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Gary Brown
2025-06-17T11:43:00 permalink Post: 11904233 |
There is a possibility that doesn\x92t get much air time on this forum that satisfies all the \x91facts\x92 ( pprune facts mind you), and requires less mental gymnastics to believe than many of the theories put forward. I\x92m not saying it\x92s what happened at all but it seems much more likely than a TCMA fault to me.
This link is to a Japanese report on a Jetstar 787-8 with GE engines that had both engines drop below idle while airborne due to magnesium salts effecting the operation of the FSV spools. The Magnesium salts came from a biocide dose by maintenance two days earlier. For some reason I can\x92t paste the link but if you google JTSB the report number is AI2020-2. I think it\x92s quite easy to imagine that a simple maintenance error ( 1000ppm instead of 100ppm) combined with extremely bad luck on timing lead to this accident. I think I\x92m favouring a theory like this for its simplicity and the fact that fuel is the elephant in the room when you are dealing with a dual engine failure. 4. PROBABLE CAUSES In this serious incident, it is highly probable that, when the Aircraft was descending for landing, there occurred oscillation in rpm of each engine causing both engines to temporarily fall below idle at separate times because Residue primarily composed of magnesium salts accumulated in spools impeded movement of spools that involved in fuel metering of both engines. (emphasis added) and the narrative taken from the pilots is that while they happened in short order, the engine issues were not simultaneous. Not to say they couldn't be simultaneous, but they weren't. Also, the problems arose in the descent, as the engines were throttled back. Again, not to say it couldn't happen in the take-off, under full power. 3 users liked this post. |
Lord Farringdon
2025-06-17T12:21:00 permalink Post: 11904253 |
It seems pretty unlikely that a bird strike that took out both of those
very big
engines simultaneously would not have been fairly obvious in ways that nearby observers (e.g., the crew, ATC, airport personnel?) would have noticed. Possible, of course, but I don't think we've seen any evidence that points in that direction. Also, for what it's worth, the
Times of London
June 15 story "
New clues point to engine failure for cause of Air India plane crash
" cited here in the closed thread includes this:
A poster in the closed thread pointed out, properly I think, that the Times shouldn't be relied upon for presentation or interpretation of technical information. Like most general news organizations, their reporters and editors (mostly) just don't have the background to assess, filter and explain complex processes and technology. Unlike many, though, the Times can generally be relied upon to seek appropriate sources and report accurately what those sources say. I think it's very likely that Indian authorities have ruled out a bird strike, and I also think those authorities are competent to make that decision. The second box has been recovered and the CVR is being analyzed so hopefully they will give an interim update shortly. |
McDoo
2025-06-17T12:50:00 permalink Post: 11904275 |
What if?
Perhaps?
"LNAV" - "VNAV" or "FLCH SPD" To ensure:
altitude was set on the FGP? Suppose they had left it at zero prior to final departure briefing? Not 787 rated but is it possible that they selected FLCH after take off and the aircraft targeted the zero altitude selection? Doesn\x92t explain the RAT deployment but I have a feeling there maybe more than one hole in this Swiss cheese\x85 3 users liked this post. |
OldnGrounded
2025-06-17T13:44:00 permalink Post: 11904315 |
I'm honestly mystified by the obsession with TCMA. The FADECs control almost every aspect of the engines, so there must be numerous ways they could cause a failure or uncommanded shutdown. So, even if we assume that the engines failed due to faults in the FADECs, why assume that TCMA would be involved?
I think those of us who are persistently trying to learn the details of the sensor inputs to and logic of TCMA (I prefer that characterization to "obsessed with") understand quite well the points you make here — at least those of us whose interest survives in this new thread. However, I at least, and I believe others as well, have also come to the tentative conclusions that (a) the accident aircraft had engines providing little to no useful thrust from nearly the first moments after rotation, and (b) the only possible reasons for that which have been considered here so far involve the sudden and approximately simultaneous shutdown of those engines, most likely by interruption of fuel flow (because that's one of the very few things we know that can do that without producing big bangs, flames and smoke, etc.).
