr24 data and adjusted time covered; I think it did decelerate to approximately 155 knots in 10 seconds, based on -3knots/second.
The ADS-B data collected by FR24 leave the aircraft at 172 knots
Please tell me how recoverable that is, with hypothetical 95% thrust on both engines
edit: reviewed fr24 data and adjusted time covered; I think it did decelerate to approximately 155 knots in 10 seconds, based on -3knots/second.
Beware of comparing the speeds from ADS-B, which are groundspeeds, with those from the report, which are IAS.
July 13, 2025, 20:27:00 GMT
permalink Post: 11921617
Quote: Originally Posted by
Contact Approach
But there is evidence, pretty clear evidence!
The "evidence" might be available, but I disagree it is available to us. I assert the prelim report has been deliberately sanitised to prevent us (i.e. everybody outside the AAIB circle) being given enough 'evidence' to make certain conclusions.
You/others might not like it, some might say it is obvious (I say not), but I think it is carefully worded enough to imply what might have happened, but nothing is clear - intentionally.
But there is evidence, pretty clear evidence!
You/others might not like it, some might say it is obvious (I say not), but I think it is carefully worded enough to imply what might have happened, but nothing is clear - intentionally.
July 13, 2025, 20:37:00 GMT
permalink Post: 11921627
Quote: Originally Posted by
Contact Approach
But there is evidence, pretty clear evidence!
The "evidence" might be available, but I disagree it is available to us. I assert the prelim report has been deliberately sanitised to prevent us (i.e. everybody outside the AAIB circle) being given enough 'evidence' to make certain conclusions.
You/others might not like it, some might say it is obvious (I say not), but I think it is carefully worded enough to imply what might have happened, but nothing is clear - intentionally.
But there is evidence, pretty clear evidence!
The "evidence" might be available, but I disagree it is available to us. I assert the prelim report has been deliberately sanitised to prevent us (i.e. everybody outside the AAIB circle) being given enough 'evidence' to make certain conclusions.
You/others might not like it, some might say it is obvious (I say not), but I think it is carefully worded enough to imply what might have happened, but nothing is clear - intentionally.
Suggesting otherwise is a bit insulting to the professionals who wade into debris fields, examine minute evidence, and have to try and work out how and why a catastrophe happened. It isn't a fun job, and it isn't done in isolation from a lot of expertise.
What the report does not contain are facts yet to be determined, and details unknown or uncertain at the time the rules required putting pen to paper. And if it is lacking in the sort of precision we would hope for, it is still the only factual report we have.
July 13, 2025, 20:39:00 GMT
permalink Post: 11921628
The event shows that it's really imperative to relight the engines as quickly as possible.
The preliminary report says it took about 5 seconds for the engines to spool down to idle. 14 CFR \xa7 33.73 - Power or thrust response requires a jet engine to reach 95% thrust from stabilized flight idle in not over 5 seconds. So with a sufficiently quick reaction, flipping the switches back after 5 seconds, they could've been back in business by the time they actually flipped the switches back.
So it's not "flip the switches 3 seconds after liftoff and you're unrecoverable"; to be unrecoverable, there must also be sufficient time for the engines to spool down enough.
Don't ask, "why did you cut the engines", flip them back on. Go for the E in PACE.
The preliminary report says it took about 5 seconds for the engines to spool down to idle. 14 CFR \xa7 33.73 - Power or thrust response requires a jet engine to reach 95% thrust from stabilized flight idle in not over 5 seconds. So with a sufficiently quick reaction, flipping the switches back after 5 seconds, they could've been back in business by the time they actually flipped the switches back.
So it's not "flip the switches 3 seconds after liftoff and you're unrecoverable"; to be unrecoverable, there must also be sufficient time for the engines to spool down enough.
Don't ask, "why did you cut the engines", flip them back on. Go for the E in PACE.
Secondly, once the plane started to sink, just getting useable thrust won’t save the day, there has to be enough lift to arrest the sink rate. That requires some altitude, a lot more than 200’.
July 13, 2025, 21:06:00 GMT
permalink Post: 11921654
Thank you for your reply! I'm aware you know more about ADS-B than I do, and I'm happy to learn.
As you know, I'm referring to the map view and data on https://www.flightradar24.com/blog/f...rom-ahmedabad/ .
That's what I thought at first, based on the time stamps.
