Posts about: "RAT (All)" [Posts: 607 Pages: 31]

You need to read the previous posts. We are NOT relying on ear witness's alone, 2 independent PPRUNE folks did detailed audio comparisons and the evidence is compelling. Plus people close to the Boeing test airfields in the US who have heard RAT tests 500+ times. The RAT was out, that's a 99% certainty. What else would make a sound like prop blades getting close to or perhaps exceeding the speed of sound?

I told you this re translation 3 days ago but the post was deleted then again 2 days ago see post 993.
Notwithstanding the possibility that recollection of the traumatised survivor may be unreliable it seems clear that he thought the engines were spooling up before impact. I think he deserves the benefit of the doubt that he might be right.

Possible auto relight but too late?

May I make a friendly suggestion - might be best to avoid putting in our own interpretations/perspectives of what he said - for example, he doesn't mention "sound" anywhere - we would interpret 'sound' based on experience, but that isn't quite what he said - he only used the word 'race' (a.k.a 'revved' elsewhere). Another example would be interpreting that he said "we were still in one place & not moving" - what he really said was that it felt like they were "stuck" - his word, nothing about movement or standing still or one place. A third one would be 'green & white lights came on in the cabin as we hit something' makes those two events very close together or simultaneous, when his narrative doesn't actually do that, just that they hit something in the end, and before that they 'gave race', and before that a green & white light came on.

To break down the survivor's narrative into an interpretation, am including below a transliteration, direct translation, and the interpretation.


The survivor is a very fast speaker, so had to slow the video down to 0.5x through X's settings menu on the video to capture everything he said.

Video from 1:32 - 1:56

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Transliteration:
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Takeoff ke baad, ek minute ke andar hee, jab takeoff hua naa, to suddenly paanch das second kaise lagaa jaise stuck ho gaya woh. Baad mein (sirf mere ko???) lagaa kuchch hua, baad mein plane mein light on ho gayee, green aur white. Baad mein woh pata nahin woh plane takeoff jyadaa karne ke liye woh race, (do?) bolte hain kya, race diya waisa kuchch, woh seedha (re?) .. speed mein hee ghus gaya, jahan woh, woh (l??), kya tha woh

1:57
Reporter: woh hostel thaa ek, hospital ka

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As direct a translation as feasible without significant rewording or putting in my own perspective on his wording:
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After takeoff, within one minute, when takeoff happened, then suddenly 5-10 seconds what I felt like it got stuck. After, (only to me???) it felt something happened. After, in the plane, light came on, green & white. After, I don't know, to make the plane takeoff more they race, what do they say, gave race, something like that, it straight (1/2 spoken word 'race'?) in speed got into, where, what, what was it

Reporter: it was a hostel, of the hospital

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Less literal translation, more intepretation:
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After takeoff, within a minute, when takeoff occurred, then suddenly for 5-10 seconds it felt like it was stuck. After, it felt like something happened. After that, in the plane, a light came on, green & white. After, I don't know, to make the plane takeoff more they raced, what do they say - gave it race - something like that; it straight, with speed entered into, what was it -

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Later on he describes the mechanics of his escape, and how he was able to get out through a broken door because there was some space on the outside on the ground floor where he landed, and on the opposite side there was a hostel wall that might have prevented others getting out.

Hopefully this might be somewhat useful, even if to only lay to rest some of the theories based on mistranslations of what he said.

It certainly helped me understand that the timeline here doesn't have enough information to line up his description of in-flight events with what's on the external videos.

For example, using the cctv video for timing, his 5-10s lines up with the takeoff and climb from 00:18 to 00:27, and the "felt like it got stuck" part could correspond to 00:28-00:31 where the aircraft appears to 'stop climbing and float horizontally, very little descent' as compared to after 00:31 when it's visibly descending.

The 'something happened' could be the RAT coming online (bang?) but we don't know because there isn't enough detail. Is the RAT even audible inside the cabin? And then the green & white light could be the ceiling light or the exit sign, we don't know, but there is definitely no flickering mentioned.

The 'giving race' part is mystifying - see earlier discussion in the thread - was it changing pitch in the constant-speed RAT due to declining airspeed, something else, engines spooling up? we just don't have enough info here. When did they 'give race' within that 17s descent from 00:31 to 00:48 impact? If we knew that it might help, but that detail isn't there in his description; not surprising since it was a short descent. I think we have to wait for the data from the recorders, or another external video, or maybe even a video from the cabin if somebody was live-streaming to facebook/instagram/x etc.

