Posts about: "FlightRadar24" [Posts: 75 Pages: 4]

Graphic produced from GE and later FR24 data showing the 8 airborne plot points between rotation and the transponder dropping out:



Elapsed time between first and last points was 4.32 s, giving an average groundspeed of 179 kts.

If those numbers are correct about 120kts then. Interesting

FR24 data appears to stop shortly after airborne but well before impact.
That would seem to align with the significant loss of electrics as a result of loss of engine generators theory?
Flaps prematurely retracted shouldn\x92t be a cause of loss of electrical power to the transponder. If electrical power was normal then one would have expected data info until impact, regardless of flap position.

Not a 787 pilot, but given the fairly high weight, calm winds and the 37C temperature, 184kn is not excessivly high for rotation. The data points are ground speed and a small decrease during initial climb doesn't seem surprising. It isn't "decreasing rapidly", it just drops a few knots. Simple geometry plus some small variance in airspeed and wind would account for that much variance and FR24 calculated speeds are not perfect in any case. I think it is more interesting that the data stops shortly thereafter. If the speed continued to decrease that would be an important clue, but we don't have that information right now. The surveillance video seems to me to show the plane at least exceeding a full wingspan in height, that means over 200 feet.

Yes, this is the odd part - from the videos it didn't look like there was any attempt to put the nose down for best glide, and even the pitch up (if presumably from fear) was not very pronounced. It basically came down in the same attitude as during the takeoff. That has me wondering if they even had any controls at all. Very low probability, true, but then both engines out is also a low probability event. 'RAT Push and hold 1 second' seems to be a dual-engine fail memory item on a 787, so both engines out would explain the loss of thrust and the RAT deployment.

The lack of obvious debris/smoke during takeoff might indicate it was something other than a birdstrike, and combined with the loss of adsb (per FR24) right over the runway threshold at 70ft agl, maybe it is indicative of something else causing the simultaneous loss of thrust.

In summary,

Flaps were extended, possibly flaps 5 or 15. Looks like it in the video and clearly shown post crash.

Aircraft reached a height of just over 100\x92 AGL (possibly 200\x92 if you compare wingspan to height in videos)

RAT was deployed. Seen on videos and heard conclusively.

Aircraft rotated at \x91usual\x92 spot. Comparing FR24 data from previous flights over the past week.

Aircraft took off at \x91usual\x92 speed. Comparing other flights.

FR24 data stopped being sent shortly after take off. Possibly indicating electrical fault.

Green and white flashing light reported by survivor. Possibly indicating electrical fault.

Gear bogies were at unusual angle indicating Gear selected up and then interrupted.

No smoke or flames to indicate bird strike. (Edit - still debate about this in the video above where the aircraft is behind a building)

No rudder input to indicate single engine failure.


All speculation but hopefully a pretty balanced summary from the thread so far. It would be great if there was more focus now on what might have caused above rather than talking flaps, birds, 625\x92, etc.

Thank you, and to HI288 too! this combined with the FR24 blog post about adsb loss just over the runway threshold, and the latest DGCA ask for Air India 787 maintenance adds more weight to the theory, IMO, that there was a major technical issue in play here.

I agree it is helpful to seek a consensus on some of these matters.

The most productive responses would be along the lines of:-
(1) I too have read all previous posts and agree that your summary reflects the current consensus,
(2) I too have read all previous posts and agree your summary reflects the consensus HOWEVER I challenge that consensus because... [ [i]EITHER (a) reference to previous post that merits greater credence, OR (b) new evidence supplied],
(3) I too have read all previous posts but I do NOT agree your summary reflects the consensus [explanation required].

It is not necessary for everyone who thinks (1) to say it (although some initial feedback would be useful!). However, if any of the more experienced and informed PPRuNers are thinking either (2) or (3) then it would be instructive to hear that.

FWIW, yours strikes me as a reasonable summary of the best consensus I have been able to discern (as of ~30 minutes ago). There are multiple caveats to each line item, but I presume you've deliberately left those out for the sake of readability, so I'll do the same!

The only comments I would add are:-

- It's a stretch to say the RAT is seen or heard "conclusively". Doubts have been expressed about the video quality and there are dissenting views regarding the audio. If a few more people were able to wade in on the audio point in particular, this could be very beneficial in moving the discussion forward because the presence or otherwise of the RAT is significant to several competing theories.

