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Tailspin Turtle
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? |
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. |
AirScotia
July 14, 2025, 11:11:00 GMT permalink Post: 11922092 |
May I just point out that the survivor's account of what he remembered seems to have been entirely accurate?
He heard a loud bang - RAT did deploy, and does do so with a loud bang. Green and white lights came on - very likely emergency lights Aircraft seemed to be struggling for height - it was Sudden roar of an engine - we know No. 1 powered up just too late A number of us here discounted what he said because he was traumatised and, you know, just a passenger. But he wasn't wrong about anything. |
Pip_Pip
July 14, 2025, 20:36:00 GMT permalink Post: 11922482 |
The deemed position of the CCTV camera is only an estimate, based on visual cues. I'm happy to share my workings, should anyone find it useful to cross-reference this with other data they are working on, but I will avoid cluttering up the thread any further until/unless it becomes relevant. You're looking for the point where the LEFT of the two white lines intersects the runway (ignore the white dots): ![]() |
Musician
July 14, 2025, 21:36:00 GMT permalink Post: 11922527 |
This was posted sometime ago, but if anyone would still find it useful to pinpoint the location of the aircraft in the 'new' photo from the Preliminary Report (with RAT deployed) I made a crude attempt which placed it roughly midway between the two sets of identical touchdown zone markings, ~245m (803 ft) from the displaced threshold of RW05.
The deemed position of the CCTV camera is only an estimate, based on visual cues. I'm happy to share my workings, should anyone find it useful to cross-reference this with other data they are working on, but I will avoid cluttering up the thread any further until/unless it becomes relevant. You're looking for the point where the LEFT of the two white lines intersects the runway (ignore the white dots): |
GroundedSpanner
July 14, 2025, 21:47:00 GMT permalink Post: 11922533 |
I cant speak for how long it would take to connect the dots though. |
Pip_Pip
July 14, 2025, 22:05:00 GMT permalink Post: 11922543 |
I figure you are already well aware of the following, but I mention it to avoid others reading more into the words than was intended: the report doesn't confirm whether or not the CCTV still in Figure 15 is the first frame where the RAT can be seen fully deployed. |
D Bru
July 14, 2025, 22:27:00 GMT permalink Post: 11922550 |
Switching off the engines would cut power. (the RAT deployed before they overflew the end of the runway) The HUD would go blank. As would most of the display units. The lighting would change. The hissing of conditioned air would stop. Various 'noises' would cease. The engines sound would change dramatically, and they would feel the deceleration. The one EICAS screen remaining would be generating all sorts of messages. It would be obvious that power was lost.
I cant speak for how long it would take to connect the dots though. https://data.ntsb.gov/Docket/Documen...man-Master.PDF ) ![]() ![]() Last edited by D Bru; 14th July 2025 at 22:39 . |
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. |
appruser
July 15, 2025, 17:40:00 GMT permalink Post: 11923111 |
Since the preliminary report neglected including when the RAT deployment occurred, I've tried to estimate it based on the picture they did include:
![]() Baro altitude should be around 150ft; using the public cctv video, I estimate this picture was taken between 4-7 seconds after rotation. A wide range, but that was the best estimate I could come up with. Maybe someone else could narrow it down further. |
Xeptu
July 16, 2025, 00:30:00 GMT permalink Post: 11923360 |
Since the preliminary report neglected including when the RAT deployment occurred, I've tried to estimate it based on the picture they did include:
![]() Baro altitude should be around 150ft; using the public cctv video, I estimate this picture was taken between 4-7 seconds after rotation. A wide range, but that was the best estimate I could come up with. Maybe someone else could narrow it down further. I'm equally impressed by how quickly No1 engine recovered. I think it's safe to say that this situation is not recoverable, but a truly impressive piece of engineering all the same. |
appruser
July 16, 2025, 01:55:00 GMT permalink Post: 11923383 |
Since the preliminary report neglected including when the RAT deployment occurred, I've tried to estimate it based on the picture they did include:
![]() Baro altitude should be around 150ft; using the public cctv video, I estimate this picture was taken between 4-7 seconds after rotation. A wide range, but that was the best estimate I could come up with. Maybe someone else could narrow it down further. 1. ADSB readouts - according to FlightRadar24, the last ADSB transmission was at 71ft AGL. Is that significant given the RAT is seen already deployed at 150ft AGL per the estimate above? At 71ft AGL, the wheels are about 40-50ft off the ground, assuming aircraft attitude is unchanged between there and this image. Is that 1 or 2 seconds after rotation? Does this imply electrical issues? 1a. The timings for ADSB transmissions outlined by MrShed are not in sync with the estimates above - people have talked about a time shift in this thread. I do believe ADSB timestamps are by the receiving station. 2. The preliminary report timings from the EAFR for E2 fuel cutoff switch RUN -> CUTOFF to the RAT supplying hydraulic power disagree with the lower end of the 4-7s estimate above, and are only consistent if this picture was taken 6-7 seconds after rotation, in my opinion, because of the time (4-5s) it would take to cut off the fuel to E2, spool down to where the VFSGs stop providing AC power, and RAT deployment. 3. The Preliminary Report mentions that the RAT deployed "immediately after" lift-off. Again, I have to wonder, why didn't they provide the RAT deployment timestamp, even relative to rotation? If this is in fact the case, does this imply electrical issues, in line with the last ADSB altitude reading? FR24 article https://www.flightradar24.com/blog/f...rom-ahmedabad/ Last edited by appruser; 16th July 2025 at 01:57 . Reason: Added link to FR24 blog post |
Musician
July 16, 2025, 03:52:00 GMT permalink Post: 11923409 |
This was posted sometime ago, but if anyone would still find it useful to pinpoint the location of the aircraft in the 'new' photo from the Preliminary Report (with RAT deployed) I made a crude attempt which placed it roughly midway between the two sets of identical touchdown zone markings, ~245m (803 ft) from the displaced threshold of RW05.
