Posts about: "AI171" [Posts: 57 Pages: 3]

There were simultaneous engine failures, but those were due to massive birdstrikes ( US1549 ) or due to epidemic engine failures on Il-62s of various versions (like LOT 007 or LOT 5055 ).

Fuel related total engine failures like Aeroflot 366 or Air Transat 236 at least had the decency to have the engines starve one after another as the fuel in the individual tanks depleted.

But all those are probably highly irrelevant when considering the Air India accident. An engine disintegration or a heavy birdstrike would have been visible on the videos, a sizeable bird would have left some remains. And gradual fuel starvation would have shown some yaw.

As much as I despise the thought, the issue that got AI171 must have come from within the aircraft, although this most decidedly does not infer any wrongdoing by any crewmember.

Shutting down the wrong engine is not extremely rare:

1. GoAir320 at Delhi
2. Transasia AT72 at Taipei
3. Alitalia A332 at Seoul
4. SA Airlink JS41 at Durban

Not saying it happened here!

The Indian Express is carrying a story ( https://indianexpress.com/article/ci...lues-10077117/ ) that includes the following:"Investigators probing the June 12 crash of Air India flight AI-171 from Ahmedabad to London Gatwick are taking a close look at a February 2020 incident in Gatwick, involving an Airbus A321, in which both engines malfunctioned immediately after takeoff. It led to a Mayday call before the aircraft returned to Gatwick 11 minutes later after a turnaround." ...

..."it was \x93clear from visual observation and wreckage\x94 that the flight suffered a power failure." ...

..."The black boxes and the DVR have been recovered but the officer said that the devices were damaged and file extraction would \x93be a complicated process\x94." ...

... "We will check the technical logs to see if any of the engineering teams or pilots of the previous flight left comments on the performance of both engines"
Assuming there is some credence to the article, dual engine failure due to water contamination is the leading theory. It certainly fits much of the speculation in this thread. It may be that the flight data was not captured and much more reliance will be on forensic examination of the CCTV footage and the wreckage. Those waiting for the flight data to be published may be disappointed.

If the original CCTV footage was made available, together with a detailed survey map of the airport, it will be possible to accurately estimate the takeoff speed and altitude during all the critical periods. My guess is thrust was reduced or lost very early and perhaps before the aircraft left the tarmac. Then shortly after becoming airborne, power was lost resulting in the deployment of the RAT. It is doubtful that the pilots shut down the engines or the wrong engine. Likewise flap/slat misconfiguration is unlikely.

You're absolutely right, Musician! Your text in bold print is what happened! And you and I and many other pilots know what the most probale cause for that is. What evidence do we need?
The EAFR will tell the story, but the reason for the crash will always remain a "mystery" because the B787 was not equipped with EPTPR's! ( E nhanced P ilot's T hought P rocess R ecorders)

I think AI171 will go down in history with MSR990 an MH370.

There you go, that’s the tell I expect. Someone sloshing chemicals around and it was finally been noticed in the paperwork somewhere and then they start checking the accident records or vv

https://www.gov.uk/aaib-reports/airc...-february-2020

The Jeju Air recorders survived the crash, and their data was successfully downloaded. They simply stopped recording when the power failed. (And those recorders were also much damaged.)

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.

Thank you for your reply! There's a lot we agree on; unfortunately, I'll be cutting that from my response here.
Right. ADS-B is transmitted via radio, so reception can be patchy, or obstructed by someone else transmitting on the same frequency (e.g. other aircraft), so not every datagram that the aircraft sends gets received. When that happens, the live display of FR24 assumes the aircraft kept doing what it did, and when another datagram eventually comes in, it corrects the position. It also connects the locations of these datagrams, regardless of whether the aircraft actually went there. For example, in the AI171 there's a 4-minute gap between a datagram sent on the taxiway, and the next datagram sent when the aircraft was off the ground towards the departure end of the taxiway. FR24 then connected these points via the shortest route; but we know that the aircraft actually used the intervening 4 minutes to taxi to the approach end of the runway, where it then started its take-off run. So that was false. (Another source of errors is when different FR24 receivers don't have synchronised clocks, so a mixture of data from these can have weird artifacts as a result.)
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.

Have you ever seen a parabolic trajectory from "the short end"?
Yes.

It's uncertain because the 787 rounds all altitudes it sends to the nearest multiple of 25. The altitudes sent were from 575 ft to 625 ft., but that's MSL and not adjusted for the weather: low air pressure makes that number higher than the actual altitude. FR24 adjusted this to 21ft climbing to 71 ft, but it could've been 30 to 60 or maybe 10 to 80, as it's rounded. I think it's fairly close to 50 feet of climb, though.

1) people taking the MSL altitude literally (625 ft)
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.

The survivor likened the sound to a car engine revving up. If you've listened to a good version of the phone video, you'll have noticed the "vroom" sound at the start that some likened to a motorcycle. That sound is the RAT in action, and you can imagine what that would sound like when it rapidly spins up: like a driver stepping on the throttle with their car engine in neutral. The RAT deploying is a consequence of a dual engine shutdown. It says nothing about whether the TMCA was involved.

