Posts about: "RAT (Deployment)" [Posts: 361 Pages: 19]

This incident is very perplexing to me. This is my first post on here and I am not a pilot. I have over a decade of experience in the RAAF as an engine fitter on Mirage and Hornet aircraft. Albeit a bit of time ago.
I have watched the video's and looked at the FR-24 data a hundred times. To me it looks like a normal rotation and at WoW everything starts to go wrong.
Airspeed starts dropping off immediately going by the FR-24 data. If reports are correct the pilot makes his Mayday call. FR-24 data stops.
In the video from the balcony I agree the RAT is out and operating but I can also hear the engines at idle or just above (maybe flight idle).
If the captain manually deployed the RAT this makes sense to me. In both video's I don't see any aircraft behavior that would suggest they are not flying the aircraft.
Is there an electrical fault at WoW that renders the cockpit dark and therefore manually deploying the RAT (possibly initiating APU start, inlet door is open at crash site) would make sense to restore cockpit power.
I can't understand any pilot shutting down both engines at 200ft AGL. He would surely know that his fight is over at that point.
I am not ruling out pilot error (configuration or otherwise) but my hat goes off to two pilots that I believe were trying to fly this aircraft until it hit the ground.
Sorry if my wording is a bit off but mine is military background not commercial.

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.

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.

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

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?


In this crash, why would you do it? I cannot see the relevance of manually deploying the RAT. Given the altitude of the plane, the loss of lift/thrust, and the on coming site of residential buildings fast approaching why would you manually deploy the rat. At high altitude, tens of thousand of feet, yes but a few hundred.

Under most circumstances you would apply the benefit of the doubt but as the RAT deployed (something there is a lot of evidence for) it strongly suggests this. Yes, the RAT can deploy for other reasons but that would imply an even greater level of coincidence than two engines failing in a short period (3 hydraulic systems, 4 generators, etc.). The distance they went until ground contact also ties in with a loss of pretty much all thrust, as does the audio recording of idling/windmilling engines. There is also the fact, which may turn out to be an assumption, that any failure of other aircraft systems should not affect engine operation as a) the engines are effectively self-powered in flight and b) the engine controls on the flight deck are part of an isolated system powered by the FADECs.

I would be very surprised if the thrust levers were not firewalled early on, in fact with such determination that they went through the instrument panel!

On a wider observation, professional commercial pilots like the Air India ones in this accident go through regular simulator training according their own SOPs, which when dealing with things like thrust loss during or after the takeoff roll are likely pretty similar or even identical to the manufacturer\x92s guidelines; if they did differ it would be because they were more conservative in application. Boeing standard is to do nothing until 200\x92AGL other than control the aircraft in yaw, pitch and roll. Above 400\x92AGL you can start doing some drills, if applicable. This assumes, of course, that you can get to these heights in the first place.

I would put forward that in this accident, the crew immediately found themselves in what Boeing call \x93Special situations\x94 or \x93Situations beyond the scope of normal procedures\x94. We don\x92t know yet whether there was a thrust loss or total failure at the outset; we don\x92t know if the RAT deployed due to sensed failures or control operation. As a trainer, the captain would have known the implications of actioning the dual engine failure memory items, especially near the ground, but if you\x92ve tried everything else and are still going down then what is there to lose? This is not to suggest this is what happened, just to fill in the blanks in terms of possibilities. Whatever did occur likely put them outside the realm of SOPs in short order, which is a difficult situation at the best of times, especially as for your whole flying career you have been trained and assessed at your ability to conform to those SOPs as accurately as possible in the takeoff phase.

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. ]

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 .

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.

Hello, this is my first post on pprune; as a 787 pilot I’m also puzzled by this accident. All seem to agree that for some reason there was a complete electrical failure and RAT deployment. With a complete electrical failure all six main fuel pumps fail. Each engine also has two mechanically driven fuel pumps. On takeoff, if there is fuel in the center tank, it will be used first, pumped by the two center tank pumps.
My airline’s manuals don’t go into much detail, but I read on another site that if both the center tank pumps fail, the engine driven pumps aren’t able to suction feed well enough from the center tanks to sustain engine operation. If there was fuel in the center tanks, a complete electrical failure would soon lead to center tank fuel pumps failure (all fuel pumps failure as stated previously) and fuel starvation of both engines. A rescue from this situation would be an immediate selection of both center tank fuel pumps OFF (not if my airline’s non-normal checklists) and waiting for successful suction feed from the L and R main tanks to occur, this would take a number of seconds.