Surely it's more logical to simply posit that some unspecified bug in the FADEC software caused the failure. That bug
could
be related to TCMA, but it could just as easily involve any one of the dozens of other subroutines that likely exist.
Various posters seem to assume that all it takes is an incorrect air/ground signal, and the engines would shut down.
But in fact it would also require the FADECs to read the thrust levers as being at or near idle... AND the engines failing to respond to closure of the fuel metering valve.
I've read the entirety of both threads, and I haven't seen anyone even attempt to explain how a malfunction within the airframe could cause both of those things to occur on both engines (or even one engine!).
Last edited by OldnGrounded; 17th Jun 2025 at 13:46 . Reason: Formatting 5 users liked this post. |
JRBarrett
2025-06-17T13:50:00 permalink Post: 11904318 |
Various posters seem to assume that all it takes is an incorrect air/ground signal, and the engines would shut down. But in fact it would also require the FADECs to read the thrust levers as being at or near idle... AND the engines failing to respond to closure of the fuel metering valve. I've read the entirety of both threads, and I haven't seen anyone even attempt to explain how a malfunction within the airframe could cause both of those things to occur on both engines (or even one engine!).
One day upon returning from a flight, the crew pulled both power levers to cutoff. The right engine shutdown immediately as expected, but the left engine kept running. By the time we in maintenance got out to the airplane, the engine finally shutdown by itself. Troubleshooting found the cause of the problem. The cutoff position of the power lever closed a micro switch that sent a ground to the FADEC. That ground went through two discrete wires. One went directly to one input on the FADEC. The other went through a squat switch on the main gear leg to a second input on the FADEC. The engine would only shutdown immediately if both inputs went to ground simultaneously. If only one input went to ground, the FADEC would delay shutdown for 30 seconds. This was to protect against an inadvertent movement of the power lever to the cutoff position in flight causing an immediate shutdown. The squat switch on the left gear leg had failed in the open position, causing the problem. I am wondering if more modern FADEC engines have similar protections against immediate shutdown in the air? I can see why the designers of the Hawker implemented the system the way they did, because the shutdown command was integral to the power lever, and it potentially could be pulled to the cutoff position in flight by an inadvertent release of the locking mechanism that would normally prevent it from going past the idle stop, whereas modern FADEC engines like found on the 787 have a discrete locking switch. But, if a similar protection against immediate shutdown does exist in the 787, would the engines keep running for a period of time (in the air) even if the fuel control switch was accidentally or deliberately moved to \x93off\x94? 4 users liked this post. |
Capn Bloggs
2025-06-17T14:17:00 permalink Post: 11904336 |
Originally Posted by
Squawk7700
Perhaps?
Originally Posted by
Squawk7700
"LNAV" - "VNAV" or "FLCH SPD" To ensure:
VNAV or FLCH was NOT engaged
after liftoff.
Pilot assumed A/T was managing thrust, but it wasn’t.
Pilot assumed A/T was managing thrust, but it wasn’t.
Thrust stayed fixed or decayed (if levers were moved).
​​​​​​​Speed decayed, aircraft climbed too steeply, energy bled off.
​​​​​​​Pilot assumed engine failure due to poor climb response.
Boeing SOPs typically include a callout at 400 ft like:
"LNAV" - "VNAV" or "FLCH SPD" To ensure:
You're clearly implying a complete ballsup by the crew, making multiple serious mistakes or errors of omission. Last edited by T28B; 17th Jun 2025 at 15:40 . Reason: formatting clean up 9 users liked this post. |
Icarus2001
2025-06-17T14:35:00 permalink Post: 11904353 |
We know there was likely simultaneous dual engine failure very near Vr.
2 users liked this post. |
FlightsofFancy
2025-06-17T15:14:00 permalink Post: 11904389 |
incorrect or no data
Firstly, condolences to all those involved\x85.as someone who also 'trains and checks' pilots and also has many years of Safety Investigation within large airlines it is a semi regular occurrence to depart with incorrect or no data.
