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| ignorantAndroid
June 21, 2025, 18:02:00 GMT permalink Post: 11907949 |
Another post referenced the RAT only supplying electrical power after 10s - I find that hard to believe, not instant obviously because there has to be some stabilisation time and startup/boot time but it would imply the LH flight instruments would only be active very late. Hopefully the RAT hydraulics would be effective quicker than that.
The engine-driven hydraulic pumps should still work for at least a few seconds after flameout. There's also a small amount of stored energy in the hydraulic systems even after the pumps stop. So even with that 6-second delay for the RAT, there shouldn't be any significant interruption in hydraulic power for the primary flight controls. |
| TURIN
July 01, 2025, 08:49:00 GMT permalink Post: 11914118 |
In my experience the APU supplies enough power to run all systems. Hydraulic pumps, fuel pumps etc |
| Sailvi767
July 01, 2025, 12:39:00 GMT permalink Post: 11914246 |
On the 767, 757 and A330 anytime you are in single generator operations the aircraft is load shedding. The 787 with a totally different electrical system might function differently.
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| Engineless
July 11, 2025, 20:40:00 GMT permalink Post: 11919772 |
The aircraft achieved the maximum recorded airspeed of 180 Knots IAS at about 08:08:42
UTC and immediately thereafter, the Engine 1 and Engine 2 fuel cutoff switches transitioned from RUN to CUTOFF position one after another with a time gap of 01 sec. The Engine N1 and N2 began to decrease from their take-off values as the fuel supply to the engines was cut off. In the cockpit voice recording, one of the pilots is heard asking the other why did he cutoff. The other pilot responded that he did not do so. The CCTV footage obtained from the airport showed Ram Air Turbine (RAT) getting deployed during the initial climb immediately after lift-off (fig. 15). No significant bird activity is observed in the vicinity of the flight path. The aircraft started to lose altitude before crossing the airport perimeter wall. As per the EAFR, the Engine 1 fuel cutoff switch transitioned from CUTOFF to RUN at about 08:08:52 UTC. The APU Inlet Door began opening at about 08:08:54 UTC, consistent with the APU Auto Start logic. Thereafter at 08:08:56 UTC the Engine 2 fuel cutoff switch also transitions from CUTOFF to RUN. When fuel control switches are moved from CUTOFF to RUN while the aircraft is inflight, each engines full authority dual engine control (FADEC) automatically manages a relight and thrust recovery sequence of ignition and fuel introduction. The EGT was observed to be rising for both engines indicating relight. Engine 1’s core deceleration stopped, reversed and started to progress to recovery. Engine 2 was able to relight but could not arrest core speed deceleration and re-introduced fuel repeatedly to increase core speed acceleration and recovery. The EAFR recording stopped at 08:09:11 UTC As per the EAFR data both engines N2 values passed below minimum idle speed, and the RAT hydraulic pump began supplying hydraulic power at about 08:08:47 UTC. RAT in extended position 15 As per the EAFR, the Engine 1 fuel cutoff switch transitioned from CUTOFF to RUN at about 08:08:52 UTC. The APU Inlet Door began opening at about 08:08:54 UTC, consistent with the APU Auto Start logic. Thereafter at 08:08:56 UTC the Engine 2 fuel cutoff switch also transitions from CUTOFF to RUN. When fuel control switches are moved from CUTOFF to RUN while the aircraft is inflight, each engines full authority dual engine control (FADEC) automatically manages a relight and thrust recovery sequence of ignition and fuel introduction. The EGT was observed to be rising for both engines indicating relight. Engine 1’s core deceleration stopped, reversed and started to progress to recovery. Engine 2 was able to relight but could not arrest core speed deceleration and re-introduced fuel repeatedly to increase core speed acceleration and recovery. The EAFR recording stopped at 08:09:11 UTC At about 08:09:05 UTC, one of the pilots transmitted “MAYDAY MAYDAY MAYDAY”. 08:08:42 Engine 1 and Engine 2 fuel cutoff switches transitioned from RUN to CUTOFF position. One of the pilots asks the other why did he cutoff. The other pilot responded that he did not do so. 08:08:52 Engine 1 fuel cutoff switch transitioned from CUTOFF to RUN 08:08:56 Engine 2 fuel cutoff switch also transitions from CUTOFF to RUN Who (or what?) operated the cutoff switches? Last edited by Engineless; 11th July 2025 at 20:53 . |
| appruser
July 12, 2025, 01:28:00 GMT permalink Post: 11920070 |
Can someone with the engineering knowledge build a timeline/timeframe for fuel cutoff switch RUN to CUTOFF -> fuel stops -> engine flameout -> N2 drops to ? -> VFSGs quit -> RAT deployment starts -> RAT full power -> APU deployment start?
