Posts about: "ADSB" [Posts: 141 Pages: 8]

I can't speak to the glide ratio but the other numbers are rather off.

For example the distance between the last received ADS-B point (23.066541\xb0N, 72.623189\xb0E) and the impact site (23.055547\xb0N ,72.612406\xb0E) comes out to 1.6467km (~5403 ft) using the Haversine formula. That's significantly less than 2km (~6562 ft).

The aircraft also keeps climbing past the last received ADS-B data point, and visibly attains more than both 100 ft and 200 ft in height above the ground (easily judged by the wingspan of 197 ft), though not by much in the latter case.

In prior posts, I used approximately the same numbers and came to a similar conclusion (we can't rule out the possibility that there was a least idle thrust available after the loss of thrust), using a guess of a 44% reduction for the configuration from a max L/D of 21. Starting with the height and distance being approximate however, we also don't know what the airspeed/angle of attack was at any point in the descent versus the speed for the maximum (and unknown) L/D for the gear and flaps extended and the RAT out, the amount of headwind, the increase in L/D in ground effect (at a height less than the wingspan) over other than a smooth surface, thermal activity in a urban area, the distance gained in the flare at the end, etc.

Best glide performance doesn't start until the pilot pitches the nose down and establishes best glide. As near as I can see, the nose never pitches down.

Yes. I simplified. The point stands that the throttle needs to be pulled back, as it was in the ANA event, because that was a landing and not a take-off.

First, you posted a good summary. I'd have added "unanticipated hardware fault" and "unanticipated software fault" as generic causes.

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.

It has been mentioned before that this capability existed as part of the N2 overspeed protection: the FADEC would shut down a runaway engine by cutting its fuel before it disintegrates.
The thrust lever sensors are wired directly to the FADEC (and hence the TCMA). No data bus is involved with this item.

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 50 feet (?) below aerodrome elevation .
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.

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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.

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.

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.

Which, as confirmed in the earlier thread, is about where GEARUP is typically called. I say those two events are linked, led by GEARUP, but it could be coincidence. Though I don't think so. Coincidence usually refers to unrelated events and that would be very hard to say, here.

On that point, the gear, as far as I can establish (not openly published according to Google), weighs around 8-odd to 10 tonnes. Typically, retracts in about 10 seconds. I estimate it's no more than a 2 metre lift. As far as I can work out (using 3m to make the value higher), that requires about 30kW (rough estimate, budgetary figure, not accounting for it being a curved path, so it's probably higher closer to fully up), but whether wind pressure affects it, I have no idea. Anyway, 30kW isn't a huge (additional) load on a 225kVA alternator. Less than I'd imagined.

Now I'm wondering how big (power ratings) the hydraulic pump and motor are? No doubt, they're driven by a VSD. Can anyone comment, please?

It would definitely be nice to narrow that down; I can't do it, and your method is not convincing me.
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.

I'd agree, without expert knowledge there would have to be big assumptions, but I expect that Aircraft Flight Engineers could do it. Probably already have.

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.

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.

Okay, didn't know that, I guess suggests means it's uncertain? Can you tell me from what height to what height it suggests this?

And why all the wrong figures for the height attained, quoted in previous thread? Can't all be the atmospheric conditions.

Haha! Even a stone (the right shape) can do that, and I'm not disputing that kinetic energy can be converted to altitude. Wings are useful for that... Just curious to get an idea of how much in this case.

To be honest, i believe that taking a lot of the evidence into consideration, it is possible to arrive at a limited number of scenarios for what is most likely to have happened.

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?

To me, since the world seems to be watching this forum, and we are getting no feedback from the authorities, what is posted here might be useful in helping the investigators look at things they might not have considered. Besides, as Icarus2001 has kindof suggested, it's probably a very good thing that there are clearly lots of keen eyes on this.

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. ]

For comparison, the ADS-B data show the ground speed dropping off from 184 knots to 172 knots over 4.3 seconds as the aircraft climbs.

You would expect that decrease given the winds reported that day. The winds at 100 feet AGL are generally higher than at ground level.

