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Musician
2025-06-17T09:56:00 permalink Post: 11904155 |
Bird strike ruled out
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, I expect the airport would've sent a car out to check the runway for evidence. Since we agree that the engine failure occurred near rotation, and that rotation occured well inside the runway ( see e.g. fdr here , or the granular ADS-B data), that car would've encountered a bloody mess, and we'd all know about it by now.
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:
The Indian authorities indicated that a bird strike has been ruled out.
\x95 first, we have seen fake reports circulating; \x95 secondly, News18 rates badly on mediabiasfactcheck.com: "Launched in 2005, CNN-News18 (formerly CNN-IBN) is an English-language Indian news television channel based in India. We also rate them Questionable based on a poor fact-checking record with numerous false claims." That leads me to consider that this "exclusive" might be sloppy reporting based on a fake\x97I have no way to know whether it is legitimate or not. At this point, I feel we can only rely on information being official if it's published through an official website, or if there's independent reporting or a video clip from an official press briefing. I do believe the accident was not caused by an animal strike, for many reasons. But I wouldn't believe it based on unsourced reporting alone. Subjects: AAIB (All) AAIB (IDGA) ADSB Bird Strike DGCA Dual Engine Failure Engine Failure (All) 4 users liked this post. |
Musician
2025-06-17T10:08:00 permalink Post: 11904163 |
Fuel temperature
you mention temperature - got me thinking. Not a pilot (yet) but I am an engineer. A packed 787 sitting out on the tarmac engines running for 3 hours in 41 degree heat with no AC - filled with potentially very warm fuel - what\x92s the chances the fuel could heat up to 49 degrees? Celsius not Fahrenheit. Just wondered what the chances were that it was vapour lock in the fuel lines?
Quoting MR8, 15th Jun 2025 21:54 from the other thread:
With an ambient temperature of 42 to 46 deg C, it is doubtful if any GA aircraft could fly from this airfield, as AvGas suffers from Vapour Lock at 38 deg C.
Jet-A is not so easily affected, but I hope the temperature of the loaded fuel was recorded when uplifted. Subjects: None 3 users liked this post. |
Musician
2025-06-17T10:51:00 permalink Post: 11904195 |
Enhanced Airborne Flight Recorder (EAFR)
Since it has been reported that the "FDR" was found, they also have the "CVR". 6 users liked this post. |
Musician
2025-06-17T19:23:00 permalink Post: 11904582 |
Engine parameters are generally data linked in bursts. Usually every 30 minutes. If an engine parameter goes out of limits normally an alert will be sent immediately but in this case I doubt the alert would have been sent before the power interruption. The black box will tell the story.
Last edited by Musician; 17th Jun 2025 at 20:54 . Subjects: Parameters 3 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 Subjects: ADSB AI171 CCTV EDML Engine Failure (All) Engine Shutdown FlightRadar24 6 users liked this post. |
Musician
2025-06-19T04:40:00 permalink Post: 11905712 |
Air India Radar Altimeters are reported to be 5G-safe
Here's a source to (hopefully) put the 5G speculations to rest:
As 5G telecommunications technology rapidly expands, India's Directorate General of Civil Aviation (DGCA) has issued a directive requiring airlines to upgrade their aircraft's radio altimeters (RAs). This directive avoids potential interference between the new 5G telecommunications technology and the existing aviation equipment. For example, Air India, a fleet comprising 39 % 787s and 777s, stated that retrofitting an RA is an overnight process that would not disrupt flight schedules. These models in Air India's fleet already possess the new RAs. Last edited by Musician; 19th Jun 2025 at 04:54 . Subjects: DGCA 1 user liked this post. |
Musician
2025-06-19T11:21:00 permalink Post: 11905944 |
Subjects: None |
Musician
2025-06-19T13:38:00 permalink Post: 11906027 |
Instead, look at the CCTV video, and consider that the wing span of the aircraft is ~200 ft. I hope you'll agree AI171 didn't come close to 400 ft. AAL at any point. Last edited by Musician; 19th Jun 2025 at 13:53 . 8 users liked this post. |
Musician
2025-06-19T16:03:00 permalink Post: 11906148 |
![]() Draw your own conclusions. Personally, I trust there were no issues. Subjects: None 4 users liked this post. |
Musician
2025-06-19T21:50:00 permalink Post: 11906413 |
TCMA requires that the pilot pulls the thrust levers back to idle, and that the engine fails to spool down to idle as commanded. Only then will it shut off the engine (on the ground). Pilots try to avoid pulling the thrust levers back to idle when they're taking off. For that reason, TCMA has never triggered during take-off before. Subjects: TCMA (All) 5 users liked this post. |
Musician
2025-06-20T05:30:00 permalink Post: 11906603 |
TCMA things, imagination and evidence
You may be surprised to know that TCMA doesn't require that, it just requires a differential between commanded and actual thrust.
