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

From the detail in this video:

" Just a short video of the Boeing 787 RAT being driven by an attached hydraulic motor. This test is performed to check the RAT's hydraulic pump and electrical generator are functioning correctly. The motor that is bolted onto the back of the RAT is driven using an external hydraulic rig that is feeding the motor with hydraulic fluid at 4200psi at 40GPM ."

FP.

"I might see a small puff of smoke and a smoke-ring just before they pass the shed."

I originally wondered about that ... until an old colleague sent me this short clip of a triple kicking up dust rotating in the same location

For your consideration: (20 second clip)

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?

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:
------------------

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 -

------------------

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.

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.

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.

Something that occurred to me after I went to bed last night: My assumption that the FDR readouts would rapidly reveal the cause may be flawed.

Let me explain.

The consensus is that both engines quit shortly after liftoff (that assumes that the RAT did in fact deploy). At least one of the data recorders has battery backup, so it should have kept functioning when all aircraft power was lost.

However...

Over the years, I've looked at lots and lots of digital flight data recorder outputs when investigating some sort of incident or other engine anomaly, So I have become rather familiar with some of the interesting characteristics of DFDR data.

On the 767 and 747-400, when you shutdown an engine and the IDG goes offline, there is a momentary 'glitch' in the electrical power system as it reconfigures for the available power source - this is why you see the flight deck displays flicker and return, and the cabin lights momentarily flicker. As a result, most of the avionics boxes 'reset' - this is quick, but it's not instantaneous. This shows up in the FDR data - sometimes as 'no valid data' for a few seconds, or as garbage readings of zero or 'full scale'. Now, looking at the FDR data, it's easy to simply disregard the data, so normally no big deal.

Starting with the 777 (and on the 787 and 747-8), this electrical power glitch was 'fixed' - there is slight delay (~quarter of a second IIRC) before the fuel cutoff signal is sent to the engine - during which the electrical system reconfiguration takes place so no more 'glitch' during a normal engine shutdown...Except whatever happened to these engines wasn't 'normal'.

If there is a fuel cut at high power, the engine spools down incredibly rapidly - a second or two from max power to sub-idle. Assuming the fuel cut wasn't commanded by the flight deck fuel switches, the electrical system won't know it's coming, so it can't reconfigure until after the engine generators drop offline - and you're going to get that power glitch. Nearly every avionics box on the aircraft will reset due to this electrical glitch, and the FDR isn't going to get useful data for a few seconds (and then, only from the stuff that's on the battery bus).

Whatever happened, happened quickly - it's quite possible that whatever initiated the high-power fuel cut didn't get recorded.

tdracer:

"What sort of 'confirmation' do you have in mind - the regulator mandate that resulted in TCMA basically says we can't take credit for the flight crew"

I had just that in mind, as any automated action that could shut down both engines really should have pilot confirmation, imho, but looks like the regulators may not have considered all possible scenarios.

Another question, maybe a complete red herring: Is the TCMA a completely self contained module with it's own processor and software, (possibly the best option) or is it part the FADEC software package, perhaps just a task in a real time multitasking system ?. If the latter, that would open a whole rabbit warren of possibilities.

From all the evidence thus far, it looks like the RAT did deploy, plus other data, which means there was likely a complete electrical power failure. The idea that all four generators and controls would fail at once doesn't make sense, so that doesn't leave much else as the next step.

True, I would bet that the voltage regulating architecture of the voice recorder at least will give useful information for a short time around the loss of power, as it did for the Lockerbie CVR using far less sophisticated recorder systems. That was sufficient to show the pressure pulse in the fuselage and to give a fairly good idea of where the explosion had emanated from. TWA was similar, a bigger bang though. Would be listening for any mechanical noises related to the fuel switches, and frankly I doubt that they existed, but they would be recorded.

If the cause is what I have suggested it will dificult to get direct evidence of that case, as it was for the QFA072 event as well. Like icing cases, a water ingress into the avionics is going to be a tough investigation, water would have been sprayed all over the wreckage in the aftermath. Dousing the E/E bay with 20 or 30 gallons of water will be an expensive investigative exercise to do in a real plane, with engines running. Would not want to be observing up close.

I'd like to mention something that, while unrelated, does shed a bit of light on how computerised systems can misinterpret input data and take the wrong action. I spent 40 odd years as an electronics engineer involving complex systems, it can be surprising just how careful one must be in systems that sample data and then process it for decision making in software.

On August 9th 2019, there was a significant grid failure in the UK leading to load shedding (removing supply to many consumers, including Newcastle Airport) which started when a series of several lightning strikes in Hertfordshire caused a trip out of generators at Little Barford combined-cycle gas turbine generation plant. This was followed by the shut down of the power concentrator and grid connector from the Hornsea1 off-shore wind farm, significant changes in the grid frequency away from the acceptable limits which is what triggered further load shedding.