08:08:50.87 last full ADS-B message (172 kts)
08:08:54 APU inlet door starts to open, per the report.
My problem here is that the report also says that the maximum speed was 180 knots IAS at about 08:08:42. And we have
2025-06-12T08:08:46.550875Z,8005ec,23.069138,72.625871,575
associated with 184 kts as the first ADS-B message in the sequence.
Given that the clocks of ADS-B receivers are sometimes off, I think this might actually represent the moment of maximum speed; but then the AFS-B clock would be 4 seconds fast.
And that's why I adjusted my times.
A way to cross-check would be to track the aircraft position over time from the point of rotation, or to use the new photo in the report that shows the RAT over the runway to triangulate where that was.
Yes.
Would low pressure and high temperature make IAS lower than ground speed, even with the 7 knot headwind?
Either way, if they were decelerating at approximately 3 knots per second, then they would've ended up at about 150 knots IAS, which is less than Vr.
When I look at the CCTV video, 13 seconds into the flight, the aircraft is just "over the hump" and starts descending, so that tracks.
At this point, I don't know what having the engines spool up instead of being dead weight would've done to that flight path; and how successfully the aircraft could've been recovered from that.
Maybe they had only 4 seconds to flip those switches, instead of 5 seconds?
Still, the best bet is to not ask questions, but flip these switches back ASAP, no?
As you know, I'm referring to the map view and data on https://www.flightradar24.com/blog/f...rom-ahmedabad/ .
08:08:50.87 last full ADS-B message (172 kts)
08:08:54 APU inlet door starts to open, per the report.
My problem here is that the report also says that the maximum speed was 180 knots IAS at about 08:08:42. And we have
2025-06-12T08:08:46.550875Z,8005ec,23.069138,72.625871,575
associated with 184 kts as the first ADS-B message in the sequence.
Given that the clocks of ADS-B receivers are sometimes off, I think this might actually represent the moment of maximum speed; but then the AFS-B clock would be 4 seconds fast.
And that's why I adjusted my times.
A way to cross-check would be to track the aircraft position over time from the point of rotation, or to use the new photo in the report that shows the RAT over the runway to triangulate where that was.
Beware of comparing the speeds from ADS-B, which are groundspeeds, with those from the report, which are IAS.
Would low pressure and high temperature make IAS lower than ground speed, even with the 7 knot headwind?
Either way, if they were decelerating at approximately 3 knots per second, then they would've ended up at about 150 knots IAS, which is less than Vr.
When I look at the CCTV video, 13 seconds into the flight, the aircraft is just "over the hump" and starts descending, so that tracks.
At this point, I don't know what having the engines spool up instead of being dead weight would've done to that flight path; and how successfully the aircraft could've been recovered from that.
Maybe they had only 4 seconds to flip those switches, instead of 5 seconds?
Still, the best bet is to not ask questions, but flip these switches back ASAP, no?
Last edited by Musician; 13th July 2025 at 21:36 .
July 13, 2025, 21:18:00 GMT
permalink Post: 11921673
July 13, 2025, 21:49:00 GMT
permalink Post: 11921703
A few observations
While IMO the Air India 171 preliminary report (
PR
) in some aspects leaves ample room for speculation rather than soothing it, let’s not loose sight of a straight forward assumption that what is presently known to AAIB India beyond what is explicitly stated in the
PR
, at least to AAIB India’s judgement (and I presume amongst others NTSB's as well), shouldn’t lead to any significantly different preliminary observations and conclusions than those made in the
PR
at this stage.
In other words, there shouldn't be at present other major known/established facts based on the EAFR readouts (2000+ parameters!), but for now not published, that could immediately lead to other observations/qualifications than those made in the present PR .
If there would be, this would actually mean the end of authority of air safety incident investigation and reporting around the globe as we have known it for the past decades.
In other words, there shouldn't be at present other major known/established facts based on the EAFR readouts (2000+ parameters!), but for now not published, that could immediately lead to other observations/qualifications than those made in the present PR .
If there would be, this would actually mean the end of authority of air safety incident investigation and reporting around the globe as we have known it for the past decades.
Last edited by D Bru; 13th July 2025 at 23:16 . Reason: finetuning of argument :)
July 13, 2025, 22:02:00 GMT
permalink Post: 11921714
Here is something I have not seen on this thread. In the UK, as I understand it, an accident investigation is lead by the AAIB, however if evidence is discovered that suggests a criminal act has taken place then the police lead the investigation with the AAIB in a supporting role. Here is the
memorandum of understanding [pdf]
describing this, sections 3.5 and 3.6 describe the difference.