I posted my first-cut analysis in the earlier thread.
I've had a bit more time to analyse now.
Those ADS-B data points (and particularly the rate of deceleration) are EXACTLY what you would expect to see from a total engine failure at or very shortly after TAKE-OFF
(it implies a 13:1 L/D which must be pretty close for gear down and flaps 5).
It places takeoff at 700m before the runway end @ ~185kt
Based on those, max altitude was c250ft @ 140kt (or the equivalent total energy equivalent), 500m after the end of the runway.
13:1 L/D would also get you groundspeed on impact of 120kt
Do those numbers make sense?

Exact location of house, Approx distance of 1.5 km from end of runway to crash site .

Coordinates of the camera : 23\xb003'42.3"N 72\xb037'03.5"E

The Approx Camera location of the Balcony is the Red Mark . Can the speed be calculated . Does the speed line up with the ADS B data , Does it Gain Any speed after this Balcony point ?

Co-incidently Another Witness is the Grand Mother of the Balcony Teen, she was closer to the airport as per her . she is saying that the engine was silent after it passed over (but making sound , when it was Over , RAT already deployed?? ) and made offhand comment it was gonna crash . Found that out later .

PPL IR engineer in air trafic flow management, so not quite the right kind of engineer to talk about physics and total energy.

Nonetheless, I ran some calculation with the Eurocontrol BADA total energy model equation using a rough estimation of the height/time profile from the CCTV footage (wingspan yardstick method) and an approximation of the drag using a constant drag hypothesis of 200 kN. That amount of drag is about what a fully configured B788 on final approach generates, I felt it was an acceptable approximation for a less draggy configuration flown at higher than normal AoA but I could be very wrong. I used the total energy equation to calculate speed, inputs are the the height gains and the drag hypothesis.

I find a B788 with a mass of 207 t and an initial speed of 185 kts with no thrust from the rotation onward could theoretically have traded 50 kts for 190 ft before descending back down at speeds between 135 kts and 130 kts, coming back to take off elevation 1950 m after the last ADSB position. The flown distance is sort of the checksum in this, it is not an input but rather the output of the model.

I also did the same exercise with the EK521 incident, assuming a 285 t B77W rotating at 155 kts for a go around on idle thrust. I guestimated 350 kN of drag (normal approach in full configuration is supposedly 380 kN) and got a speed decay to about 130 kts at 80 ft which is how high that particular aircraft got before coming back down. I am not sure this is enough to give confidence in my attempt at doing total energy calculation, but at least it doesn't seem too far off.

Retired engineer here.
I remain convinced that the mentioned non-functioning air conditioning system is significant to the subsequent loss of electrical power. A passenger on the incoming leg complained about the air conditioning.
https://www.cnbctv18.com/india/air-i...l-19620259.htm
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 electrical path to a CAC (cabin air conditioner) starts from the engine driven 235V ac bus which could be L1 or R1.
From there 235V ac is the input to a ATRU (auto transformer rectification unit) which converts to +/- 270V DC and that is the input to a CMSU (common motor starter controller) and the output of one of those feed a CAC on the L or R side. This gear is in the aft electrical bay in the P700 and P800 racks.
These get hot and need to have the heat dissipated by the PECC cooling system.
If one CAC or several doesn't work it is either the CAC unit(s) or some part(s) upstream back to the starting point of the 235V ac bus.

Surely the fault would have been noted upon landing at Ahmedabad and items fixed or switched out of circuit. If not, something is pulling down current in a fault condition and may modify how much power is available for other things.

Moving to take off at Ahmedabad the ADS-B fails shortly after rotate.

This is powered by 115V ac which is derived from the 235V ac bus via an ATU (auto transformer unit) and then via a RPDU (remote power distribution unit). The elapsed time from take off commencement to loss of the ADS-B device is probably the point when the RAT is automatically deployed.

The RAT is rated at 235V ac/10 kVA which calculates as 42A of available ac current. There will be conversion losses in the derivation of 115V ac and 28V DC, so not a lot of current and limits on how it can be used.

The RAT needs 130 knots for full power and if that wind speed drops so will the power. As far as I can see the RAT keeps certain gear working that was working in the first place. Could be wrong there and feel free to put me straight.