The Times article also helpfully informs us that

"The [RAT] is not intended to provide enough power and controls for an aircraft to climb after take-off, merely to give minimum control for an emergency descent from altitude"

There was a comment very early in the thread (couldn't locate just now so assume hoovered up by the hard-working Mods) where someone postulated that the late "flare" we see in the video was possibly a pitch-up moment as the engines relit and the pilots went from a glide to a climb posture.

I don't want to review the video again -- personally, I suspect the "revving" the survivor heard was the sound of the RAT spooling up, and that the pilots were flaring as the ground approached in the vain hope of setting her down gently. Just sharing the OPs suggestion as it relates to your comment

Having followed this thread since the beginning, it is clear to me that this discussion is tainted by the fact that many contributors have MCAS and Boeing quality issues at the front of their minds.

I perfectly understand that, so no judgement from me, but it no doubt causes confirmation bias with conclusions being made about extremely improbable outcomes (dual engine failure at the same time during rotation/take off).

The RAT being deployed does not prove a TCMA-failure on both engines nor does it prove that both engines failed (its still not disproved or proven if it was manually deployed).

Extremely fast taxi!

Engineering function. You literally push the RAT guarded switch to on

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

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

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

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

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

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

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

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

Thank you to the mods for an excellent job.

What you are saying is, as several have said before, is that everything started to fail at or shortly before rotation. Joining the dots from two other branches in this thread is it correct to say that there are only two things that happen at that point: the aircraft transitions from "ground" to "air" (multiple sensors) and there is a change in orientation such that any liquid (eg potable water) that has found its way into the EE bay will move. Question: the aircraft was routed DEL-AMD-LGW. Where was the potable water tankage topped up? Presumably prior to the longest sector? In addition to the inspection list that the Indian AAIB has mandated should they also inspect peer aircraft for EE bay corrosion...?

This doesn't make any sense. The plane was in the air for approximately 30 seconds, the plane stops climbing around 12 seconds after take off, and the noise of the RAT is heard 11 seconds before the plane crashes - even if we assume the RAT both deploys instantly and deployed the exact moment that video began recording, that only gives the pilots a 7 second window to perform an action that results in it being deployed.

There just isn't enough time for the RAT to be deployed as a result of any action by the crew, IMHO. And to demonstrate how long 7 seconds is - that's enough to say 20 words, assuming no interruptions .

If you read the thread, you would know:

The RAT was almost certainly deployed. 4 different sources.
The Flaps were not retracted. Visible at the accident site plus many other sources agreeing they were indeed down.
APU will autostart when all engine power is lost. Potentially explaining why the inlet door was open or partially open at the accident site. Mentioned in several previous posts
On a 787-8, the main bogies tilt as the 1st action of the gear retract sequence. As stated in previous posts. I don't think this happens unless gear is selected up. So the conclusion was, gear was selected up. One caveat, IIRC, there was some discussion around a failure could have caused the bogies to tilt without Gear up being selected but I don't recall the outcome.
As for the Air France remark, un-necessary IMHO. Let's respect the crews please.

OK, I promised some informed speculation when I got back, so here goes:
Disclaimer: never worked the 787, so my detailed knowledge is a bit lacking.

First off, this is perplexing - especially if the RAT was deployed. There is no 'simple' explanation that I can come up with.

GEnx-1B engines have been exceptionally reliable, and the GE carbon composite fan blades are very robust and resistant to bird strike damage (about 15 years after the GE90 entry into service, I remember a GE boast that no GE90 (carbon composite) fan blades had needed to be scrapped due to damage (birdstrike, FOD, etc. - now that was roughly another 15 years ago, so is probably no longer true, but it shows just how robust the carbon composite blades are - far better than the more conventional titanium fan blades).

Not saying it wasn't somehow birdstrike related, just that is very unlikely (then again, all the other explanations I can come up with are also very unlikely ).

Using improper temp when calculating TO performance - after some near misses, Boeing added logic that cross-compares multiple total temp probes - aircraft TAT (I think the 787 uses a single, dual element probe for aircraft TAT, but stand to be corrected) and the temp measured by the engine inlet probes - and puts up a message if they disagree by more than a few degree tolerance - so very, very unlikely.

N1 power setting is somewhat less prone to measurement and power setting errors than EPR (N1 is a much simpler measurement than Rolls EPR) - although even with EPR, problems on both engines at the same time is almost unheard of.