It has never triggered during takeoff until now. Maybe it still hasn't been. We'll see. Given there is an actual example of a 787 in the wild shutting down both of it's engines when it shouldn't (ANA), I'm surprised how complacent people are that this couldn't be the cause..Software can always have weird corner failures that could never have been thought of or tested. Note that the thrust lever actuators are wired to the FADECs, and that the TCMA gets the T/L position from that. For TCMA to trigger, it has to determine that its FADEC (on that engine) failed to achieve a commanded reduction in thrust. So we're either looking at a weird, unprecedented edge case, or a FADEC failure, or both.
Just so I have this clear, are you saying that the implementation of the TCMA functionality involved
no
new components being added to the pre-existing FADEC? Are you saying, in effect, that the two switch relays described in the TCMA patent application, which relays and their configuration achieves the described two channel redundancy, were already there as components or are mere depictions of what the software does itself?
Originally Posted by
Lead Balloon
I am not suggesting you are wrong and, as I've said before, the descriptions and schematic in the patent application are just 'big hands / small maps' concepts. However, if TCMA functionality "is simply a bit of software in the FADECs", merely sending a 1 or 0 or other signal into a point in the pre-existing FADEC that already had control over fuel cutoff (with the TCMA software merely monitoring data busses, rather than direct sensor outputs, to work out thrust lever position and whether or not the aircraft is 'on the ground' for TCMA purposes) I for one would really like to know that for sure and get my head around the implications.
With a MCAS crash, it required a hardware problem with an AOA sensor, used as input to a correctly working MCAS, to cause the aircraft to behave erratically. With a correctly working TCMA, I believe it'd require two hardware problems to get TCMA to shut down the engine, as there'd have to be an implausible thrust lever reading, and a FADEC/engine failure to process it within the TCMA allowed range ("contour"?). On both engines, separately and simultaneously. That leaves a software problem; it's not hard to imagine. The issue is, at this point it's just that: imagination. I could detail a possible software failure chain, but without examining the actual code, it's impossible to verify. We simply don't have the evidence. I could just as well imagine a microwave gun frying the electronics on both engines. An escaped hamster under the floor peeing on important contacts. A timed device installed by a psychopathic mechanic. There's no evidence for that, either. This process is a way to psychologically cope with the unexplained accident, but because it lacks evidence, it's not likely to identify the actual cause. We've run the evidence down to "most likely both engines failed or shut off close to rotation, and the cause for that is inside the aircraft". Since the take-off looked normal until that failure, we have no clues as to the cause hidden inside the aircraft. We need to rely on the official investigation to discover and analyse sufficient evidence. The post-crash fire is going to make that difficult. "Both engines failed or shut off close to rotation" explains all of the evidence : it explains an unremarkable take-off roll, loss of lift, absence of pronounced yaw, loss of electrical power, loss of the ADS-B transponder, RAT deployment, the noise of the RAT banging into place and revving up, emergency signs lighting up, a possible mayday call reporting loss of thrust/power/lift, and a physically plausible glide from a little over 200 ft AAL to the crash site It explains what we saw on the videos, what the witness reported, where the aircraft ended up, and the ensuing sudden catastrophe. I don't believe we have evidence for anything else right now—I'd be happily corrected on that. ----- Edit: the evidence of the crash photo with the open APU inlet door, and the main gear bogeys tilted forward, are also explained by the dual engine failure/shut off. Last edited by Musician; 21st Jun 2025 at 06:48 . Reason: more evidence Subjects: ADSB APU Dual Engine Failure Engine Failure (All) Engine Shutdown FADEC Fuel (All) Fuel Cutoff Mayday RAT (All) RAT (Deployment) TCMA (Air-ground Logic) TCMA (All) TCMA (Shutdown) Takeoff Roll 17 users liked this post. |
Musician
2025-06-20T09:15:00 permalink Post: 11906759 |
EAFR documentation
Do both EAFRs run on emergency power? Could it be possible that only ONE (if any) EAFR unit was recording after the supposed loss of thrust on both engines? If the other one is severely damaged we might as well end up with NO EAFR data from the critical last part of the flight. Perhaps both units are severely damaged? I\x92m not convinced your optimism is entirely warranted.
