Posts about: "AI171" [Posts: 73 Pages: 4]

I was not aware that we have granular ADS-B data from the a/c itself showing airspeed post rotation (rather than speed interpolated from GPS). Apologies if I have missed it. If it does show acceleration after takeoff I tend to agree with you.

In no particular order, here are some more thoughts on TCMA having caught up on the thread:

If you cut the fuel from two big engines at take-off power, there must be some delay before n2 decays below the threshold for generation (below idle n2), the generators disconnect and RAT deploys. GEnx have relatively long spool up/down times as the fan is so large (and would be exposed to 170+kts of ram air). Perhaps someone has a view on how long this would be, but I imagine it could easily be 10s or more between fuel cut off and RAT deployment. On AI171 the RAT appears to be already deployed at the beginning of the bystander video. That starts c. 13s before impact and around 17s after rotation. This does not prove anything except that the supposed shut down must have happened very close to rotation and could have happened just before rotation while the a/c was on the ground.

As a thought experiment, imagine if ANA985 in 2019 had decided to go around. The a/c rotates and is ~50 ft above the runway, suddenly both engines spooling down, very little runway left to land on and no reverse thrust available. I am struck by how similar this scenario is to AI171. This theory would require there to have been unexpected thrust lever movement in the moments before rotation - but plausibly one pilot moving to reject, followed by an overrule or change of heart - or even a simple human error such as the recent BA incident at LGW - could achieve this. This is perhaps more likely that any sensor fault that you would expect to only impact a single engine given the redundancy of systems.

Tdracer writes that a key requirement of TCMA is to identify an engine runaway in the event of an RTO, in order to allow the a/c to stop on the runway. This will have been tested extensively - it is a big leap to imagine a false activation could be triggered. It did happen on ANA985 but through a very unusual set of inputs including application of reverse (albeit this latter point may not be relevant if TCMA logic does not distinguish between the reverser being deployed or not).

Incidentally there is an assumption the TCMA software version in place on the ANA flight had already been patched and fixed on AI171. That probably is the case but I am not sure it is a known fact.

In summary I remain baffled by this tragic accident. I have not yet read anything that explicitly rules out TCMA activation and it remains a possibility due to the vanishingly small number of factors that could shut down two engines at apparently the exact same moment when they have fully redundant systems. Fuel contamination, for example, has typically impacted each engine a few minutes (at least) apart. I am also cautious (as others have pointed out) of a form of confirmation bias about Boeing software systems with four-letter acronyms.

In my mind the cause could equally well be something completely different to anything suggested on this thread, that will only become clear with more evidence. All of the above also incorporates a number of theories, i.e. that there was an engine shutdown - that are not conclusively known.

Thank you to the mods for an excellent job.

Would moving the levers to idle during t/o not engage RTO? I.e. we would see spoilers deployed and maximum braking applied if that were the case?

Or are you suggesting the levers moved back but not exactly to idle for RTO to kick in?

There has been much discussion here about RAT deployment. Various claims either way have been made, based on individual perspectives of available video and audio.

I am very mindful of just how awful a tragedy this is, and have significant misgivings about disproportionate interest in others misfortune where it carries no purpose, but also recognise that for some people knowing and learning what happened ASAP could be very important, particularly given the present circumstances.

Thus while I sincerely hope that early detail from investigators will give some clarity, in an effort to reduce needless speculation regarding RAT deployment I have taken:

(1) an audio sample from the video of AI171 passing by in which people claim to hear a RAT
(2) an audio sample from a 787 video with RAT deployed on test by Boeing
(3) an audio sample from a JAL 787 video with RAT deployed

And passed these through a FFT in order to gain a more quantitative view of the noise spectra from each event.

A spectrogram of the results is presented below. I hesitate to make any conclusions per se, but observe that there are similarities as well as divergences between them. In all three samples there is a relatively consistent signal roughly centered in the range 113-146Hz that could be what gives the characteristic 'buzz' sound of (apparently) a RAT in operation.

JAL ~141Hz
Test ~146Hz
AI171 ~113-134Hz (prob doppler variation here)


Spectral comparison AI171, B787 with RAT, JAL 787 with RAT



Spectral comparison #2 AI171, B787 with RAT, JAL 787 with RAT


These frequencies seem consistent(ish) with what I got from this video [[url]https://www.youtube.com/watch?v=O1r3CuRwjPc] in which a 787 RAT is being tested - albeit in this case the blades are hydraulically powered and not driven as a turbine. This test showed a fundamental frequency of 135Hz with relevant harmonics above (the second harmonic at 270Hz is higher SPL, no weighting):




It's important to note that the initial recordings are necessarily different; these are not controlled conditions, the recording equipment is probably quite diverse and almost certainly not ideal, and the environmental conditions will also be different. Moreover all of these audio samples have come from video files referenced here, one has no way of determining the provenance or veracity of these sources and, crucially, I have no prior experience of analysing/extracting RAT acoustic fingerprints (nor have I sampled 'control' audio of a 787 passing by /without/ RAT!).