The deemed position of the CCTV camera is only an estimate, based on visual cues. I'm happy to share my workings, should anyone find it useful to cross-reference this with other data they are working on, but I will avoid cluttering up the thread any further until/unless it becomes relevant. You're looking for the point where the LEFT of the two white lines intersects the runway (ignore the white dots): ![]()
Generally don't think it's a good idea to reply to own posts, but in this case wanted to keep things in context. A few interesting items of note:
1. ADSB readouts - according to FlightRadar24, the last ADSB transmission was at 71ft AGL. Is that significant given the RAT is seen already deployed at 150ft AGL per the estimate above? At 71ft AGL, the wheels are about 40-50ft off the ground, assuming aircraft attitude is unchanged between there and this image. Is that 1 or 2 seconds after rotation? Does this imply electrical issues? 1a. The timings for ADSB transmissions outlined by MrShed are not in sync with the estimates above - people have talked about a time shift in this thread. I do believe ADSB timestamps are by the receiving station. 2. The preliminary report timings from the EAFR for E2 fuel cutoff switch RUN -> CUTOFF to the RAT supplying hydraulic power disagree with the lower end of the 4-7s estimate above, and are only consistent if this picture was taken 6-7 seconds after rotation, in my opinion, because of the time (4-5s) it would take to cut off the fuel to E2, spool down to where the VFSGs stop providing AC power, and RAT deployment. 3. The Preliminary Report mentions that the RAT deployed "immediately after" lift-off. Again, I have to wonder, why didn't they provide the RAT deployment timestamp, even relative to rotation? If this is in fact the case, does this imply electrical issues, in line with the last ADSB altitude reading? FR24 article https://www.flightradar24.com/blog/f...rom-ahmedabad/ Note that the good folks at FR24 did not apply temperature correction to the barometric altitude (they corrected for air pressure and runway elevation); pilots on pprune have done the corrections themselves and arrived at slightly different values, so take those altitude numbers with a grain of salt. Note also that the 787 sends altitude in 25 ft. increments, and I don't know how these are rounded (up, down, nearest). We do not know how long the RAT has been deployed in this photo, we only know it can't have been deployed later. I have learned on this thread that the CUTOFF switch will also cause the VFSGs to disconnect, i.e. the B787 systems will electrically isolate the engine from the power buses before it has spooled down. With a dual failure, this would leave the main buses unpowered in short order, so if all of this is correct, the RAT would have clonked into place very soon after the second engine was cut off. This would not depend on the turbine speed. I personally do not know what items are logged on the flight recorder, but I imagine RAT deployment was not among them. If so, the conditions for its deployment would be logged, but it requires an analytical step to conclude it did, and a preliminary report typically has no analysis at all. Hydraulic pressure to the flight controls is likely logged, so the RAT delivering hydraulic power would be a matter of record. Where is the RadAlt antenna on a 787? Is it in the nose, or further back between the main gears? Last edited by Musician; 16th July 2025 at 04:02 . |
jpsingh
July 16, 2025, 07:14:00 GMT permalink Post: 11923479 |
The deployment of RAT has announced Double Engine failure. Also the AutoStart of APU pretty much indicates the same thing . Release of CVR will definitely help.
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sabenaboy
July 16, 2025, 07:16:00 GMT permalink Post: 11923480 |
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Musician
July 16, 2025, 13:57:00 GMT permalink Post: 11923742 |
As I've previously posted, there is the fact that the ADS-B data (in your diagram) continues long after electrical power from the engines would have been lost. Someone recently posted that the engines don't even need to run down for this to happen, saying that operation of the FCS to cutoff would shut down the engine VFSG's.