The Auto Thrust (autothrottle) function 'falls asleep' at 60 knots - and doesn't unlock until one of several things happens - 250 knots, a set altitude AGL is exceeded (I'm thinking 3,000 ft. but the memory is fuzzy), thrust levers are moved more than a couple of degrees, or the mode select is changed (memory says that last one is inhibited below 400 ft. AGL). So an Auto Thrust malfunction is also extremely unlikely. Further, a premature thrust lever retard would not explain a RAT deployment.

TO does seem to be very late in the takeoff role - even with a big derate, you still must accelerate fast enough to reach V1 with enough runway to stop - so there is still considerable margin if both engines are operating normally. That makes me wonder if they had the correct TO power setting - but I'm at a loss to explain how they could have fouled that up with all the protections that the 787 puts on that.

If one engine did fail after V1, it's conceivable that they shut down the wrong engine - but since this happened literally seconds after takeoff, it begs the question why they would be in a big hurry to shut down the engine. Short of an engine fire, there is nothing about an engine failure that requires quick action to shut it down - no evidence of an engine fire, and even with an engine fire, you normally have minutes to take action - not seconds.

The one thing I keep thinking about is someone placing both fuel switches to cutoff immediately after TO. Yes, it's happened before (twice - 767s in the early 1980s), but the root causes of that mistake are understood and have been corrected. Hard to explain how it could happen (unless, God forbid, it was intentional).

And this just highlights the difficult decision faced by moderators when trying to reduce noise on a thread because, without this additional supporting information , I too raised an eyebrow over the claim of hearing hundreds of RAT deployments.

NOT especially getting at you slacktide , indeed thanks for the followup and presenting your experience/reasoning, however, to assist everyone, including *relevant* background/support detail with one's post is to be encouraged! If you don't have this, or are just speculating from a position of little experience or knowledge, maybe the best contribution would be to sit on your hands for a bit and learn from others?

FP.

I\x92ll reply to my own post in light of the RAT deployment. If true then this opens up to a lot more. And simply guessing with grainy video a fools game. All I saw was gear down to high Into the climb. This should not happen under any circumstance . Dual engine failure would explain the loss of lift obviously. Early flap retraction also. One would hope it\x92s not a simple as that: cheers

Not 757 - it was a 767. Second time it happened in about 12 months.

Determined to be an ergonomics problem with the switch layout in the flightdeck.

Early 767s (JT9D and CF6-80A) had a supervisory "EEC" (Electronic Engine Control - Boeing still uses "EEC" to identify what most people call the FADEC on modern engines). The procedure if an EEC 'failed' was to switch both EECs off (to prevent excessive throttle stagger - unlike FADEC, the engine could operate just fine with a supervisory EEC failed).

Problem was that the EEC ON/OFF switch was located on the aisle stand - right above the fuel cutoff switches. Turned out 'muscle memory' was when the pilot reached down there, it was usually to turn the fuel ON or OFF - which is what they did. Fortunately realizing what he'd done wrong, the pilot quickly restored the switches to RUN and both engines recovered. And yes, they continued on to their destination (RAT was still deployed since there is no way to retract it in-flight).

Previous event was with JT9D engines (United IIRC). In that case, only one engine recovered (second engine went into an unrecoverable stall), they simply came back around and did a single engine landing.

Realizing the ergonomic issue, the EECs were relocated to the pilot's overhead (retrofit by AD).

To the best of my knowledge, there hasn't been a repeat of an inadvertent dual engine shutdown since the EEC switches were relocated. It's also very difficult to 'accidentally' move the switches as there is a locking detent - the switch must be pulled out slightly before it can be moved to CUTOFF.

Sorry but you are wrong. The RAT was basic on the 767 - every single 767 built has one. The Gimli glider deployed the RAT (1982), and the Delta dual engine shutdown out of LAX deployed the RAT.

On item 1, the TCMA issue should have been fixed, it does fit the sort of issue that occurred here. TDRACER can talk to that, and has done in 2019 and again in post 792. As to flap auto retraction, the B787 like all Boeings has a gated flap lever, and the flaps are only able to move independent of the lever by flap load relief. That would not have caused a loss of thrust, and in this case it is evident that the event is a thrust loss not a CL loss.