I assume something of the same happens in India. However, I can not find any evidence online that a criminal investigation has been launched there and it seems AAIB (India) continues to lead the investigation.
This suggests that, with all the evidence gathered by the investigators so far (which is substantial), there are no grounds to conclude that a criminal act had been committed.
In other words, this is an accident and not deliberate.
I assume something of the same happens in India. However, I can not find any evidence online that a criminal investigation has been launched there and it seems AAIB (India) continues to lead the investigation.
This suggests that, with all the evidence gathered by the investigators so far (which is substantial), there are no grounds to conclude that a criminal act had been committed.
In other words, this is an accident and not deliberate.
If there's one factor which strikes me as pertinent to the AI171 prelim report, it's that it may have been written in the form we see, to help hold the question of criminality sufficiently distant that the investigators don't loose control of the investigation.
July 13, 2025, 22:20:00 GMT
permalink Post: 11921735
The short answer is that we wouldn't have CVR recordings if that was possible.
Basically, the cockpit voice recorder records the pilots incriminating themselves. It was only possible to get pilots to agree to have a CVR in the cockpit by assuring them it would only be used in accident investigations. For example, on the 787's EAFR you can read out the data on a laptop connected to the onboard network, but you can't read out the CVR unless you physically access the device.
Air accident investigations must safeguard that status. Their success depends on the guarantee that the investigation results can't be used to incriminate the pilots legally. But while courts cannot subpoena the CVR recording from the accident investigation, they wouldn't have to if the board released a full recording or even just a full transcript.
In my opinion, that is why this preliminary report is vague on who said what, and what exactly was said.
The CVR must not become a constant "anything you say can and will be used against you in a court of law" in the cockpit.
I'd be happy if any lawyers in the thread (e.g. WillowRun 6-3 ) could correct or confirm.
Basically, the cockpit voice recorder records the pilots incriminating themselves. It was only possible to get pilots to agree to have a CVR in the cockpit by assuring them it would only be used in accident investigations. For example, on the 787's EAFR you can read out the data on a laptop connected to the onboard network, but you can't read out the CVR unless you physically access the device.
Air accident investigations must safeguard that status. Their success depends on the guarantee that the investigation results can't be used to incriminate the pilots legally. But while courts cannot subpoena the CVR recording from the accident investigation, they wouldn't have to if the board released a full recording or even just a full transcript.
In my opinion, that is why this preliminary report is vague on who said what, and what exactly was said.
The CVR must not become a constant "anything you say can and will be used against you in a court of law" in the cockpit.
I'd be happy if any lawyers in the thread (e.g. WillowRun 6-3 ) could correct or confirm.
July 13, 2025, 22:36:00 GMT
permalink Post: 11921747
While this is thread is still deeply into hamster wheel status, there are some valuable inputs being made. I'll try to continue with that...
Thrust lever position post-accident - it takes very little force to move the thrust levers, a little more than one pound-force at the knob. I'd be very surprised if the post impact position was the same as pre-impact (and lever angle is recorded on the FDR, so the investigators know where they were). In short - the post-accident lever position is not meaningful.
Fuel condition switch position detents - if the Indian investigators had any reason to believe that a failed or inoperative detent was a contributing fact, the authorities would have ordered a fleet-wide inspection (especially since it literally takes only seconds to do the inspection - the paperwork would take many times longer than the actual inspection).
Engine restart (i.e. "Quick Windmill Relight"): Even if the igniters were firing, at high power they won't actually spark (the electrical resistance or the air at several hundred psi prevents a spark) - so they won't spark until you get down somewhere near idle if you're close to sea level. Once the engine has dropped below the min idle, it takes a long time for it accelerate back to even an idle condition. At takeoff power, the compressor components get very hot - do a power cut the air coming in the compressor gets heated by the residual heat in the compressor. This in turn limits how fast you can add fuel in the burner without excessively back pressuring the compressor and causing a compressor stall. So it actually takes longer for the engine to accel to idle that it would during a normal (cold engine) start. The 5 seconds to 95% accel requirement referenced earlier is from a stable 'high' idle (we typically call it 'approach idle' since it's automatically selected when landing flaps are selected). Approach idle is ~10% N2 higher than the in-flight minimum idle, so that takes several more seconds. Bottom line, after initiating the Quick Windmill Relight, you're not going to have usable thrust for at least 30 seconds - probably closer to 60 seconds.