- On the subject of audio, I am surprised there has not been more discussion regarding engine noise. In the primary eye witness video the (alleged) RAT can be heard distinctly, as can the sounds of distant impact. If the engines were working as expected when overflying the camera and then flying directly away from it, do we really not think the engine noise would be more conclusive, i.e. louder (notwithstanding quiet engines and derated takeoffs)?

Whichever way readers are leaning in the flaps versus power loss debate, surely these two points are pivotal, and we have actual evidence available to discuss?

- Gear bogies: I'm not sure a consensus has yet been reached regarding the angle of the bogies. (I am not personally qualified to comment on this - I am purely saying I don't see a clear consensus just yet among those who are)

- Mayday call: I don't recall seeing a confirmed source for the widely reported mayday. Others have brought this up in the thread but nobody appears to be able to confirm one way or the other. If accurate, its contents are informative. Am I right to presume that you have left it out of your summary due to a lack of confirmation?

Combining all the bits and pieces of info from this thread so far, IMO we can theoretically sequence it thus using the video from the left:

00:18 Rotation. Normal takeoff config.
00:24 Gear up starts. per Raffael with FF.
......... FR24 ADSB last transmission (71ft, 172kt) just before runway threshold. Matches with video aircraft altitude at 1/2 wingspan.
......... ? Full power flameout leaves N2 ~ 60%; Airspeed < 200k so N2 will decay to 15% in 8-10s?
......... ? Takeoff EGT of 900C needs 25-35s to fall below 250C ?
00:27 Gear up stops. per Raffael with FF. Bogies tilted.
......... ? APU starts. 20-55s to 95%N?
......... Per 787 dual-engine fail/stall memory items, PM initiates Fuel Cutoff and Run.
00:28 Visible loss of thrust. Alt ~ 200ft using aircraft wingspan as measure.
......... Matches with eyewitness "within 5-10s ... it was stuck in the air".
......... Per 787 dual-engine fail/stall memory items, PM initiates RAT Switch for 1s. Whether auto or manual, the RAT initiates.
......... RAT "bang" heard by survivor
......... RAT coming online accounts for eyewitness "lights started flickering green and white".
......... Per 787 QRH below 1000ft, PF makes no change to Main Landing Gear and flaps, aircraft pointed straight for best glide.
00:31 Descending visibly, somewhere beyond the runway threshold. Alt ~ 200ft using aircraft wingspan as measure.
......... ? Because EGT > 250C FADEC blocks fuel (T-HOT hot restart inhibit?) so no relight though N2 > 15% ?
......... 787 glide ratio between 16:1 to 25:1 with MLG down, Flaps 5. About 15-20s and 3-5000ft of glide from 200ft?
......... Some flap accounts for the ground pictures.
00:34 ? N2 has presumably decayed to 15%, FADEC flips to X-START: airspeed outside envelope? No hope of relight now.
......... PM/PF transmits Mayday?
......... Video showing RAT deployed.
00:46 APU reaches some fraction of 95%N (APU sound accounting for survivor's perception of thrust?).
00:48 Impact. 4200ft from descent start, 3990ft from airport boundary road. 17s from visible descent start.

if this is a valid sequence, the only remaining question is why the dual-engine failure at ~200ft agl?

with condolences to the families and people affected.

There should not be a max pre-start EGT limit in-flight - that should only occur on the ground for a pilot-initiated Autostart where the starting EGT redlines are lower than for in-flight.

In-flight, the Autorelight function should attempt to restart the engine as soon as a flameout is detected, and for an engine flaming out at high power it might catch it before it even goes sub-idle. Generally, Autorelight will continue attempting until some cutoff N2 at which time it will stop attempting, or if the pilot move the fuel switch to Cutoff. And while the EEC is still powered (via its own PMA) down to roughly 10% N2, the ignition exciters required for Autorelight do get their power from the airplane.

I did read and search this thread, but I found nothing about ADS-B loss just before the end of the runway and at 71 ft high, according to FR24. ADS-B coverage is poor on the ground on the north-east part of the airfield (hence the fake news about taking off from the intersection) but I don't think it would be lost once airborne, except if it has been shut off... electrical failure ?

more precisely, loss of the two Main AC buses (ADS-B not powered by Standby AC)

There could be other reasons not connected with the aircraft systems,

But certainly loss of engines or electrics that caused deployment of the RAT (if that was the case) would be accompanied by a bunch of load-shedding, which would in all likelihood include the transponder.