On item 2, the video shows no asymmetry at any time, so there is only a symmetric failure of the engines possible. Back on a B747 classic, you could chop all 4 engines at the same time with one hand, on a B737, also, not so much on a B777 or B787. I would doubt that anyone used two hands to cut the fuel at screen height. Note, there was a B744 that lost one engine in cruise when a clip board fell off the coaming. Didn't happen twice, and it only happened to one engine.


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Neila83 is correct, the gear tilt pre retraction is rear wheels low, and at the commencement of the selection of the retraction cycle (generally), the first thing that happens is the inboard MLG doors start to open below the wheel well and then the bogie is driven to front wheels low. (There is also an option that the inboard gear doors start to open early as a result of WOW sensing to improve the SSL climb limit). [my bad, for the B788 Capt Bloggs informs us the gear door sequence is after the tilt, not before, the B789 has the before tilt, the option for the door open at rotate is separate]

The inboard doors do not appear to have opened in this case, yet, the gear is forward wheels down. This appears to be out of sequence. TD may have better knowledge on the options that exist with the B788, but this is not looking good at this time.

There is enough in the way of anomalies here to end up with regulatory action, and airlines themselves should/will be starting to pore over their systems and decide if they are comfortable with the airworthiness of the aircraft at this moment. A latent single point of failure is not a comfortable place to be. Inhibiting TCMA might be a good interim option, that system could have been negated by having the ATR ARM switches....(Both)... ARM deferred to the before takeoff checks. The EAFR recovery should result in action within the next 24-48 hours. Boeing needs to be getting their tiger teams warmed up, they can ill afford to have a latent system fault discovered that is not immediately responded to, and the general corporate response of "blame the pilots" is not likely to win any future orders.

I think we are about to have some really busy days for the OEM.


Not sure that Neila83 is that far off the mark at all.

Speaking as a B787 Captain..... There is so much rubbish and stupid suggestion being written here.

This aircraft was airborne for a grand total of 22 seconds, half of which was climbing to no more than 150' aal.

- No Flaps? Due to the setup of the ECL it is physically impossible to go down the runway without some sort of take-off flap set. The T/o config warning would have been singing it's head off. Despite assertions to the contrary I have seen no video clear enough to detect a lack of flaps.

- RAT out? Almost impossible, I have seen no quality footage that definitively witnesses the RAT being out. Those who think they car hear a RAT type noise might be listening to a motorcycle passing or similar. It takes a triple hydraulic failure or a double engine failure to trigger RAT deploment. They happily went through V1 without a hint of rejected take off so as they rotated the aircraft was serviceable. These are big engines, they take a long time to wind down when you shut them down. I have never tried it however engine failure detection takes 30s or for the aircraft to react and they were not even airborne that long.
- Flaps up instead of gear? The B787 flaps are slow both in and out. Given that the 'Positive rate' call is not made the second the wheels leave the ground, a mis-selection of flaps up would not cause any loss of lift for at least 20 seconds, by which time they had already crashed. I believe the gear remained down not because of mis-selection but because of a major distraction on rotate.

Discounting the impossible, two hypotheses remain:

1. Invalid derate set through incorrect cross-checking. Trundling down the runway takes very little power to reach Vr. It is only when you rotate that you create more drag and discover that you do not have sufficient thrust vs. drag to sustain a climb. Or....
2. Put 200' as the altitude target in the FCU. Immediate ALT capture and all the power comes off. PF is still hand flying trying to increase pitch but is already way behind the aircraft.

It could be after this that Boeing are forced to review the B787 practice of exploring the very edges of the performance envelope.

I have to agree with everything here except your assertion about engine shutdown.
Even though these are big engines with plenty of inertia, when you select engine shut off they spool down very quickly if on load. IE, The generators, two per engine and hydraulic pumps, etc, being driven by the (relatively) small mass of the N2 rotor will drag the speed down very quickly, the gennies will trip offine in seconds, the pumps will quickly reduce flow and pressure.
As for what went wrong.
If the engines have stopped working there has to be a common failure mode, fuel is one but as has been said, no other aircraft has had a problem, as far as we know. FOD? It would have to be something major to shut down two GeNX engines and there would be debris all over the runway, we would know by now.
I have no idea if the RAT has deployed, I can't see it in the video and the noise could be something else.
We shall see.
There is compelling evidence that flaps are set correctly and not retracted inadvertently.
I await further evidence.
Edit to add. LAE 40 years, type rated on 737 to 787 with lots of others in between.