Tiger took off in Sydney with NO data in the FMGC, Singapore had a tail strike in AKL after inserting the ZFW as the TOW Emirates almost crashed in MEL for similar reasons. Not saying that this happened here Air NZ a few years ago almost put a 787 in the water out of Rarotonga as they had 100' in the FCU, took off, engaged autopilot and the aircraft pitched down and thrust came off, pilots recovered it at 60agl. Emirates has done similar, so these things happen. Could incorrect or no data coupled with other issues (eg hydraulics, electrical or engine failure) lead to a situation that might have been recoverable with the correct data being unrecoverable? |
Xeptu
2025-06-17T15:39:00 permalink Post: 11904404 |
There are several videos of the survivor being interviewed in India, all of them as one might expect, in the language of the country, with English subtitles. As Mr Ramesh is a British national, many years in the UK, I did wonder if there have been any interviews in English, in which I expect he is fluent. That might/should eliminate errors in translation and make his testimony more clear. I can't find any on the net.
|
rkenyon
2025-06-17T17:19:00 permalink Post: 11904487 |
B787 Skipper.... No longer able to sit on my hands!
The joker that published one or other of the fictional accident reports before the dead are even identified needs stringing up by the thumbs.... Well done mods. OK, some of these theories, just bearing in mind the the flight recorder (there is only one FDR + CVR combined) was in the intact section of the undamaged tail and has been with the authorities for almost five days...... - All you guys who are rushing down the TCMA rabbit hole: If it was established that a software error drove both engines to idle without warning, after rotate.... Don't you think the worldwide fleet of B787s would have been grounded by now? Such a glaring failure would be absolutely inescapable on the FDR. Whatever was wrong with this aircraft was present at rotate, unbeknown to the crew. The fact that no ADs or notices to operators have been issued usually means that the cause is known and the aircraft was serviceable. The statement from a prominent Indian Captain about the skill and tenacity of the crew, right up to the last minute is absolutely laudable. However, the cynic in me says that the way is being paved for some bad news and by that I mean news that will do Air India reputational damage. Expect more management of expectation in the coming days. I'm still going with a) Incorrect derate + low Vspeeds or b) Low altitude capture
Speaking as a B787 Captain..... There is so much rubbish and stupid suggestion being written here.
- RAT out? Almost impossible, I have seen no quality footage that definitively witnesses the RAT being out. Those who think they car hear a RAT type noise might be listening to a motorcycle passing or similar. It takes a triple hydraulic failure or a double engine failure to trigger RAT deploment. They happily went through V1 without a hint of rejected take off so as they rotated the aircraft was serviceable. These are big engines, they take a long time to wind down when you shut them down. I have never tried it however engine failure detection takes 30s or for the aircraft to react and they were not even airborne that long. 7 users liked this post. |
neila83
2025-06-17T17:38:00 permalink Post: 11904506 |
B787 Skipper.... No longer able to sit on my hands!
The joker that published one or other of the fictional accident reports before the dead are even identified needs stringing up by the thumbs.... Well done mods. OK, some of these theories, just bearing in mind the the flight recorder (there is only one FDR + CVR combined) was in the intact section of the undamaged tail and has been with the authorities for almost five days...... - All you guys who are rushing down the TCMA rabbit hole: If it was established that a software error drove both engines to idle without warning, after rotate.... Don't you think the worldwide fleet of B787s would have been grounded by now? Such a glaring failure would be absolutely inescapable on the FDR. Whatever was wrong with this aircraft was present at rotate, unbeknown to the crew. The fact that no ADs or notices to operators have been issued usually means that the cause is known and the aircraft was serviceable. The statement from a prominent Indian Captain about the skill and tenacity of the crew, right up to the last minute is absolutely laudable. However, the cynic in me says that the way is being paved for some bad news and by that I mean news that will do Air India reputational damage. Expect more management of expectation in the coming days. I'm still going with a) Incorrect derate + low Vspeeds or b) Low altitude capture Given they took off at a perfectly normal point, at a perfectly normal speed, I don't see how you come to incorrect derate and low v speeds, or how on earth that would lead to a normal takeoff followed by sinking? 8 users liked this post. |
Yo_You_Not_You_you
2025-06-17T20:20:00 permalink Post: 11904623 |
Aryan Asari, the 17-year-old who filmed the crash from his father's rooftop, gave his original interview earlier in the week to BBC Gujarati, i.e in Gujarati language.