None of the above accounts for simultaneous engines flameout but it does contribute to the timeline.

A big question is whether the RAT deployed due to electrical failure which subsequently stopped the engines, or did the RAT deploy due to the engines stopping alone which took out the primary electrical 235V ac buses.
Just a few thoughts, after reading all the posts.

For those postulating the RAT was not deployed, what counter explanations do you have for the following clues?

• Distinctive RAT sound in the rooftop video, audio analysis here .
• RAT visible in rooftop video, example in this image .
• APU door open suggesting auto APU start, suggestive of a full electrics failure (one of the criteria for auto RAT deployment)
• Loss of ADSB data suggestive of a full electrics failure (one of the criteria for auto RAT deployment)
• Unusual gear forward tilt position, suggestive of hydraulic failure and/or full electrics failure (one of the criteria for auto RAT deployment).
• Loss of all thrust, ie dual engine failure (one of the criteria for auto RAT deployment)

Great summary. I've already mentioned the first below, but I'd add another:

• The existence (and timing) of the flyby video by a young lad who apparently lived where the footage was shot from. With planes flying past every few minutes, why would he choose to film this one, before he could even see it? The video starts with the plane still approaching, out of view, and his position suggests it was unplanned, before he could move to a better vantage point. I say he already knew it was extraordinary - from the sound.
• Eye witness account from the mother of the lad who filmed the flyby, apparently said that the plane was "shaking". I'll assume she didn't know how to describe it properly, and that maybe it sounded like it was shaking, from hearing the noise from the RAT. Or it's a translation issue of a word/s with multiple meanings or used colloquially.

One question - are there two exterior doors to the APU compartment, one on top, one below, presumably inlet and outlet of cooling airflow? I've seen photos showing two open doors, but the lower one could be something else, and busted open during the crash.

On this matter, your numbers fall within the range I earlier calculated from doppler shift on the rooftop video's audio, so yes the numbers make sense and, given the circumstances, are reasonably close together.

I also placed the relevant positional data (last ADSB, video source, resting site) into a GIS application and used this along with the audio stream duration to calculate average speed. Obviously it is necessary to correct the speed of sound for environmental conditions but even with this I wasn't happy with the early results I got. At about this time I came to a view that this information wasn't really going to help anyone much so didn't go any further.

From detail that may be retrieved here the FAA noted that Boeing made the following 'Request for correction' (my bolding to highlight why I quote this):

"Boeing explained that the RAT will remain operational as the airplane decelerates through the minimum RAT design speed of 120 knots, not 130 knots. Boeing expressed that the performance of the RAT was shown to meet the Boeing Model 787 requirement that specifies 120 knots as the minimum RAT design speed. We agree that the RAT will remain operational as the airplane decelerates through the minimum RAT design speed of 120 knots, not 130 knots..."

Again I'm not sure this is of any particular utility now, but is included here in the interests of ensuring as much factual data is available as possible.

FP.

FR24 has the GPS lat long position at each time - ground speed is then simply distance travelled over the time interval. The METAR quoted 25007KT and that should increase with height hence the nominal decrease in ground speed over the later ADS-B values - and probably the slight drift off the centre line once airborne.

An earlier poster defined the 787 ADS-B transmits with a height granularity of 25' - which explains the FR24 figures and I might posit that it was just about to transmit a 25' height increase when the electrical failure occurred.

The rooftop video records a nominal 14s flight time with RAT out throughout.
The CCTV video records a nominal 32s (from rotation) and subjectively the aircraft stops climbing 14s after rotation - meaning 18s of descent of which 14s are captured in the rooftop video.

If we accept the RAT is out then it must have been deployed about 12-16s after rotation, presumably immediately after the 4s of ADS-B data.

Another post referenced the RAT only supplying electrical power after 10s - I find that hard to believe, not instant obviously because there has to be some stabilisation time and startup/boot time but it would imply the LH flight instruments would only be active very late. Hopefully the RAT hydraulics would be effective quicker than that.