Additionally it's been quite a long time since I did any work with [turbine] noise so given these and other variables I'm not prepared to make any declarations per se, but perhaps more knowledgeable people could. That said, my feeling from what I see is that RAT deployment is not dis proven, and that the apparent fundamental frequency difference between the samples may be explainable by - amongst other things - difference in a/c airspeed, bearing in mind that AI171 was on TO, the others were landing.

Ultimately what I've done here is extremely rudimentary and while it would be possible to go into much more depth I'd hope that more definitive answer would be forthcoming by then, however if anyone wants to discuss specific methodology etc off-line please PM, no wish to add to noise on this thread.

FP.

I was not aware that we have granular ADS-B data from the a/c itself showing airspeed post rotation (rather than speed interpolated from GPS). Apologies if I have missed it. If it does show acceleration after takeoff I tend to agree with you.

In no particular order, here are some more thoughts on TCMA having caught up on the thread:

If you cut the fuel from two big engines at take-off power, there must be some delay before n2 decays below the threshold for generation (below idle n2), the generators disconnect and RAT deploys. GEnx have relatively long spool up/down times as the fan is so large (and would be exposed to 170+kts of ram air). Perhaps someone has a view on how long this would be, but I imagine it could easily be 10s or more between fuel cut off and RAT deployment. On AI171 the RAT appears to be already deployed at the beginning of the bystander video. That starts c. 13s before impact and around 17s after rotation. This does not prove anything except that the supposed shut down must have happened very close to rotation and could have happened just before rotation while the a/c was on the ground.

As a thought experiment, imagine if ANA985 in 2019 had decided to go around. The a/c rotates and is ~50 ft above the runway, suddenly both engines spooling down, very little runway left to land on and no reverse thrust available. I am struck by how similar this scenario is to AI171. This theory would require there to have been unexpected thrust lever movement in the moments before rotation - but plausibly one pilot moving to reject, followed by an overrule or change of heart - or even a simple human error such as the recent BA incident at LGW - could achieve this. This is perhaps more likely that any sensor fault that you would expect to only impact a single engine given the redundancy of systems.

Tdracer writes that a key requirement of TCMA is to identify an engine runaway in the event of an RTO, in order to allow the a/c to stop on the runway. This will have been tested extensively - it is a big leap to imagine a false activation could be triggered. It did happen on ANA985 but through a very unusual set of inputs including application of reverse (albeit this latter point may not be relevant if TCMA logic does not distinguish between the reverser being deployed or not).

Incidentally there is an assumption the TCMA software version in place on the ANA flight had already been patched and fixed on AI171. That probably is the case but I am not sure it is a known fact.

In summary I remain baffled by this tragic accident. I have not yet read anything that explicitly rules out TCMA activation and it remains a possibility due to the vanishingly small number of factors that could shut down two engines at apparently the exact same moment when they have fully redundant systems. Fuel contamination, for example, has typically impacted each engine a few minutes (at least) apart. I am also cautious (as others have pointed out) of a form of confirmation bias about Boeing software systems with four-letter acronyms.

In my mind the cause could equally well be something completely different to anything suggested on this thread, that will only become clear with more evidence. All of the above also incorporates a number of theories, i.e. that there was an engine shutdown - that are not conclusively known.

Thank you to the mods for an excellent job.

Looking at the detailed ADS-B data released by FR24 and the June 10 AI171 data, I noticed that the two flights show the following data at similar points in the takeoff phase
Height :575ft
Speed :182kts
Even though it is impossible that the takeoff weight and outside air conditions are the same on the two flights, we guess that there was nothing wrong at this moment.

I wonder if those reported eight Air Indian 787-8's pulled in for 'looking at', have had any issues with failed power systems, as in the reported and video of this aircraft, having no IFE systems working.,

Wasn't there a post by someone who claimed to have been a (ex) crew member of the aircraft who said that there have been a number a complaints about power issues in that aircraft and it was brough to management's attention, but nothing was apparently taken seriously...?

If it is an AI maintenance issue and considering that the Black Box has been looked at for days now.
AFAIK , there's two black boxes, each with identical data, so only one is needed (theoretically), Plus, AFAIK , the data can be retrieved remotely on these newer boxes.

