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.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): EFATO Generators/Alternators Takeoff Roll V1 V2
July 09, 2025, 11:32:00 GMT
permalink Post: 11918322
If the data does show "movement" of the switches, hopefully it will only be the rapid cycling mentioned by Ferret.
Subjects: None
July 11, 2025, 22:16:00 GMT
permalink Post: 11919894
From the report, there is no indicated time stamp identifying the point when one pilot asked the other "why did you cut off"
This could explain the the assumption that it took ten seconds to reverse the switch positions.
Cut off could have been noticed at any point later than 08:08:42 but before 08:08:52.
This could explain the the assumption that it took ten seconds to reverse the switch positions.
Cut off could have been noticed at any point later than 08:08:42 but before 08:08:52.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Fuel (All) Fuel Cutoff Switches Pilot "Why did you cut off" Preliminary Report Timeline (Preliminary Report)
July 13, 2025, 13:25:00 GMT
permalink Post: 11921321
I still think that one of the most puzzling things from the Preliminary Report is the 4 second gap between Engine 1 fuel cutoff switch being returned to RUN, and that of Engine 2. It seems generally agreed one second is a reasonable time to operate both switches, so why did it take so long to move the 2nd switch?
I'm not implicating either pilot, without more evidence.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Fuel (All) Fuel Cutoff Fuel Cutoff Switches Preliminary Report RUN/CUTOFF
July 13, 2025, 18:13:00 GMT
permalink Post: 11921506
I'd assume that the prelim wouldnt (surely?) call out the gear down item explicitly and not reference a command for gear up if it existed - but could be wrong. For me your former suggestion is more likely I think.
Incidentally, on the topic of lever positions in the wreckage, anyone find the thrust position at idle in the wreckage (at odds with the data) of interest? My assumption is this must have happened post impact, but it's a (small) oddity.
Incidentally, on the topic of lever positions in the wreckage, anyone find the thrust position at idle in the wreckage (at odds with the data) of interest? My assumption is this must have happened post impact, but it's a (small) oddity.
Subjects: None
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?
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): EAFR FDR Fuel (All) Fuel Cutoff Switches Fuel Cutoff Switches (detent) Preliminary Report Quick Windmill Relight Relight
July 14, 2025, 00:06:00 GMT
permalink Post: 11921794
It doesn't really matter - the FADEC will do it's best to get the engine running again regardless of the lever position - in that regard the only real difference is once the engine reaches min idle, it'll simply keep accelerating to the target N1 (or EPR). There is no need to move the thrust lever to idle to get a successful start.
There have been a few cases that I know about where the flight crew did a normal ground start with the thrust lever at mid-power, and the engine simply continues to accelerate to the 'commanded' N1 or EPR. In one case (a 777), this happened during pushback. As the engine continued to accelerate above idle, the thrust caused the aircraft to jackknife around the tug, causing the tug driver to have to dive for cover to prevent serious injury. That even happened while we were doing the development of the 747-8 - it prompted me to ask the 747 Chief Pilot if we wanted to consider a 'start inhibit' in the FADEC logic that would prevent a ground start attempt if the thrust lever wasn't at idle (ground starts only - for what should be obvious reasons). He didn't like the idea, and it went no further...
There have been a few cases that I know about where the flight crew did a normal ground start with the thrust lever at mid-power, and the engine simply continues to accelerate to the 'commanded' N1 or EPR. In one case (a 777), this happened during pushback. As the engine continued to accelerate above idle, the thrust caused the aircraft to jackknife around the tug, causing the tug driver to have to dive for cover to prevent serious injury. That even happened while we were doing the development of the 747-8 - it prompted me to ask the 747 Chief Pilot if we wanted to consider a 'start inhibit' in the FADEC logic that would prevent a ground start attempt if the thrust lever wasn't at idle (ground starts only - for what should be obvious reasons). He didn't like the idea, and it went no further...
Thanks, makes sense. It was the above note that confused me.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): FADEC
July 16, 2025, 18:18:00 GMT
permalink Post: 11923902
It was stated that Air India didn't bother to do so, as the directive or whatever it's called, was not mandatory.
I'm not trying to point the finger at Air India, or suggest that these switches could be faulty, rather highlight how the industry can be seen to function.
There have been numerous accidents that could have been prevented, if remedial actions had not been allowed to be deferred.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Fuel (All) Fuel Cutoff Switches Special Airworthiness Information Bulletin