Edit: Your own reply beat me to it ...

(Can't post links yet, not even permalinks, but see post #740 at present count)

I guess you have to make a post on just this one item to get it noticed!
But I agree that this piece of data deserves close attention, and is potentially confirmatory of certain scenarios which lead to electrical power loss.
I'm no expert on Flight Aware's ADS-B data, but other posts here show other flights taking off on this runway happily reporting data further down the runway and (well) after takeoff.

How else do you explain the cessation of ADS-B data from this flight from shortly after takeoff until the crash?

A slight decrease in two engines is still far better than a loss of one engine, and that has to be manageable.

787 has four main AC buses. Cannot find information on the standby/emergency buses but I would probably expect two.

There's a list of equipment operable on battery/RAT here, but I'm not sure which (if any) is the transponder (26:10):
I think the post you replied to was in the context of mandating APU on for takeoff. Could just say "on if available", though.

I can't see how gear pins would stop you doing anything more than raising the gear. They don't cause engine failure, RAT extension, or uncommanded flap retraction.

If you had gear pins and an engine loss, I could maybe see climb rate being zero or slightly negative. Not the brick impression we see here.

I did raise this earlier... FCOMs say that the bogies remain in the stowed tilt after a gravity drop, but I don't know if that's because the gear has springs to hold it that way without hydraulics, or just they close the valves on the hydraulics so it stays in the last commanded position without pressure.

Extremely likely the RAT was out:

1. there are multiple frames of the video showing ' something' at the position where the RAT is located under the fuselage
2. the sound in the video which is very similar to a deployed RAT
3. the sound analysis posted here by multiple people
last but not least
4. the aircraft stopped transmitting ADSB data shortly after the rotating. This indicates an electrical failure. Other aircraft ADSB data was picked up by FR24 receivers indication there is a good reception of the signal in that area.

People really need to stop using FR24 data if they don't understand it.
This FR24 recording of AI171
https://www.flightradar24.com/data/f.../ai171#3ac3097
only consists of 4 unique ADS-B data messages. The first two were on the apron/taxiway. Then one at the runway intersection. And the fourth and last one just after the aircraft became airborne. That's all.

The two last ADS-B data messages are more than 4 minutes apart. It was 8:04 UTC when they entered the runway at the intersection. The next and last data point was received at 8:08 UTC.

The map view connects these dots, so it looks like a proper track. But in reality the ADS-B receiver barely received anything. It's therefore silly to argue the aircraft stopped transmitting ADS-B data based on this poor recording. The only thing you can say with certainty is that FR24's ADS-B receiver at Ahmedabad has really, really poor coverage...

FR24 has stated that they processed additional frames and have published this separately. There are links to this earlier in the thread. What you see is the first data point is immediately after liftoff and then they are regular for a bit and then they stop. Apparently at least half of the runway has poor coverage and that is what led to the early conjectures that they had done an intersection takeoff. If you look at tracks from other flights from this airport, you'll see the spotty coverage on the first half of 23, but departing flights seem to have good data. YMMV, but that's what I saw when I looked at a few other flights.

There are more data messages than that, which FR24 shared on the day of the accident and which have been posted a few times in this thread. I'm pretty sure there's also been a comparison of this + previous flights posted in this thread that shows that while the coverage at the airport itself is spotty, it's reasonable to expect further messages to have been received before impact.

Not sure how permanent the content at this URL is, but here's a link to FR24's update which has a CSV with all frames received https://www.flightradar24.com/blog/f...rom-ahmedabad/

Somebody on this forum did some analysis with FR24 data of this flight and other AI171 B787 flights.
See this article for an overview of all scenarios. It all looks very like to an commanded dual engine shutdown. Why nobody knows.

The comments that you are criticising are based on a subsequent release of ADS-B data from FR24 containing 113 unique messages.

While those still have the 4\xbd minute gap while the aircraft was presumably backtracking, they resume during the latter part of the takeoff roll where reception is clearly better.

There is little doubt that when they abruptly cease after the aircraft is airborne it's because the plane has stopped transmitting.