And as mentioned, if it was a 'software' bug relating to engine cutoff's or other inherent engine issues, then the whole fleet would be grounded - HOWEVER - as in the 737 MCAS debacle, it was known for a long time before the crashes that 'something was wrong' with the pitch control - as was being reported on NASA's own NSRS database even IIRC years before.

And again (I made a post somewhere months ago), why on earth doesn't any airport that is say classed as international, have 4k cameras installed.
Look at how many pages have been "were the flaps out on takeoff", and such like, "Ran out of runway" - even (maybe), Engine thrust could be seen, bogey conditions, tire conditions,
Could answer a lot of information as to "Was the aircraft in good configuration on Takeoff/Landing',
The world has watched hours upon hours of potato cam footage of AI-171 taking off - plus a handheld phone footage taken by a kid, and that's the best a trillion $$ airline industry can do..?

If they had, we would still be looking at potato cam footage as we would only get to see it together with the (cleaned up) FDR readouts and paraphrased CVR protocol in a report +12 months from last week.

Why? Because it\x92s a low value added installation. Cameras might satisfy the public and spotters desire for instantaneous news, but it wouldn\x92t appreciably add to safety. VAAH has been in operation for 88 years, its last fatal hull loss was almost 40 years ago, landing in fog where a camera would record nothing. There are better safety improvements to spend the money on.

I spent some time this morning doing a further quantitative analysis of the flight path of AI171, however I've come to the view that is of little real use to anyone, so I won't be presenting it at this time.

What I do want to say though, particularly after what I saw much earlier this morning, and what I recently read about the young man who took the video many have seen, is a heartfelt acknowledgment to anyone reading this thread who is a survivor, witness, relative, responder, or simply anyone directly affected by this tragedy.

As someone who, unfortunately, has been in a not-dissimilar situation I want to tell you that it's *not* your fault , that it's normal to feel angry, or guilty, or sad, or even not to be able to feel anything at all. It's ok to want to cry at the oddest of moments, to want to kick the hell out of something, to be unable to sleep - or to just to curl up and go to sleep for a long time. This could hit you weeks from now, or it may never happen at all, it will worry you when it does - or not - but y'know, strangely, that's ok too. We can rarely control such strong emotion, it's simply the way we frail humans work, and we don't all feel, or express things, in the same way.

People will tell you that time heals all. You may not believe that right now, and most of us will never be able to unfeel, unsee, unhear, or unsmell, but the passage of time will ease these things. It may take years, or not, but it's ok, there is a future.

If you know someone that's involved, give them a hug, or don't give them a hug if that's what they need too. Space, peace, quiet, or conversely keeping really busy at work with people around are all mechanisms different people may use to cope. Keeping a watching eye and 'being right there' if/when you're needed is perhaps the best thing you can do, along with understanding if that person wants distance.

And, it might seem unbelievably crass that we're discussing what happened to you, to your friends or relatives, but for some of us it's our way of helping - or coping - when we feel your tragedy so strongly. It's a practical way we can help ourselves and others understand, or learn, or even prevent someone else suffering the same way. There will be people on this forum who get this more keenly than others, but no-one intends to hurt.

For those that are interacting here, it behooves us all to be aware of the humanity, to remember before we say anything that real people are hurting right now, and that on this public forum whatever we say could be read by anyone at any time, forever.

Sincerely, FP.

In the US at least, unions would heavily object to 4k cams everywhere at an airport. Inevitable, the footage would be used by corporate to critique pilots. Some how, some way, the bean counters would find a way to monitor the footage to try and save a penny. There have been many calls to place cameras in the cockpits.....100% unions would fight this and be willing to strike over this.

Could you please elaborate on that?

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/ :
The red line is the accident flight, and it covers approximately 4.3 seconds.
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:
For completeness' sake: you can look at the CCTV video, consider the 787's wingspan a flying 200 ft yardstick, and hopefully agree that the aircraft did not get much higher than 200 ft AAL, if that.

-----
\xb9 I found one of them, anyway. The reference is the CCTV video:

Once again tdracer confirmed the PMGs for the FADECs in the first AI171 thread. He even explained the logic behind it and the connections with the onboard electronics:
- Each engine has a PMG for the FADECs
- Only for engine start the FADECs are powered by the aircraft
- Once the engines are running, this connection is opened
- It is verified, that the FADECs are then no longer connected to the aircraft electrical system. A failure to open the connection triggers a "No dispatch" message
- In case the PMG fails, the FADECs are once again powered by the aircraft electrical system

Yes. That is what I have read here, that is my assumption, that is how Airbus does it, that is what makes sense .

But I am being told elsewhere by someone with an A&P badge that that is not quite the whole story, and that the FADEC PMGs do double-duty as the flight control PMGs.

I am hoping for some documentation to confirm/refute that.