Does the RAT really start providing power in 4 seconds from the E2 fuel cutoff switch RUN -> CUTOFF? Timeline from AAIB and the public CCTV video: 08:08:33 v1 153 kts . 08:08:35 vr 155 kts . . . 08:08:39 Liftoff, A/G Air Mode, rotation at 00:18 in public CCTV video . . 08:08:42 E1 Fuel Cutoff Switch RUN -> CUTOFF, 180 kts 08:08:43 E2 Fuel Cutoff Switch RUN -> CUTOFF .............? N1 N2 begin to decrease .............? "Why did you cutoff", "I didn't" .............? Airport CCTV shows RAT .............? N2 < idle speed 08:08:47 RAT hydraulic power . 08:08:49 Public CCTV video: visible loss of thrust, Alt < 200ft using wingspan . . 08:08:52 E1 Fuel Cutoff Switch CUTOFF -> RUN, CCTV video: visible descent . 08:08:54 APU inlet door begins opening . 08:08:56 E2 Fuel Cutoff Switch CUTOFF -> RUN 08:09:05 MAYDAY 08:09:11 EAFR Recording stops 08:14:44 Crash Fire Tender leaves airport Last edited by appruser; 12th July 2025 at 01:29 . Reason: readability |
| Musician
July 12, 2025, 08:56:00 GMT permalink Post: 11920377 |
Was the RAT deployed manually?
The report says,
As per the EAFR data both engines N2 values passed below minimum idle speed, and the
RAT hydraulic pump began supplying hydraulic power at about 08:08:47 UTC.
This was 5 seconds after the fuel was cut off.
It suggests to me that the RAT deployment was initiated while the engines were still above idle and generating electrical power. Obviously one of the pilots could have done it via depressing the switch, as it's a "dual engine failure/stall" memory item (see Air India Ahmedabad accident 12th June 2025 Part 2 ) that won't hurt anything. Is there a way for the RAT to deploy while the engines are still above idle? |
| nachtmusak
July 12, 2025, 10:43:00 GMT permalink Post: 11920474 |
SLF: I have a small observation but I'm not sure what it means or if it has any relevance to the accident.
Previously I had assumed that the ADS-B data cut out at the same time as power was lost, so I imagined that whatever caused the fairly clear loss of thrust would have happened not too long before. But this report throws a bit of a wrench in my understanding of that. According to the report, the fuel cutoff switches transition from RUN to CUTOFF at or very shortly after 08:08:42 UTC. Both engines' N2 values pass below minimum idle speed and the RAT begins supplying hydraulic power at about 08:08:47. Does this not imply that the generators have already been lost? With the APU also being off (the APU inlet door is noted to start opening at 08:08:54), I would have expected ADS-B data to cut out at or before 08:08:47. But curiously FlightRadar24 at least claims to have received data frames from the aircraft until 08:08:51.640970, almost five seconds later and almost ten seconds after the transition to CUTOFF (though the last frame containing coordinates comes at 08:08:50.871005). Could anyone with relevant experience confirm how long it would take for AC power to be lost in this situation? Also, is it usual/unusual for a preliminary report like this to mention if/when the flight recorder switched to its independent power supply? I imagine it would definitely be in the final report, but I'd hoped it would be easily observable enough to be in this one. Beyond idle curiosity I'm asking because the report also says the no. 1 engine's cutoff switch transitioned from CUTOFF to RUN at "about 08:08:52", which oddly coincides with the last ADS-B data frame at 08:08:51.640970, and that seems important somehow. Or more likely I'm just ignorant of some quirk of the 787's electrical system. For reference FR24's CSV containing all ADS-B frames supposedly received from the aircraft can be found in their post here: https://www.flightradar24.com/blog/f...rom-ahmedabad/ |
| Someone Somewhere
July 12, 2025, 11:02:00 GMT permalink Post: 11920495 |
The accident aircraft was written up for a status message of ”STAB POS XDCR” on the previous flight, which is a message relating to implausible data from the stab trim switches. It was released from maintenance (according to the preliminary report) at 06:40UTC ahead of an 07:40UTC departure (the crash flight) with ”no fault found”.