For all the complaining about this preliminary report, it actually goes into more detail than is typical.
BTW, my money is still on the 'muscle memory/action slip' or whatever you want to call it. I can easily imagine a scenario along the line of 'why did you turn off the fuel' - 'I didn't - oh wait - oh
...
Thrust lever position post-accident - it takes very little force to move the thrust levers, a little more than one pound-force at the knob. I'd be very surprised if the post impact position was the same as pre-impact (and lever angle is recorded on the FDR, so the investigators know where they were). In short - the post-accident lever position is not meaningful.
Fuel condition switch position detents - if the Indian investigators had any reason to believe that a failed or inoperative detent was a contributing fact, the authorities would have ordered a fleet-wide inspection (especially since it literally takes only seconds to do the inspection - the paperwork would take many times longer than the actual inspection).
Engine restart (i.e. "Quick Windmill Relight"): Even if the igniters were firing, at high power they won't actually spark (the electrical resistance or the air at several hundred psi prevents a spark) - so they won't spark until you get down somewhere near idle if you're close to sea level. Once the engine has dropped below the min idle, it takes a long time for it accelerate back to even an idle condition. At takeoff power, the compressor components get very hot - do a power cut the air coming in the compressor gets heated by the residual heat in the compressor. This in turn limits how fast you can add fuel in the burner without excessively back pressuring the compressor and causing a compressor stall. So it actually takes longer for the engine to accel to idle that it would during a normal (cold engine) start. The 5 seconds to 95% accel requirement referenced earlier is from a stable 'high' idle (we typically call it 'approach idle' since it's automatically selected when landing flaps are selected). Approach idle is ~10% N2 higher than the in-flight minimum idle, so that takes several more seconds. Bottom line, after initiating the Quick Windmill Relight, you're not going to have usable thrust for at least 30 seconds - probably closer to 60 seconds.
For all the complaining about this preliminary report, it actually goes into more detail than is typical.
BTW, my money is still on the 'muscle memory/action slip' or whatever you want to call it. I can easily imagine a scenario along the line of 'why did you turn off the fuel' - 'I didn't - oh wait - oh
...
July 13, 2025, 22:58:00 GMT
permalink Post: 11921757
While this is thread is still deeply into hamster wheel status, there are some valuable inputs being made. I'll try to continue with that...
Thrust lever position post-accident - it takes very little force to move the thrust levers, a little more than one pound-force at the knob. I'd be very surprised if the post impact position was the same as pre-impact (and lever angle is recorded on the FDR, so the investigators know where they were). In short - the post-accident lever position is not meaningful.
Fuel condition switch position detents - if the Indian investigators had any reason to believe that a failed or inoperative detent was a contributing fact, the authorities would have ordered a fleet-wide inspection (especially since it literally takes only seconds to do the inspection - the paperwork would take many times longer than the actual inspection).
Engine restart (i.e. "Quick Windmill Relight"): Even if the igniters were firing, at high power they won't actually spark (the electrical resistance or the air at several hundred psi prevents a spark) - so they won't spark until you get down somewhere near idle if you're close to sea level. Once the engine has dropped below the min idle, it takes a long time for it accelerate back to even an idle condition. At takeoff power, the compressor components get very hot - do a power cut the air coming in the compressor gets heated by the residual heat in the compressor. This in turn limits how fast you can add fuel in the burner without excessively back pressuring the compressor and causing a compressor stall. So it actually takes longer for the engine to accel to idle that it would during a normal (cold engine) start. The 5 seconds to 95% accel requirement referenced earlier is from a stable 'high' idle (we typically call it 'approach idle' since it's automatically selected when landing flaps are selected). Approach idle is ~10% N2 higher than the in-flight minimum idle, so that takes several more seconds. Bottom line, after initiating the Quick Windmill Relight, you're not going to have usable thrust for at least 30 seconds - probably closer to 60 seconds.
For all the complaining about this preliminary report, it actually goes into more detail than is typical.
BTW, my money is still on the 'muscle memory/action slip' or whatever you want to call it. I can easily imagine a scenario along the line of 'why did you turn off the fuel' - 'I didn't - oh wait - oh
...