![]() https://fliphtml5.com/quwam/qhdw/Boo...cs_Electrical/ (page 96) I don't know if the transponder is on the captain's instrument bus, but if so, it would have power from the main battery while the RAT is being deployed. We are definitely seeing the loss of thrust in the ADS-B data. |
Triskelle
July 16, 2025, 18:21:00 GMT permalink Post: 11923904 |
From the discussion about the switches it would seem impossible to me that someone sitting in either the pilot or co-pilot seats could
almost simultaneously
unlatch and move both switches - although it could be done by someone else in the cockpit using two hands? I can believe that both switches could be reset within a few seconds with one hand though. Would a brief electrical fault (at rotation) show on the FDR as equivalent to a switch to 'off' (closing the fuel valve and deploying the RAT)? Apparently the switches were found to be in the 'on' position.
|
Lead Balloon
July 16, 2025, 22:37:00 GMT permalink Post: 11924040 |
The recorded switch position data, the recorded engine performance data, the aircraft performance and trajectory after take off, the RAT deployment and open/ing APU inlet, the cockpit voice recording that has been selectively and carefully paraphrased in the preliminary report and the physical and electrical design and separation of the switches and the wiring for each system prove, to whatever standard of proof anyone wants to nominate, that BOTH fuel cut off switches were physically switched OFF 'shortly' after take off, then BOTH switches were physically switched back ON 'shortly' thereafter.
Give the FSC switch/wiring defect theory away, hamsters. |
Michael Dowding
July 17, 2025, 14:35:00 GMT permalink Post: 11924443 |
Oldrightie
I am not aware of a part of the prelim report, second paragraph being discussed anywhere. Something I find, if I'm correct, not discussed yet for me surely very significant.
"The EGT was observed to be rising for both engines indicating relight. Engine 1\x92s 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" Forgive my now 20 years into retirement as an F/O on the B737 400 and A320/21 but I still retain my lifelong avid interest in all things aviation. So am I correct in thinking this paragraph indicates significantly that eng2, right hand, core compressor had failed, albeit not explosively? It relit and fuel was being "re-introduced repeatedly "but could not arrest core speed deceleration". From day one I believed that no 2 failed after V1 and that the automatic correction for this on the 787 hid all but a possibly apparent small nose right on its climb out. Additionally I surmised that with all the warnings this produced, the low altitude and few seconds to address such a failure, the first recycle was offered up to the no 1 engine switch, in haste. The immediate result then RAT extension, a check on the engine parameters and an action on the no 2 switch, again in haste on realisation that was down on N2, then, sadly too late, No 1 recycled successfully. Unlike No 2. Heaven knows, a similar mistake was made on the Kegworth B737, when all he time in the world was available compared to AI171. To me the long debate here about suicide is very unprofessional and surely this factual part of the report, has masses more credence, regardless of the consequences facing the AI crew. If this bit about No 2 engine report is as I interpret, I would at least hope, if not already, someone else has picked it up, or at least it will get more attention ere long. God bless all the people so badly affected and I pray the cause will be one day revealed and not be buried to protect the money men. Has been known. ![]() |
appruser
July 18, 2025, 00:25:00 GMT permalink Post: 11924773 |
So I've looked again and I think that basically the ADS-B data is 5 seconds out.
So in the diagram (can't modify right now but I will), the blue bar starts at 5 and ends at 13, max altitude marker at 8. That would tie in with loss of power. It would put, interestingly, engine cutoffs right at the earliest opportunity within the window available with sampling etc. (Incidentally an apology to Musician who I incorrectly told earlier that such a movement would be inconsistent with max altitude record, I can see clearly now this isn't the case!). I think for various reasons the ADSB data's absolute values are offset by some amount, for possibly all of the parameters. But there should be consistency in the deltas for the timestamp (by receiving station), the raw baro altitude, the Flightradar24 AGL values, and the airspeed. Flightradar24 themselves note that for altitude " ... the data is not above ground level, but it is consistent to itself." 08:08:46.55 ... 575ft ... 21ft ... 184kt 08:08:48.14 ... 600ft ... 46ft ... 179kt 08:08:48.61 ... 600ft ... 46ft ... 177kt 08:08:49.01 ... 600ft ... 46ft ... 177kt 08:08:49.46 ... 625ft ... 71ft ... 177kt 08:08:49.92 ... 625ft ... 71ft ... 174kt 08:08:50.39 ... 625ft ... 71ft ... 174kt 08:08:50.87 ... 625ft ... 71ft ... 172kt From the Preliminary Report's airport cctv picture, the RAT was seen deployed at, by my estimate here , 150ft baro altitude, between 4-7 seconds after rotation. So the ADSB readings have to be prior to that. What's interesting is that the ADSB data covers: - 4-5 seconds of time (let's approximate 4 seconds from 46.55 to 50.55, ignoring the 0.32s for the moment) - 50ft of altitude gain - Declining airspeed from the 1st reading to the last in this final segment from the runway. Big questions in my mind: 1. If the loss of ADSB corresponds to the E1/E2Fuel Cutoff switches being moved from RUN -> CUTOFF, why is the airspeed declining for the prior 4 seconds? 2. In 4 seconds, why is there only 50ft of altitude gain? that seems odd. 3. To account for only 50ft of alt gain, if we assume the 1st reading is on the runway just before rotation, the intermediate +25ft alt gain is at rotation (Nose up but MLG still on the runway), and the last 4 readings are in the air (nose up an additional 25ft), that means that 1 second or less after lift-off, ADSB was lost - this is before E1/E2 FCO RUN-> CUTOFF. It's just weird . Last edited by appruser; 18th July 2025 at 00:41 . Reason: added a comma for clarity |
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