On the 787-8, as all modern planes, switches are not cabled as dry closing contacts all the way from the switch poles to the affected end devices (FADECs in the case of fuel cutoff switches), but rather connect locally to an analogue/digital converter to encode the switch position data onto the digital comms bus ARINC629 which allows all aircraft systems to talk to one another. Are the fuel cutoff switches, which are positioned adjacent to the stab trim switches, connected to the same ADC module which produced the error message on the previous flight, which maintenance was unable to resolve before the accident flight took off? I do not know, but it must be worthy of being looked into. I think they're called remote data concentrators - in many cases it is a conversion from a direct digital input to a bus signal; electronics would not call it an 'analog' input unless it was actually measuring a quantitative value.
Was the RAT deployed manually?
The report says, As per the EAFR data both engines N2 values passed below minimum idle speed, and the RAT hydraulic pump began supplying hydraulic power at about 08:08:47 UTC. This was 5 seconds after the fuel was cut off. It suggests to me that the RAT deployment was initiated while the engines were still above idle and generating electrical power. Obviously one of the pilots could have done it via depressing the switch, as it's a "dual engine failure/stall" memory item (see Air India Ahmedabad accident 12th June 2025 Part 2 ) that won't hurt anything. Is there a way for the RAT to deploy while the engines are still above idle? That is a very good question IMHO. |
| Sailvi767
July 12, 2025, 11:46:00 GMT permalink Post: 11920554 |
Was the RAT deployed manually?
The report says,
As per the EAFR data both engines N2 values passed below minimum idle speed, and the
RAT hydraulic pump began supplying hydraulic power at about 08:08:47 UTC.
This was 5 seconds after the fuel was cut off.
It suggests to me that the RAT deployment was initiated while the engines were still above idle and generating electrical power. Obviously one of the pilots could have done it via depressing the switch, as it's a "dual engine failure/stall" memory item (see Air India Ahmedabad accident 12th June 2025 Part 2 ) that won't hurt anything. Is there a way for the RAT to deploy while the engines are still above idle? |
| Musician
July 13, 2025, 07:18:00 GMT permalink Post: 11921078 |
The Action Slip scenario
What is an action slip?
There's a possible scenario we're discussing here that fits all of the available evidence. It proposes that one of the pilots operated the switches in an unconscious action called an "action slip". This is a rote action that we do without conscious thought when we're distracted: we mean to do something, and then we get our signals crossed and do something else. To learn more, search for "action slip" or "cerebellum" on this thread; I hope paulross adds the keyword to the next build of his excellent index at https://paulross.github.io/pprune-th...171/index.html . How would this scenario play out? We don't have enough evidence to pin down the exact sequence, so there are some assumptions here that I hope you find plausible. (And obviously it's not the only scenario that fits the evidence.) We especially do not know who did what and why, so that is all guesswork on my part. The times are taken from the preliminary report. The report places the verbal exchange among the pilots where I put it. ——— 8:08:39 The 787 becomes airborne. The F/O is pilot flying (PF), with both hands on the yoke. The Captain is PNF (not flying). 8:08:42 The PNF unconsciously flips both fuel switches to CUT OFF, one after the other. This is a rote action performed after each flight, or as training captain in the simulator. The action cuts power to the engines; they stop delivering thrust almost immediately, and the turbines start slowing down. The 787 systems disconnect the electrical generators in advance of them failing. The right side The PF feels the cessation of thrust. He looks at the display to see an ENGINES SHUT OFF message. He assumes the PNF shut them off, and asks him why he shut them off. This is the lowest "probe" level on the PACE assertiveness scale; see e.g. https://psychsafety.com/pace-graded-assertiveness/ or search for "probe alert" on pprune if you wish to know more. The highest level of assertiveness, E for "emergency", would have the F/O put the switches back himself immediately, but that would have required a high degree of confidence in the face of the older Captain that may have been difficult to achieve. Since the action was unconscious, the PNF replies that he did not do that. 8:08:47 The RAT starts delivering hydraulic power, the engines decelerate past idle. The PNF realizes that engine power is in fact cut. Eventually he checks the switches he thinks he did not touch, sees the engine 1 switch first and flips it back to RUN at 8:08:52. He then thinks to check the second switch and flips it up at 8:08:56. The accident sequence ensues. There's really not much the PNF can do at this point. At 8:09:05, he transmits a MAYDAY. ——— Obviously there are variations to this, for example it could have been the PF who put the fuel switches back. (In the above scenario, the PF is focused on flying—aviate!