![]() The black rubber cap protects a multi-pin connector. ![]() The white cylinder is an underwater location transmitter. ![]() The forward EAFR has its own backup power. Source: https://www.geaerospace.com/sites/de...rder-3254F.pdf Subjects: EAFR 7 users liked this post. |
Musician
2025-06-20T09:25:00 permalink Post: 11906769 |
Here, at least one EAFR has its own power source, and we're likely to see a record of the engine failures if those caused the power loss on AI171, so that's going to be more helpful. 1 user liked this post. |
Musician
2025-06-20T09:51:00 permalink Post: 11906786 |
Isn't "close to rotation" a little broad? "Close to" can be before or after. If before, and with about 4,000 feet of runway remaining, why did they take off at all? How did they take off, for that matter?
Can anyone do the Momentum / Energy calculations to work out how high the plane would have travelled at the normal climb gradient purely on the momentum it had at rotation? I'll try, see how far I get. A stone, fired into the air at an upward angle, begins to slow down and curve towards the earth the moment it leaves the catapult. It appears to me that the plane climbed at approximately a steady speed until about the 200 ft mark, so I submit that it had adequate climb thrust up to "about" that point. The ADS-B datagrams sent by the aircraft show a much diminished climb rate with decaying speed, betraying insufficient thrust in that phase of the flight. That somewhat contradicts your assertions. I also do not have faith in anyone's ability to watch the cctv video and confidently determine through mere eyeballing that the climb rate did not decay by 15% within the first 100 feet or so. (The ADS-B data suggests the speed diminished 7% for ~50 ft of climb.) Other than your stone, even a glider can convert speed to altitude. So, "close to rotation" is the best I (personally) can do, based on what I know right now; or that I would trust myself to be able to convince others of. Subjects: ADSB 3 users liked this post. |
Musician
2025-06-20T10:56:00 permalink Post: 11906831 |
At that point, the total energy of the system would have comprised of the kinetic energy of the aircraft travelling at Vr, the rotational inertia of the engines and the potential energy of whatever fuel is beyond the cutoff valves.
Q5: Would this total energy have been sufficient to get the aircraft 100ft into the air? Subjects: Total Energy |
Musician
2025-06-20T12:13:00 permalink Post: 11906909 |
Flightradar24 and ADS-B
Thank you for your reply! There's a lot we agree on; unfortunately, I'll be cutting that from my response here.
![]()
Sure, actual data is usually more accurate than eyeballed stuff. But not always. In fact, it's often the eye that determines that something measured or calculated is "Off". How accurate is ADS-B data? I've seen FR24 tracks go way off course then suddenly get corrected / interpolated, frequently. The erroneous data seems to be "removed" by their algorithm, but where are the errors arising? Why this inaccuracy, and therefore, how accurate are the datagrams referred to? I know there were no datagrams received during the backtrack that I accept actually occurred, but that's completely different from receiving erroneous ADS-B data.