[Now I just hope your post is still there as I post this. ]

Indeed, thanks to you for your most informative reply! Great to know we're much on the same page.

I'll strive for brevity here. [Fail, sorry!]

Aha! Very misleading by FR24! Maybe they can devise a way to show where data is missing.

Sorry, I got confused about this ^^^, when you wrote this:

but I'm assuming reliable within the 25ft granularity that the 787 creates, which mostly is neither here nor there, but in this case, not so helpful!

Yes, got it, but wasn't what I was meaning to ask, sorry. My bad. I'm about over this TMCA stuff because it sounds like it's Trade Secret so a lot of guesswork, but the question I was intending was:

If the TMCA did activate and shut off the fuel for whatever reason, what causes the TMCA/FADEC Hardware (and Software) to Reset, since it's independently powered off the engine-driven PMG after engine start? There is so much here that is just so unclear. I haven't seen anything about a Reset input anywhere, and since it's supposed to work only when on the ground, that's not really necessary, as the engine will eventually spool down. At some point before that, the PMG output voltage will go to low enough that the FADEC/TMCA should be forced into a Hardware Reset. That's all fine on the ground, but in the air, the engine will windmill, potentially until.... Is the PMG output fed through a switch/relay that cuts the FADEC/TMCA supply at low (i.e. windmill) RPM, so that a Pilot-activated Engine Off/On cycle can reconnect the Aircraft FADEC Supply link, thus Rebooting the FADEC so that it reopens the Fuel Shutoff valve(s)? It all seems so "awkward". And potentially fatal. Is this a scenario that the designers considered? (Who can answer that one? )

Just now, I realise that if this is roughly what happens, then maybe the engines did commence a restart just before impact, due to the plane being deliberately mushed/stalled to the ground as softly as possible, thereby reducing the windmill RPM. And maybe the engines restarting interfered with that planned landing.

Or maybe I've got this all wrong. I'm hoping someone will tell us all.

Thankfully, Yes. Hope this Reply gets through too.

Disclaimer: the numbers I mention are from publicly available sources, namely Wiki (for the ZFW weight calculation) and a Boeing FCOM dated 2010, and my own estimations.

IMO, if those engines failed just after rotation, there is no way that jet would have got anywhere near 200ft, especially if the fuel was "cut off", as opposed to back to Idle.

At 420k lbs (310k lb ZFW+110k lb Fuel), the (takeoff) V2 Flap 5 is 157kts. The (landing) Vref for Flap 5 I estimate to be at least 160kts (the FCOM I have has no figures for Flap 5 landings; F20 Vref is 154; the manoeuvre speed for Flap 5 is 189). Typically, you'd probably be at V2+15 when you get established in the climb after rotation.

No. With a pitch attitude of around 15\xb0, that's quite a bit of weight being supported not only by the wings but by the engine thrust vector. Cut that and you stop going up very quickly. Note Sailvi's comment above.

ANY reduction in pitch attitude would cause the climb to cease immediately. These aircraft are going so slowly, relatively, and the drag is so high that any small change in pitch attitude will cause an increase in descent rate with very little increase in speed (or no lessening of deceleration).

Not IMO. Basically, the only reason this jet is flying is because of the whopping long thrust vector out the back. It's already almost back at minimum speed anyway for flap 5 so there is very speed to trade. In this case, I wouldn't be trading anything, because the speed reduction rate would be too fast.

My estimate is around 200ft (one wingspan) and I hypothesise the engines were producing plenty of thrust until about 7 seconds, before it stops climbing at around 12 seconds after liftoff.

@Brace , I think you're exaggerating the residual thrust effect at lower RPMs. Of course 70% would get you round the pattern but you're at a much lower drag config and you're going much faster, again less drag. And are improved-climb takeoffs in the 787-8 even a thing? I can't see a two-stage rotation.

I've made up a YT combo video:

The Ministry of Civil Aviation has denied reports that the black boxes from the Air India plane crash are being sent overseas. The \x93Black Box Lab\x94 under India\x92s Civil Aviation Ministry is currently analysing the flight data recorder and cockpit voice recorder retrieved from the wreckage of the ill-fated Air India AI-171 flight. ( This must be the Rs 90 million allegedly state-of-the-art facility at Udaan Bhawan [ with the assistance of Hindustan Aeronautics Limited ], New Delhi which was ready on 9th April 2025 - shouldn't it be more appropriate for DGCA / MoCA to get needed expertise, if at all, to their Delhi facility ASAP ? ).

Source: business today June 19th

\x95 The aircraft was a 777 configured for landing (flaps 20 for the G/A attempt)
\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.