—and never turns his head to see the switches.) My goal was simply to set out a possible sequence, to see whether it feels plausible. Remember, as you see other scenarios put forth, that any issues a person could wrestle with would also be distracting. While both pilots would be very focused during the takeoff run, the moment the aircraft lifted off, the PNF could well have mentally relaxed a little, opening an opportunity for the action slip. Thoughts? Edit: I got the roles mixed up; in a fixed scenario, either the Captain was the PF (and may have set the switches to cutoff), or flight control changed over at the power failure. Last edited by Musician; 13th July 2025 at 08:03 . |
| Speed_Trim_Fail
July 13, 2025, 07:36:00 GMT permalink Post: 11921087 |
What is an action slip?
There's a possible scenario we're discussing here that fits all of the available evidence. It proposes that one of the pilots operated the switches in an unconscious action called an "action slip". This is a rote action that we do without conscious thought when we're distracted: we mean to do something, and then we get our signals crossed and do something else. To learn more, search for "action slip" or "cerebellum" on this thread; I hope paulross adds the keyword to the next build of his excellent index at https://paulross.github.io/pprune-th...171/index.html . How would this scenario play out? We don't have enough evidence to pin down the exact sequence, so there are some assumptions here that I hope you find plausible. (And obviously it's not the only scenario that fits the evidence.) We especially do not know who did what and why, so that is all guesswork on my part. The times are taken from the preliminary report. The report places the verbal exchange among the pilots where I put it. \x97\x97\x97 8:08:39 The 787 becomes airborne. The F/O is pilot flying (PF), with both hands on the yoke. The Captain is PNF (not flying). 8:08:42 The PNF unconsciously flicks both fuel switches to CUT OFF, one after the other. This is a rote action performed after each flight, or as training captain in the simulator. The action cuts power to the engines; they stop delivering thrust almost immediately, and the turbines start slowing down. The 787 systems disconnect the electrical generators in advance of them failing. The right side (Captain's side) of the cockpit loses power to most instruments. With all 4 generators offline, the RAT deploys to provide emergency power. The PF feels the cessation of thrust. He looks at the display to see an ENGINES SHUT OFF message. He assumes the PNF shut them off, and asks him why he shut them off. This is the lowest "probe" level on the PACE assertiveness scale; see e.g. https://psychsafety.com/pace-graded-assertiveness/ or search for "probe alert" on pprune if you wish to know more. The highest level of assertiveness, E for "emergency", would have the F/O put the switches back himself immediately, but that would have required a high degree of confidence in the face of the older Captain that may have been difficult to achieve. Since the action was unconscious, the PNF replies that he did not do that. 8:08:47 The RAT starts delivering hydraulic power, the engines decelerate past idle. The PNF realizes that engine power is in fact cut. Eventually he checks the switches he thinks he did not touch, sees the engine 1 switch first and flips it back to RUN at 8:08:52. He then thinks to check the second switch and flips it up at 8:08:56. The accident sequence ensues. There's really not much the PNF can do at this point. At 8:09:05, he transmits a MAYDAY. \x97\x97\x97 Obviously there are variations to this, for example it could have been the PF who put the fuel switches back. (In the above scenario, the PF is focused on flying\x97aviate!\x97and never turns his head to see the switches.) My goal was simply to set out a possible sequence, to see whether it feels plausible. Remember, as you see other scenarios put forth, that any issues a person could wrestle with would also be distracting. While both pilots would be very focused during the takeoff run, the moment the aircraft lifted off, the PNF could well have mentally relaxed a little, opening an opportunity for the action slip. Thoughts? |
| CharlieMike
July 13, 2025, 07:41:00 GMT permalink Post: 11921093 |
What is an action slip?