However, the datagrams that FR24 actually received were correct. They contain the GPS position of AI171 and its unadjusted barometric altitude, as determined by its onboard instruments. This data is as reliable as the instruments themselves are. (An example here is that the NTSB wasn't sure that the altimeter on the Blackhawk that crashed at Washington-Reagan was accurate; if that is the case, the ADS-B data would also be affected.) On their blog post at https://www.flightradar24.com/blog/f...rom-ahmedabad/ , FR24 have published the data that they actually received.
Sure, the CCTV footage I've seen is very poor, a video, moved about and zoomed, of the CCTV screen. Not easy to judge, but still useful and could be analysed frame-by-frame to compensate for all the extraneous input. Anyway, it's obvious to me that the rate of climb dropped abruptly just before the flight attained its apex, as if thrust was suddenly cut off.
Knowing the momentum to altitude conversion, it might be possible to estimate whether that's true or not. The evident RAT deployment supports engine shutdown, not just engines to Idle, doesn't it? In that case, it would be useful to know at what altitude the engine shutdown took place.
(The ADS-B data suggests the speed diminished 7% for ~50 ft of climb.)
And why all the wrong figures for the height attained, quoted in previous thread? Can't all be the atmospheric conditions.
2) people adjusting for airport elevation (189 ft), but not for pressure: 437 ft 3) people adjusting for pressure, some adjusting for temperature, get 71 to ~100 feet for the last recorded altitude. But while ADS-B reception was lost then (or the transmitter lost power), the aircraft continued climbing; examine the cctv video, knowing the wingspan is ~200 feet, we see that the aircraft reached 200 feet but not much more.
One fact that alters things substantially is whether the survivor's impression is correct that possibly the engines started to spool up again just before impact.
If that's the case then what does that do to the possibility or otherwise that the TMCA system caused a dual engine shutdown?
[Now I just hope your post is still there as I post this. ![]() Last edited by Musician; 20th Jun 2025 at 12:26 . Subjects: ADSB AI171 CCTV Dual Engine Failure Engine Failure (All) Engine Shutdown FlightRadar24 Fuel (All) Fuel Cutoff NTSB RAT (All) RAT (Deployment) 3 users liked this post. |
Musician
2025-06-20T12:31:00 permalink Post: 11906925 |
In this case, not being a 787 jock, my WAG would be a V2 of 165, so they'd be at ~180, and Vref would be at least ~160 (422,000lb, at flap 5). Once those engines cut, it wasn't going much higher at all. Bit of a zoom of possibly 100ft max, IMO. So I doubt the engines stopped at liftoff.
Having done many a takeoff sitting with the nose pointed skyward after liftoff, you just know that if both engines stopped, you would almost immediately stop going up. When you lose only one you have to be quick getting the nose down to keep the speed. If you lost both, you're not going much higher. 1 user liked this post. |
Musician
2025-06-20T15:12:00 permalink Post: 11907045 |
Parabola
By eyeball, did you measure something, did you have something to compare it to? Subjects: CCTV |
Musician
2025-06-20T19:32:00 permalink Post: 11907237 |
\x95 The crew pushed TOGA, but it didn't take, because the aircraft had technically landed already. This delayed pushing the throttle forward. \x95 AI171, starting from 184 knots or more, had substantially more energy to work with. |
Musician
2025-06-20T19:44:00 permalink Post: 11907252 |
electric circuits
To explore the electrical system further see p. 86 of this document. I decided to trace out some electrical paths to equipment and do a few simple calculations.
https://fliphtml5.com/quwam/qhdw/Boo...cs_Electrical/ ![]() The area microphone connects to both EAFRs. The EAFR are normally powered via the left and right main 28v buses. ![]() The RAT powers the backup bus. ![]() The main L and R 28v buses do not receive backup power. ![]() After electric power is lost, the aft EAFR is unpowered, and the front EAFR has 10 minutes power off its internal supply. 4 users liked this post. |