I believe they're native speakers professional pilots on Pprune who might have read or could find the original piece. Could they help to clarify Aryan's statements in English? More of this eyewitness' statements in Gujarati also might NOT have been translated into English. Maybe worth checking for added value. Thanks. Grand mother was the one saying it was shaking . She said her location was even closer to the airport . She also said the plane was silent compared to how others make the sound
while above the sound was there , but leaving sound was missing , You know how much Baloon (plane) makes the sound, this was weird .
1 user liked this post. |
Bristolhighflyer
2025-06-17T20:37:00 permalink Post: 11904641 |
1 user liked this post. |
TURIN
2025-06-17T21:47:00 permalink Post: 11904697 |
The 787 has a very sophisticated diagnostic system. Faults are presented through a central maintenance computer system accessible either through the flight deck display units or from a laptop plugged in to the aircraft (there is a WiFi option but honestly it's a bit clunky and I've only ever used it once). All faults are displayed in ATA order as either active, not active or latched faults. I cannot see how any IFE, lighting, air con or other non power plant related faults could cause the situation that has brought this aircraft down. The IFE is entirely seperate and has its own independent diagnostic system. 1 user liked this post. |
EDML
2025-06-17T23:37:00 permalink Post: 11904770 |
I was struck by a comment in this or the earlier thread that I cannot now find. It was to the effect – I’m paraphrasing – that fuel shut off results in an almost immediate cessation of thrust. (Please correct my paraphrasing if I’m off track.) I was also struck by how quiet the aircraft was in the original video, except for the RAT. (Or was it a motorcycle? Sorry couldn’t resist. Just joking…)
Someone earlier asked how the aircraft could have kept climbing if both engines stopped very late in the take-off roll or shortly after take-off. My answer: Momentum. Slamming the throttles back is a lot slower as the FCU (on a traditional engine)/FADEC spins down the engine slowly - I suppose to make sure that the airflow through the engine remains stable. Regarding the momentum: As the first few seconds of the climb were normal compared to previous T/Os of the same flight (speed & altitude, confirmed by comparison of the RAW ADS-B data) I don't believe the engine failure happened before or on lift-off. 6 users liked this post. |
framer
2025-06-18T00:19:00 permalink Post: 11904793 |
Regarding the momentum: As the first seconds of the climb were normal compared to previous T/Os of the same flight (speed & altitude, confirmed by comparison of the RAW ADS-B data) I don't believe the engine failure happened before or on lift-off.
PM: “ V1 ….Rotate” The PF then begins to rotate the aircraft up to a pre determined attitude which is normally between 13 and 15 degrees. They do this at a rate of between 2 and 3 degrees per second so about 5 or 6 seconds later the aircraft is at its climb out attitude. The PM is then looking at their instruments to confirm that the aircraft has a positive rate of climb, this takes a moment, maybe 1 to 3 seconds then; PM “ positive rate” PF: “ gear up”. So minimum 8 seconds but probably longer between the PM calling “rotate” and the gear being selected up. The relevance of all that is to say that if you suspect that the gear up cycle has been interrupted by a dual engine failure, then the engines may well have been producing thrust up to an altitude of 50-100ft or so, which ties in nicely with the max height reached, distance travelled etc. Mods this is clearly not a theory, just info for those who don’t fly airliners to aid understanding. 11 users liked this post. |
Musician
2025-06-18T04:34:00 permalink Post: 11904895 |
![]() FR24 did do that raw ADS-B data comparison. Remember the GPS position and barometric altitude are sent by the aircraft itself. The altitude is sent in 25 ft intervals, so a shallow curve that is smooth in reality looks janky in the data, due to the rounding of the numbers. From https://www.flightradar24.com/blog/f...rom-ahmedabad/ :
We’ve taken data from AI171 departures for the month prior to the accident flight—including two previous operations by VT-ANB—and overlaid their departure paths on the data from AI171 on 12 June. The accident flight is in red, while all other flights are the blue paths. The data shown here is the uncalibrated barometric altitude, so the data is not above ground level, but it is consistent to itself.