There's a possible scenario we're discussing here that fits all of the available evidence. It proposes that one of the pilots operated the switches in an unconscious action called an "action slip". This is a rote action that we do without conscious thought when we're distracted: we mean to do something, and then we get our signals crossed and do something else. To learn more, search for "action slip" or "cerebellum" on this thread; I hope paulross adds the keyword to the next build of his excellent index at https://paulross.github.io/pprune-th...171/index.html . How would this scenario play out? We don't have enough evidence to pin down the exact sequence, so there are some assumptions here that I hope you find plausible. (And obviously it's not the only scenario that fits the evidence.) We especially do not know who did what and why, so that is all guesswork on my part. The times are taken from the preliminary report. The report places the verbal exchange among the pilots where I put it. ——— 8:08:39 The 787 becomes airborne. The F/O is pilot flying (PF), with both hands on the yoke. The Captain is PNF (not flying). 8:08:42 The PNF unconsciously flicks both fuel switches to CUT OFF, one after the other. This is a rote action performed after each flight, or as training captain in the simulator. The action cuts power to the engines; they stop delivering thrust almost immediately, and the turbines start slowing down. The 787 systems disconnect the electrical generators in advance of them failing. The right side (Captain's side) of the cockpit loses power to most instruments. With all 4 generators offline, the RAT deploys to provide emergency power. The PF feels the cessation of thrust. He looks at the display to see an ENGINES SHUT OFF message. He assumes the PNF shut them off, and asks him why he shut them off. This is the lowest "probe" level on the PACE assertiveness scale; see e.g. https://psychsafety.com/pace-graded-assertiveness/ or search for "probe alert" on pprune if you wish to know more. The highest level of assertiveness, E for "emergency", would have the F/O put the switches back himself immediately, but that would have required a high degree of confidence in the face of the older Captain that may have been difficult to achieve. Since the action was unconscious, the PNF replies that he did not do that. 8:08:47 The RAT starts delivering hydraulic power, the engines decelerate past idle. The PNF realizes that engine power is in fact cut. Eventually he checks the switches he thinks he did not touch, sees the engine 1 switch first and flips it back to RUN at 8:08:52. He then thinks to check the second switch and flips it up at 8:08:56. The accident sequence ensues. There's really not much the PNF can do at this point. At 8:09:05, he transmits a MAYDAY. ——— Obviously there are variations to this, for example it could have been the PF who put the fuel switches back. (In the above scenario, the PF is focused on flying—aviate!—and never turns his head to see the switches.) My goal was simply to set out a possible sequence, to see whether it feels plausible. Remember, as you see other scenarios put forth, that any issues a person could wrestle with would also be distracting. While both pilots would be very focused during the takeoff run, the moment the aircraft lifted off, the PNF could well have mentally relaxed a little, opening an opportunity for the action slip. Thoughts? Seeing that the gear remained down after liftoff, there was CVR confusion after the event, and there was an attempt to rectify the situation…. I’m now thinking aviation is witnessing its most bizarre action-slip it’s ever seen and we’ll learn that the human automatic system is capable of making the most inappropriate and illogical responses to a given situation. I suspect fatigue and the captains sim experience of flicking switches plays a part. As a result of this, I think we’ll see a renewed interest in slowing down actions at all times…touch a control, look at it, pause, consciously think about what you are touching before you execute it. This needs to be habitual, especially on LH fleets where fatigue inevitably plays into the operation. We’ll also be discouraging the “insta-pilot” trend of showing how slick you are (usually on A320) where your hands flick round the flight deck at lightning speed. Even in more benign scenarios like shutdown flows etc, this isn’t a good habit. |
| Mrshed
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. 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) |
| B2N2
July 13, 2025, 19:06:00 GMT permalink Post: 11921541 |
These for me are very interesting questions.