Let me try and summarise one possible scenario and then link in some of the better posts provide evidence relating to it:

• In error, PF reduces power to idle and/or reverse at a speed after V1 (either deciding to reject, or for some unexplained reason e.g. the recent BA incident at LGW)
• Decision is changed to continue take-off, thrust levers moved to TOGA
• Let's say the thrust inputs are similar to NM985 and TCMA is triggered; and engines shut down around the time of rotation
• A/C rotates achieving a maximum speed in the region of 184kts

Relevant "ruling out" questions, with links to posts that add new information:

Q: Would the a/c have enough kinetic energy a 184kts to climb to 100-150ft agl and then reach its final position if the engines had failed at, or just, before rotation?
A: Theoretically possible - see calculation here . NB, the a/c actually flew 1.5km from the end of the runway and 2.3km from the likely point of rotation.

Q: Doesn't the forward position of the gear mean that power failed after the pilots had selected gear up?
A: Inconclusive - had hydraulic power had been lost prior to rotation, the gear could also be in this position - explanation here

Q: If the throttle levers were brought to idle during take-off, would the A/C have applied autobrake, reversers and speedbrake?
A: Yes, although there is a built in delay before reverser and speedbrake actually deploy - see here .

Q: Is the ADS-B data consistent with this scenario?
A: Yes, e.g. the Flightradar data shows the aircraft decelerating rapidly (12 knots in 4.2 seconds) from close to rotation. However, it's not clear how accurate this data is. For one, the altitude data is +/- 25 feet, second, while I was under the impression FR would have received airspeed data from the a/c sensors, this post suggests maybe not.

Q: Does TCMA activation require the thrust levers to be at idle or does it function when the thrust levels are above idle, but where the actual thrust is above that commanded?
A: No, the latter is true (i.e. idle is not required) - confirmed here - there are of course many protections against false activation

Q. Did AI171 have the same software version / logic paths as NH-985
A. Unknown. That a/c had Trent 1000s so to some extent the software is different, but we understand the TCMA logic is broadly the same regardless of engine. I have not seen a post clarifying whether the TCMA software has been updated /changed via SB since 2019 to account for this incident.

Be grateful if posters could refrain from speculative responses "e.g. I think this is unlikely because I feel x". I am not opining on how likely this sequence of events is, simply trying to summarise whether or not this theory has been ruled in or out.

I also recommend this post for a summary to read before posting. .

https://www.pib.gov.in/PressReleseDe...x?PRID=2139785

Status Report on recovery and examination of data from Black Boxes – Air India Flight AI-171

Note the front EAFR is the one with RIPS battery backup.

Thx, this indicates at least two issues:

1. The investigation's reliance on the front RIPS battery backuped EAFR indicates a confirmation of a total electrical power loss;
2. Earlier reports (i.e. AVH, now removed) of successful readout of and observations from CVR have proven outright fake.

Regards,
D Bru

From the link above:
The minister called the crash a "rare case". "It has never happened that both engines have shut down together," he said

So they have no clue even with both recorders read out, why both engines shut down at the same time.

Sabotage on the electrical fuels shut down:
Would require detailed knowledge about the wire routing, which is independent for both engine sides, so any "device" would be difficult to get into the electric harness. I would rule that out, unless they find foreign devices wired in on the wreck, because there are way simpler methods to get an airliner down.

Fuel contamination:
There is no smoke, no puff, nothing visible on the exhaust. Both engines went from clean burning to immediate shut down at the same time within less than a second. I think that is close to impossible with any method of fuel contamination you can come up with. There ist always some mixture you would burn and the less perfect burn rate would show as smoke. At take off you have something around 5kg per second fuel burn rate per engine, so you have to come up with non combustible "fuel" in this rate on the exact time on both engines.
Highly improbable.

I find it very disconcerting that with downloaded recorders the investigators seem to have no clue how and why the dual engine shut down happened. How can they be sure that this unrecoverable problem was/is limited to the AI171 flight.

Do politicians usually get access to the data from their investigators in real time or do they have to wait for the reports like the rest of us? This chap is a junior minister, he was asked direct questions and answered appropriately but why would we conclude he has intimate knowledge of the specifics relating to the date download ?

his comments come from this interview but I don\x92t speak Hindi:
https://www.ndtv.com/india-news/sabo...-mohol-8788920

Two points:

1) I had seen the "50 feet below runway" referenced as well, and double-checked on Google Earth, and could not confirm this. The terrain looks reasonably level. I'd be happy to see evidence for this claim, but until I do, I'll think it's false.

2) The maximum L/D is given for optimal speed, which remains constant throughout the glide. In the AI171 case, drag is balanced not just by loss of altitude (as it is in the optimal glide), but also by loss of speed. The speed decline provides energy, and I suspect that makes up the shortfall you assign to thrust.

Note that kinetic energy is proportional to v\xb2, i.e. a speed loss of 50 knots from 180 to 130 vs 50 to 0 provides 15500 vs 2500 units of energy, i.e. 6 times as much. If you hypothetically hurl a unpowered aircraft into the sky with a catapult (and if there was no drag), hurling it at 180 knots makes it go 6 times as high by the time its speed decays to 130 knots than it could ever go if you hurled it at 50 knots. Of course there's drag in reality, and that also varies with v\xb2, so this is a very theoretical consideration intended to calibrate your expectations.

I remember that someone used some kind of tool to confirm that the aircraft could've gone unpowered for as long as we assume it did, but of course I can't find it again now. :-(