Great first post (IMMHO!) If this is correct, then I think you are onto something very significant. No expert, just an outside the box thinker who has been trying to see what ordinary (non-pilot-blaming) explanations there could be for a near simultaneous dual engine failure. I imagine a complete electrical failure leading to fuel starvation from lack of pump feed pressure from the centre tank would not result in apparently near simultaneous engine failure, but who knows? (Aren't there (suction) bypass valves here, but maybe they get stuck after long non-opening - instead long subject to closing pressures?) This could have been the case here as my experience suggests the probabilities aren't small.

FWIW, according to earlier posts, the fuel load was about 50T, leaving about 18T in the centre tank, so (I think) about 25-30% full. A full centre tank might allow engine pump suction to work fine, but this might not? (Contrary to what some have said.)

Anyway, FWIW, not everyone agrees with RAT Deployment - see recent post by shep69. Would love to know why he doesn't go with RAT deployment...

Sorry but that doesn't really make sense. Once the power failed and all pumps are off where is the point of switching of the center fuel pumps off? Without power they aren't running anyways.
Furthermore the preference of the center tank while it's filled is just by the higher fuel pressure those center pumps deliver. There is no valve that controls that, which might be triggered by switching off pumps.

I am not a Boeing pilot, but a Bus pilot. I believe that what you're describing is prevented by the certification regs for transport category airplanes.

On the 320 (equipped with the old system (fuel pumps), not the newer system (transfer valves)) the center tank pumps are inhibited when the airplane is airborne with the slats extended.

Check these certification rules:

https://www.ecfr.gov/current/title-14/section-25.953
and
https://www.ecfr.gov/current/title-1...-25#p-25.903(b )

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)

Crossky, welcome to this hamster wheel.

If you go and chat to the engineers, have a look in the IPC or MM I Ch 28, you should find a good description of the fuel boost pumps. It's been a while but I recall they are Eaton designs, the general arrangement is similar to the B777. They both have a suction feed that permits fuel feed in the event of a loss of all boost pumps. The only impact of that arises at high altitude and high thrust levels, where the engine driven fuel boost pumps may capitate and reduce the available fuel feed resulting in a lower thrust level.

Refer page 12.20.02 in the TBC's B787 FCTM, or search for "SUCTION FEED".

At sea level, full thrust will be achieved without any boost pump on the aircraft. Recall that the CWT boost pumps are known as Override boost pumps, they are feeding from the CWT when there is fuel and they are running, as the output pressure is higher from these pumps than the 2 wing boost pumps. Whether there is fuel in the CWT or not, or the CWT pumps are energised, is immaterial to whether fuel will be supplied to the engine driven fuel pumps.

Note that with BA038, the fundamental problem was blockage of wax/ice formed in the piping that blocked the FOHE, and that will cause a problem with those engines that have such architecture, but is not associated with the availability of the boost pumps themselves. Even then, the engines did not technically fail, as they have both done simultaneously with the B788 of AI 171, BA's engines were running but not able to provide significant thrust due to the FOHE blockages.

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.

Just to summarize. There appears to be fairly wide consensus as to what happened:

1. Up to V1 it appeared normal and the pilots did not abort.
2. Loss of thrust very close to V2 rotate or shortly thereafter.
3. Loss of electrical and hydraulics resulting in deployment of RAT seconds after being airborne.
4. Mayday transmission seconds after takeoff (although it may have occurred around V2, the timing has not been established).
5. Gear tilted forward suggesting gear retraction was initiated but not completed.
6. All followed by glide to impact from AGL of little more than 100 feet.

Why the above happened is rather less clear. In my opinion, fuel contamination/starvation, water, additive, vapour or otherwise, may have affected thrust during takeoff before resulting in total loss of thrust and electrical power. On the other hand, software/electrical fault would more likely have resulted in a sudden loss of the engines.

On that basis, there is still some mileage in establishing the aircraft speed in the last moments before takeoff. There is definitely mileage in identifying a single point of failure that would cause the engines to shut down; other than fuel contamination/vapour issues. I suspect that the official investigation is not all that further ahead of this thread. Without useful data from the EAFR they have to rely on forensics and history. Enough has been leaked to know the engines were no more than windmilling at impact.

A high level of interest will continue given there are still remaining questions whether the reliability of Boeing machinery is implicated. That is not to mention the hundreds of people closely affected by this tragedy that are looking for reasons why it happened. Perhaps an interim report is now overdue?