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. If memory serves me right on the 777 the electrical output capacity of the APU is about 8-10 times the output capacity of the RAT. It will likely be even more on the 787. |
| Mrshed
July 13, 2025, 19:10:00 GMT permalink Post: 11921547 |
I assume this means that the APU was not operational until this point? |
| B2N2
July 13, 2025, 19:16:00 GMT permalink Post: 11921552 |
I don\x92t know if it started to open or was registered open at 8 seconds. |
| Musician
July 13, 2025, 19:18:00 GMT permalink Post: 11921555 |
The APU needs air to operate. The inlet provides that air. |
| Feathers McGraw
July 13, 2025, 19:20:00 GMT permalink Post: 11921557 |
I believe the APU can take quite a while to start, certainly more than 30 seconds. The APU inlet door in the wreckage is open but it's not clear if it is fully open or perhaps closed a little with the loss of whatever power is used to drive the actuator. Electrical or hydraulic? I have seen other 787 APU inlet door photos showing what seems to be a wider aperture but that was on an aircraft on the ground.
|
| Someone Somewhere
July 14, 2025, 08:01:00 GMT permalink Post: 11921930 |
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..
If the restriction to getting the engine relit earlier (well above idle N2) is only the spark gap, I am somewhat surprised that beefier igniters, perhaps with high/low voltage settings (for emergency/normal use), are not used. Compressed air is a reasonable insulator, but it's nowhere the oil, SF6, or vacuum that HV operators use in tight spaces. Bigger igniters might mean you can spark the fuel at ~70% N2 at which point you're presumably seconds away from having thrust again, and don't do the significant engine damage associated with I assume EGT exceedances from scheduling high fuel to ramp N2 rapidly with already-hot parts.
My final thoughts for this event.
Misinformation, most of us including myself was of the view that Gear Up had been selected because we saw an image believed to be the accident aircraft with the bogeys stowed for retraction.The report image shows that they were not and the Gear Selector was down. A crucial element in the sequence of events.
I think there is a bit of confusion running in this thread about how the auto restart function works.
Normal start uses a lot of electrical power to drive the two starters. In a situation with only the RAT supplying electrical power there won't be anywhere near enough power to turn even one starter. Restart relies on windmilling only. Igniters don't need a huge amount of power, fuel will be gravity fed to the engine driven pumps. The APU autostart function will use power from the dedicated APU battery only. Edit to add, it can take an age for the APU to start off the battery. Well over a minute. You can spin up the engines in three ways: starter motor (electric or pneumatic, depending on type), windmill (but at low speeds, the RPM given by a windmill won't be enough), or the inertia of the already spinning engine. Quick relight I believe is predominantly inertia. |
| appruser
July 15, 2025, 16:59:00 GMT permalink Post: 11923087 |
Having read through most of the posts in this and the other threads, and the preliminary report a few times in parts, am mystified by this:
The Preliminary Report states: "The CCTV footage obtained from the airport showed Ram Air Turbine (RAT) getting deployed during the initial climb immediately after lift-off (fig. 15). No significant bird activity is observed in the vicinity of the flight path. The aircraft started to lose altitude before crossing the airport perimeter wall." Does this mean the RAT deployed "immediately after" in the sense of within 1 second after lift-off? We, as a group, certainly seem to be interpreting the "immediately thereafter" in a prior paragraph to mean that the E1 and E2 fuel cutoff switches went RUN -> CUTOFF within 1 second or so after max airspeed of 180kts at 08:08:42. The prior paragraph for quick ref: "The aircraft achieved the maximum recorded airspeed of 180 Knots IAS at about 08:08:42 UTC and immediately thereafter, the Engine 1 and Engine 2 fuel cutoff switches transitioned from RUN to CUTOFF position one after another with a time gap of 01 sec. The Engine N1 and N2 began to decrease from their take-off values as the fuel supply to the engines was cut off." Additionally, have to say, this PR has a few major weaknesses in it: - no timestamp for RAT deployment, though RAT hydraulic power coming online has one; also is it for initial power or rated power? - no timestamp for the pilot conversation about 'cutoff', though it is provided for the MAYDAY. - no timestamps for E1/E2 Fuel Cutoff Switches going from RUN -> CUTOFF, though they're provided for CUTOFF -> RUN. Last edited by T28B; 15th July 2025 at 17:15 . Reason: formatting errors fixed. |
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