Thrust lever position post-accident - it takes very little force to move the thrust levers, a little more than one pound-force at the knob. I'd be very surprised if the post impact position was the same as pre-impact (and lever angle is recorded on the FDR, so the investigators know where they were). In short - the post-accident lever position is not meaningful.
Fuel condition switch position detents - if the Indian investigators had any reason to believe that a failed or inoperative detent was a contributing fact, the authorities would have ordered a fleet-wide inspection (especially since it literally takes only seconds to do the inspection - the paperwork would take many times longer than the actual inspection).
Engine restart (i.e. "Quick Windmill Relight"): Even if the igniters were firing, at high power they won't actually spark (the electrical resistance or the air at several hundred psi prevents a spark) - so they won't spark until you get down somewhere near idle if you're close to sea level. Once the engine has dropped below the min idle, it takes a long time for it accelerate back to even an idle condition. At takeoff power, the compressor components get very hot - do a power cut the air coming in the compressor gets heated by the residual heat in the compressor. This in turn limits how fast you can add fuel in the burner without excessively back pressuring the compressor and causing a compressor stall. So it actually takes longer for the engine to accel to idle that it would during a normal (cold engine) start. The 5 seconds to 95% accel requirement referenced earlier is from a stable 'high' idle (we typically call it 'approach idle' since it's automatically selected when landing flaps are selected). Approach idle is ~10% N2 higher than the in-flight minimum idle, so that takes several more seconds. Bottom line, after initiating the Quick Windmill Relight, you're not going to have usable thrust for at least 30 seconds - probably closer to 60 seconds.
For all the complaining about this preliminary report, it actually goes into more detail than is typical.
BTW, my money is still on the 'muscle memory/action slip' or whatever you want to call it. I can easily imagine a scenario along the line of 'why did you turn off the fuel' - 'I didn't - oh wait - oh
...
The EAFR data revealed that the thrust levers remained
forward (takeoff thrust) until the impact.
Would that position be consistent with a restart attempt?
July 13, 2025, 23:43:00 GMT
permalink Post: 11921782
Thank you for your reply! I'm aware you know more about ADS-B than I do, and I'm happy to learn.
As you know, I'm referring to the map view and data on https://www.flightradar24.com/blog/f...rom-ahmedabad/ .
That's what I thought at first, based on the time stamps.
08:08:50.87 last full ADS-B message (172 kts)
08:08:54 APU inlet door starts to open, per the report.
My problem here is that the report also says that the maximum speed was 180 knots IAS at about 08:08:42. And we have
2025-06-12T08:08:46.550875Z,8005ec,23.069138,72.625871,575
associated with 184 kts as the first ADS-B message in the sequence.
Given that the clocks of ADS-B receivers are sometimes off, I think this might actually represent the moment of maximum speed; but then the AFS-B clock would be 4 seconds fast.
And that's why I adjusted my times.
A way to cross-check would be to track the aircraft position over time from the point of rotation, or to use the new photo in the report that shows the RAT over the runway to triangulate where that was.
Yes.
Would low pressure and high temperature make IAS lower than ground speed, even with the 7 knot headwind?
Either way, if they were decelerating at approximately 3 knots per second, then they would've ended up at about 150 knots IAS, which is less than Vr.
When I look at the CCTV video, 13 seconds into the flight, the aircraft is just "over the hump" and starts descending, so that tracks.
At this point, I don't know what having the engines spool up instead of being dead weight would've done to that flight path; and how successfully the aircraft could've been recovered from that.
Maybe they had only 4 seconds to flip those switches, instead of 5 seconds?
Still, the best bet is to not ask questions, but flip these switches back ASAP, no?
As you know, I'm referring to the map view and data on https://www.flightradar24.com/blog/f...rom-ahmedabad/ .
That's what I thought at first, based on the time stamps.
08:08:50.87 last full ADS-B message (172 kts)
08:08:54 APU inlet door starts to open, per the report.
My problem here is that the report also says that the maximum speed was 180 knots IAS at about 08:08:42. And we have
2025-06-12T08:08:46.550875Z,8005ec,23.069138,72.625871,575
associated with 184 kts as the first ADS-B message in the sequence.
Given that the clocks of ADS-B receivers are sometimes off, I think this might actually represent the moment of maximum speed; but then the AFS-B clock would be 4 seconds fast.