![]() Obviously the altitudes are all uncorrected for barometric pressure, which would've varied with the weather on that day; you kind of have to mentally shift the lines vertically downward. Now I looked for, but couldn't find, the post in the old thread where the rotation was triangulated\xb9, but I remember that it was near the turnoff to the high-speed taxiway, so a few seconds ahead of this ADS-B capture. We only have the video to show us what occurred then. That means the ADS-B data doesn't really tell us whether the first few seconds of the climb were normal or not. When we compare the red line to the blue lines, the data tells us the climb rate had already decayed significantly before the accident aircraft passed over the end of the runway, because the red flight path is much more shallow than the blue flight paths. Please correct me if I'm wrong: to my eye, the data alone does not show that the engines must have failed after rotation, because the data does not demonstrate a normal climb rate. But likewise, the engines can't have failed much before rotation:
This aircraft has got airborne well within the requirements of FAR 25 under which it was certified. It has over 1250m ahead of it passing around 35' based on the video from behind, so the FMC data was not incorrect, the thrust up until after TO was not incorrect, and the CG is not out of range, the time to rotate is within expected range, and the attitude at liftoff is not excessive, the plane is not heavier than expected.
----- \xb9 I found one of them, anyway. The reference is the CCTV video:
You can triangulate the camera location using the aircraft holding short for takeoff and the road sign. Then draw a line from there just to the right of the instrumentation building and you'll find the aircraft rotated with about 4000 feet of runway remaining (11000+ runway length).
Last edited by Musician; 18th Jun 2025 at 17:43 . Reason: footnote 1 6 users liked this post. |
steamchicken
2025-06-18T07:26:00 permalink Post: 11904987 |
There has been a lot of discussion of the possibility that the crew shut down the wrong engine or misidentified some other problem as an engine failure, usually followed by an assertion that nobody would touch the engines before x feet. PPRuNe's own survey, at the top of this very subforum, found a really high base rate of wrong engine incidents:
Also, on the point about sitting on your hands to 400/1000 feet AAL, someone who has already deviated from a standard operating procedure is more likely to go on to make another mistake; that is why the procedure existed in the first place. As a memo item, here are the survey results: Q1. Have you ever shut off the wrong engine in the sim? Yes: 5.4% +0.9% No: 94.6% -0.9% Q2. Have you ever ALMOST shut off the wrong engine in the sim? Yes: 26% -1.0% No: 74% +1.0% Q3. Have you ever witnessed a colleague shut off the wrong engine in the sim? Yes: 16% +1.0% No: 84% -1.0% Q4. Have you ever witnessed a colleague ALMOST shut off the wrong engine in the sim? Yes: 45% +2.0% No: 55% -2.0% Link to original post Senior Pilot Last edited by Senior Pilot; 18th Jun 2025 at 07:35 . Reason: Add link 5 users liked this post. |
Bap7788
2025-06-18T11:50:00 permalink Post: 11905173 |
Hi all,
Disclaimer: I read this thread from hour 1, still scratching my head regarding perf though. I know sound analysis points to higher odds being a dual engine failure with RAT deployed, however I still have some questions if anyone is available to enlighten. So, my questions is related to T/O performance. Is it possible on the 787 to calculate perf in the OPT for F15/20 T/O, and to enter F5 T/O speed on the FMC ? By that I mean do normal procedure, but at the point where you are suppose to enter flaps, CG speed ect…. You, out of habit (if F5 is indeed a habit on the 787) enter F5, but F15/20 speeds ? Or would there be a warning that you have manually inputed speeds that are not correct for the selected flaps and conditions inputed in the FMC ? Thanks for the help ! |
syseng68k
2025-06-18T11:58:00 permalink Post: 11905180 |
Lead Balloon:
The requirement for TCMA may have been specified by Boeing, but that doesn' t tell us who designed and built the solution in this case, though it must have been a collaborative effort between the two parties. Anyway, TCMA may be a red herring, since we still have not defined what, if any, other sources would have authority to issue an engine shutdown command 2 users liked this post. |
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