Resubmitting following some Mod Feedback and a significant re-write. Yes, it is speculative

I have a theory that I'd like to share. It brings together various pieces of known information, along with 30+ years of my experience as an aircraft engineer that forms a plausible (IMO) explanation of what may have happened.

We Know - From the Video's and the ADSB Data:
That up to and for the first few seconds after take-off appears relatively normal.
The AC appears to lose thrust without e.g. birdstrike or other spectacular smoke /fire producing event.
That the RAT deployed.
That the pilot reported 'Thrust not achieved' [Edit - We dont 'know' this - it is heavily reported]

We can see that the AC had a relatively busy schedule in the few days prior to the accident flight, so there was no significant downtime for maintenance activities that could have caused incident.
The AC flew DEL-CDG on 11 Jun with quite a racy turnaround in CDG of 1h12m. The centre tank would have been empty at CDG on arrival, and would have been partially filled for the return CDG-DEL.
CDG-DEL Arrived 01:47 am IST. Again the Centre Tank would have been empty. But quite a bit of fuel in the wings.
8 Hrs later, at 09:48 am IST the AC departed DEL-AMD. For such a short-hop, Fuel upload would have been minimal, merely a 'topping up' if at all. Certainly nothing into the Centre Tank.
DEL That night was fairly hot and humid - 57% at 02:30, 54% at 05:30, 44% at 08:30. That wing tank fuel could have picked up a fair amount of water.

The flight DEL-AMD would have only used the wing pumps. Thus any water in that 'overnight' fuel would have been vigorously stirred and evenly suspended. At concentrations that would cause no ill-effect at all.

The AC was on the ground at AMD for 2 Hrs, from 11:17am to 1:17 pm IST. The AC would have re-fuelled, first filling up the wing tanks to the top, then filling the centre-tank to whatever quantity necessary. There was enough time for water in the wing tanks to settle out.

The B787 Fuel system has pumps in the wing tanks, and pumps in the centre tanks. The Centre Tank pumps are also known as 'override' pumps because they output a higher pressure than the wing tank pumps, thus ensuring that with all pumps running, the centre tank fuel is used first.
Should the centre tank pumps stop, due to either filure or running out of fuel to pump, the wing tank pumps then produce the pressure.
In the event that all pumps stop running (e.g. an electrical failure), the engines will suck the fuel from the wing tanks. The 'sucked' fuel comes from a dedicated pipe in each tank through the 'Suction Feed Check Valve' (so that pumped fuel doesn't just exit through the suction tube). The suction tube pickup is in a slightly different position to the wing pump pickups.

It is conceivable to me that the suction tube pickup could have been immersed in water, settled out from the fuel in the wing tanks.

Then - at start-up of the aircraft in AMD, The engines would have been supplied with fuel from the centre tank. Fresh Fuel. All OK. Wing pumps running and doing not much. But, I speculate, the suction pick-ups immersed in water. Waiting.

Start up and taxi out was all normal. Runway acceleration up to v1 appears normal. V1 - Rotate - (positive rate - Gear up? - Not my debate).
But somewhere around that time, I speculate that a significant electrical failure occurred. Enough for the RAT to deploy. Enough for the fuel pumps to stop. I'll not speculate on the cause. We know that it can occur, that's why the RAT was designed to operate.

The engines at that point were at TOGA thrust. In a significant electrical failure, the engines will keep on doing what they were last told. Keep that thrust stable. So the AC climbed for a few seconds more. The pilots did what they were trained to do for a power failure, manage that, thankfully the engines were still going well...

But there was only so much 'good' fuel in the lines. The engines sucking fuel themselves, the fuel would now be coming from the suction pickups, a different supply. A supply likely heavily water contaminated. It would take a few seconds for that contaminated fuel to actually reach the engines, but when that contaminated fuel hit, Thrust would have been significantly reduced. The EEC's would have been doing their best to maintain the thrust, firewalling the throttles would probably have little effect at that exact moment. The engines would have likely worked through that bad fuel in a shortish period of time, but a period of time that our crew did not have. A fully loaded aircraft producing less than take-off thrust, is not sustaining enough thrust for continued flight. The rest - is down to the skill of the crew in deciding exactly where to hit the ground within the very narrow range of choice they had.