And that's why I adjusted my times.
A way to cross-check would be to track the aircraft position over time from the point of rotation, or to use the new photo in the report that shows the RAT over the runway to triangulate where that was.
Yes.
Would low pressure and high temperature make IAS lower than ground speed, even with the 7 knot headwind?
Either way, if they were decelerating at approximately 3 knots per second, then they would've ended up at about 150 knots IAS, which is less than Vr.
When I look at the CCTV video, 13 seconds into the flight, the aircraft is just "over the hump" and starts descending, so that tracks.
At this point, I don't know what having the engines spool up instead of being dead weight would've done to that flight path; and how successfully the aircraft could've been recovered from that.
Maybe they had only 4 seconds to flip those switches, instead of 5 seconds?
Still, the best bet is to not ask questions, but flip these switches back ASAP, no?
July 14, 2025, 00:26:00 GMT
permalink Post: 11921800
Did Captain cut fuel, get challenged by FO, and then fuel turned back on too late?
Or did Captain cut fuel, accuse FO to get it on the record, and then fuel turned back on too late?
If FO cut fuel, would expect a more assertive comment and faster intervention.
Or did Captain cut fuel, accuse FO to get it on the record, and then fuel turned back on too late?
If FO cut fuel, would expect a more assertive comment and faster intervention.
For me the prelim report just reveals an unintended consequence of relying on muscle memory to carry out an action that has been performed multiple times without confirmation. It happens a lot but rarely with such a tragic consequence. I have turned the ignition switch to Normal during an engine start when asked to set the park brake during a pushback. There have been multiple occasions where an A320 park brake was set when a flap setting was commanded. On more than one occasion the flaps have been raised when "gear up" was commanded. This may not have been the first time the FCO switches have been selected but definitely the first time it wasn't picked up early enough to reverse the action.
As to the CVR recordings, I will repeat what I have often stated previously. There is no inherent right of the public to receive a full transcript of the CVR in order for them to form their own opinion of what happened. It is up to the Indian AAIB to conduct an investigation under the requirements of Annex 13 and possibly a fuller transcript of the CVR will be published in the Final Report to help the reader gain an understanding of what happened.
My belief is that CVideoRs, with robust protections and legislation around their use, will help accident investigations immensely by answering some of the what questions that the FDR and CVR don't seem able to. It doesn't have to be set up like the many Go-Pro images that are on social media. All that is needed is an image of the center console and the engine display and EICAS/ECAM screens .There would be no need to have images of the pilots faces.
July 14, 2025, 00:33:00 GMT
permalink Post: 11921803
While this is thread is still deeply into hamster wheel status, there are some valuable inputs being made. I'll try to continue with that...
Thrust lever position post-accident - it takes very little force to move the thrust levers, a little more than one pound-force at the knob. I'd be very surprised if the post impact position was the same as pre-impact (and lever angle is recorded on the FDR, so the investigators know where they were). In short - the post-accident lever position is not meaningful.
Fuel condition switch position detents - if the Indian investigators had any reason to believe that a failed or inoperative detent was a contributing fact, the authorities would have ordered a fleet-wide inspection (especially since it literally takes only seconds to do the inspection - the paperwork would take many times longer than the actual inspection).
Engine restart (i.e. "Quick Windmill Relight"): Even if the igniters were firing, at high power they won't actually spark (the electrical resistance or the air at several hundred psi prevents a spark) - so they won't spark until you get down somewhere near idle if you're close to sea level. Once the engine has dropped below the min idle, it takes a long time for it accelerate back to even an idle condition. At takeoff power, the compressor components get very hot - do a power cut the air coming in the compressor gets heated by the residual heat in the compressor. This in turn limits how fast you can add fuel in the burner without excessively back pressuring the compressor and causing a compressor stall. So it actually takes longer for the engine to accel to idle that it would during a normal (cold engine) start. The 5 seconds to 95% accel requirement referenced earlier is from a stable 'high' idle (we typically call it 'approach idle' since it's automatically selected when landing flaps are selected). Approach idle is ~10% N2 higher than the in-flight minimum idle, so that takes several more seconds. Bottom line, after initiating the Quick Windmill Relight, you're not going to have usable thrust for at least 30 seconds - probably closer to 60 seconds.
For all the complaining about this preliminary report, it actually goes into more detail than is typical.