Tata group chairman (majority owner of Air India) N. Chandrasekaran had a TV interview with Times Now, an English-language news group in India. I haven't seen the full video (blocked from the USA but someone will surely upload to YouTube soon), but there are some summaries and quotes from the interview appearing on various US sites.

Below are some interesting quotes from an MSN article ( https://www.msn.com/en-in/money/tops...ys/ar-AA1GYiEZ ), including a claim that both pilots but especially the FO had more experience than previously reported:


“There are speculations about human error, speculations about airlines, speculations about engines, maintenance, all kinds,” he said. “But the fact that I know so far is this particular aircraft, this specific tail, AI-171 has a clean history. As for the engines, the right engine was a new engine put in March 2025. The left engine was last serviced in 2023 and due for its next maintenance check in December 2025. Both engine histories are clean,” he told Times Now. “There were no red flags or maintenance issues,” Chandrasekaran said. “Never been safety concerns raised, Dreamliners have been operating for a long time.”

“Captain Sabharwal had more than 11,500 hours of flying experience, the first officer Clive (Kundar) had more than 3,400 hours,” Chandrasekaran stated. “What I hear from colleagues is that they were excellent pilots and great professionals. So, we can't jump to any conclusions. I am told by all the experts that the black box and recorders will definitely tell the story. So, we just have to wait for that,”

Interesting what is not said. While Chandrasekaran enumerates some of the theories about the cause of the crash ("human error, speculations about airlines, speculations about engines, maintenance, all kinds,\x94) the only speculation he goes on to refute is maintenance of the engines - leaving the other possibilities still out there..

@ferry pilot and others who mentioned the seat back collapsing: That was from an entirely unrelated incident on Air India Express flight 611 in 2018 which got poorly rehashed / fakenewsed into a bogus theory over the last week. It was a 737. It did *not* happen on AI171.

For what it's worth, the AIX 611 story in 2018 involved a 737 captain's seat back being overtightened and suddenly collapsing backwards during the takeoff roll. He had been guarding the thrust levers and reflexively grabbed them when falling back, causing a thrust reduction from 98% N1 to 75% N1 or thereabouts. Control was immediately transferred to the other pilot but the inadvertent thrust change was not corrected immediately, and the plane took off a few seconds later with a tail strike, scraping the runway, flying through the localizer and demolishing part of the airport perimeter wall with its landing gear. During the climb, the flight crew ran several system checks and landing gear tests to reassure themselves the plane was fine, then proceeded with the flight, pressurizing the aircraft and whatnot. They evidently did not consult the tail strike procedure. Many hours later they were ordered by company to divert and land quickly after the damage was seen at the airport. After landing, the plane was found to have a fair bit of damage, including part of the perimeter wall's barbed wire fencing material wrapped around the landing gear. But zero injuries, and the plane was fixed and flew again.

It's an entertaining story because of the cause and the happy ending, but had nothing to do with AI171, for which we all await the preliminary report.

There seem to be issues with the evaluation due to damages. Cannot assess the reliability of the source.

https://weeklyvoice.com/damaged-blac...medium=twitter

The EK 777 (EK231) low level altitude capture incident did not include ignoring the FD command with a sensible pitch-up. They exceeded 200kts while still on the runway and exceeded 250kts before climbing above a couple of hundred feet (the reports say 262kts at 175' but I don't know if that's adjusted for QNH). Apparently they had 00000' set and there was no FD pitch up command. No thrust issue in this case.

EK231 had thrust but no pitch. AI171 had pitch but no thrust.

There's less information about the Air NZ low level altitude capture, I don't know how it compares.

To be clear, I don't presume that AI171 had a low level ALT capture. It appears to have had a loss of thrust for an undetermined reason.

No, it's not. You got that value from ADS-B, which is barometric altitude at standard pressure, and when you correct for that, the highest value is ~100 ft. AAL.

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.

Reported 625' pressure altitude, elevation 189', QNH 1001.

So they only got to around 100' height, half the wing span of a Boeing 787? I think it looks higher than that.

189' elevation, QNH1001, the pressure altitude should be around 550'. First readout from ADS-B is 575', highest is 625'. I did not look up if runway departure end is much different there than aerodrome elevation.

Interesting that the readout of pressure altitude doesn't get lower again, after 625', which could support the total loss of all AC (and most DC power?). Transponder possibly stopped working, but one of the pilots was able to transmit a mayday call. So they must have had some kind of electricity available.

So what I mentioned about THR REF / VNAV SPD is probably not applicable. Yes, I did not account for the QNH initially, which makes closer to 100' than 400' AGL.

I will revert to await the official findings then, with a substantial loss of electricity seeming more and more plausible.