BTW, my money is still on the 'muscle memory/action slip' or whatever you want to call it. I can easily imagine a scenario along the line of 'why did you turn off the fuel' - 'I didn't - oh wait - oh
...
Thrust lever position post-accident - it takes very little force to move the thrust levers, a little more than one pound-force at the knob. I'd be very surprised if the post impact position was the same as pre-impact (and lever angle is recorded on the FDR, so the investigators know where they were). In short - the post-accident lever position is not meaningful.
Fuel condition switch position detents - if the Indian investigators had any reason to believe that a failed or inoperative detent was a contributing fact, the authorities would have ordered a fleet-wide inspection (especially since it literally takes only seconds to do the inspection - the paperwork would take many times longer than the actual inspection).
Engine restart (i.e. "Quick Windmill Relight"): Even if the igniters were firing, at high power they won't actually spark (the electrical resistance or the air at several hundred psi prevents a spark) - so they won't spark until you get down somewhere near idle if you're close to sea level. Once the engine has dropped below the min idle, it takes a long time for it accelerate back to even an idle condition. At takeoff power, the compressor components get very hot - do a power cut the air coming in the compressor gets heated by the residual heat in the compressor. This in turn limits how fast you can add fuel in the burner without excessively back pressuring the compressor and causing a compressor stall. So it actually takes longer for the engine to accel to idle that it would during a normal (cold engine) start. The 5 seconds to 95% accel requirement referenced earlier is from a stable 'high' idle (we typically call it 'approach idle' since it's automatically selected when landing flaps are selected). Approach idle is ~10% N2 higher than the in-flight minimum idle, so that takes several more seconds. Bottom line, after initiating the Quick Windmill Relight, you're not going to have usable thrust for at least 30 seconds - probably closer to 60 seconds.
For all the complaining about this preliminary report, it actually goes into more detail than is typical.
BTW, my money is still on the 'muscle memory/action slip' or whatever you want to call it. I can easily imagine a scenario along the line of 'why did you turn off the fuel' - 'I didn't - oh wait - oh
...
The last line, is not a zero possibility, but at present the whole wiring system for the fuel control switches would need to be evaluated for any potential common fault that may be intermittent before I would lean towards the cognitive slip type error. The poor old FO would have both hands on the yoke from V1, irrespective of the company's SOP and so would have been rather unpleasantly surprised by the loss of performance. I think the 10 seconds in this case is remarkably fast observation-orientation-decision-action sequence, and that one engine had already started to recover towards operation is a credit to the design of the engine.
July 14, 2025, 00:38:00 GMT
permalink Post: 11921804
Based on the news coming out of India, it appears that your suspicions regarding malicious intent may well be correct, but it is not the younger FO under suspicion as your post seems to suggest but the older more experienced captain. Other comments in this thread had already made me think that the younger pilot was the PF and that it was he who had challenged the PM because he would have been focused on flying the aircraft and would have had neither the time nor the inclination to adjust the critical fuel cut off switches which you yourself categorically claim would never be mistaken for other switches.
July 14, 2025, 01:01:00 GMT
permalink Post: 11921815
For me the prelim report just reveals an unintended consequence of relying on muscle memory to carry out an action that has been performed multiple times without confirmation. It happens a lot but rarely with such a tragic consequence. I have turned the ignition switch to Normal during an engine start when asked to set the park brake during a pushback. There have been multiple occasions where an A320 park brake was set when a flap setting was commanded. On more than one occasion the flaps have been raised when "gear up" was commanded. This may not have been the first time the FCO switches have been selected but definitely the first time it wasn't picked up early enough to reverse the action.
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When running a sim, on repo', setup or end of session I never let any candidate push any buttons or do any actions that would not be considered not part of a normal flow that would normally be conducted at that point. On a reposition to a threshold, I might get the candidate to cycle the FDs or LSK in the MCDU once we are lined up and visuals back but that's about it. Everything else, start lever reengagement, flap resets etc are all off limits to the candidate and I brief as such.
Furthermore when I do the odd simulator in seat instruction exercise and do OEM prescribed "non normal" training (like a "gear up" -> Flap react incorrect selection) I will clench my non operating hand or squeeze my toes until they hurt and consciously tell myself I am about to do something incorrect... then do the (incorrect) action. That is my way of - hopefully - preventing muscle memory habits.
Last edited by compressor stall; 14th July 2025 at 01:35 .