The reason I mention it is that Hornsea1 going off line was due to the software that operated the concentrator/connector sensing large voltage transients due to the lightning strikes 120 miles away, however these transients were only of the order of 10us length spikes with nominal 20ms cycles at 50Hz on the grid. In old reliable grid equipment that had been in use for decades such spikes would have been ignored because the large rotating machine inertia would make them irrelevant. Other systems went into various states of shut down for protection reasons, some of the Siemens Class 700 trains had to be reset by the train crew, others required a Siemens engineer to drive to each train and reload its firmware. The train protection mode occurred because the grid frequency on the 25kV AC supply went below 49.8Hz, this was a programmed default and it turned out to have been a very conservative one, the trains could have continued to operate normally at even lower frequencies but someone decided to write the programs without actually testing what a sensible limit was. The whole very widespread problems this caused could have been avoided by not acting instantly on microsecond transients in a 50Hz system.

Is it possible that the monitoring systems on a Boeing 787 also sample the electrical system voltages and currents at a relatively high frequency, and thus in the event of a transient of some type perhaps over-react to this event by taking precipitate action instead of waiting a short time before re-sampling again. I have seen a suggestion that an alternative explanation for the "bang" heard by the survivor in seat 11A might have been the sound of a Bus Tie Contactor closing, which in itself suggests something quite important relating to the electrical system. The 787 is unusual in that it uses variable frequency AC generators whose outputs are rectified and then inverted to other AC voltages and also quite high DC voltages, some in the 250-300V region.

I hope that some hard information is going to come out from the investigators soon, but given that the flap mis-selection idea is effectively debunked and we know that the main undercarriage either started its retraction cycle with bogies tilting forwards or that falling hydraulic pressure caused the same thing to happen, then the only thing that fits the observed flight path is loss of thrust on both engines which could have either preceded or followed an electrical failure. We also know that the RAT deployed and in the relatively undamaged tail cone the APU inlet was open or opening indicating a likely auto-start of the APU due to the parameters to trigger that occurring.

I would like to know how many tests of the electrical/computer interactions in 787 development involved arcing/shorting voltage/current transient testing. Is this the sort of thing that is done at all? The EECs (FADECs) in the engines are self-powered via magnetos and self-controlling in many circumstances, but perhaps something caused them to think that the thrust levers had been retarded, and such a thing might have been down to the effect of electrical transients on the various signals received by the EECs.

I have read the original 65+ pages of the thread, but I have not seen any discussion of this particular idea. Maybe that is because the 787 is quite a significant departure from Boeing's previous design practices with totally different electrical systems, higher pressure hydraulics and no doubt other aspects as well.

What do you all think?

I previously speculated the forward truck tilt was proof the gear had been selected UP and the retraction sequence was interrupted.

I’m not so sure now and believe there is a different conclusion from this non-normal gear position.

In normal retraction sequence the gear doors open almost instantaneously after the forward truck tilt. It does seem coincidental the tilt was completed while no indication of the doors opening is visible on the rooftop video, which would suggest hydraulic failure at that exact moment; this precise timing of interruption in the retraction sequence feels unlikely. So is there a more likely answer for the forward truck tilt that does not involve movement of the gear lever?

I suspect it’s more likely that C hydraulics lost power prior to rotation, as a consequence the truck could not tilt rearward during rotation as it normally should. Therefore it’s probable it always stayed in a neutral or forward tilt position from the take off run until we see it in the rooftop video. If the gear was behaving normally, and the crew had omitted to retract, it should be hanging rearwards. Watch any 787-8 takeoff video and you can see at rotation all 4 main wheels stay on the runway as the aircraft rotates. Just after wheels up they tilt rearwards. It’s a very subtle position change.

If the gear was always in a neutral or forward truck tilt position then this undermines the theory that retraction sequence was interrupted. It insinuates the C hydraulic and electrical failure happened prior to main wheels lift off.

For this reason I believe we cannot assume that gear UP was selected nor that retraction was interrupted. I’m seeing lots of social media posts which suggest the forward tilt means gear was in retraction and I don’t believe it was now.

I think the truck tilt position is key to understanding the timeline of system failures and whether the automatic RAT deployment was triggered by power failures or engine(s) failure. The question remains, did loss of center hydraulics happen before or after loss of thrust?

Thanks as always TDR for your excellent professional input. It is therefore so much more perplexing that even you cant logic our way out of this impasse. That is, the assumption that the aircraft experienced a double engine failure (supported by a reasonably convincing argument that the RAT deployed), and yet no plausible reason (that we can see) for such an event. So some then collectively slip into the tired and lazy theories of intentional or unintentional crew actions that 1. beggar belief (intentional), 2. defy physics (flaps instead of gear despite clear evidence to the contrary) and call into question the professionalism of a very experienced Captain and crew as well as the aircraft manufacturer (because...well its Boeing so it must be software ).

Yet, the answer must be simpler and staring us in the face since logic and experience (everything you have offered TDR), tell us that modern airliner engines generally do not just suddenly quit flying at the same time. In this regard we can recall several instances of double engine failure associated with bird strikes generally involving large birds or large flocks or both. But it seems we have discounted this theory very early in discussion. Why? Because we cant see any birds, or flocks of birds or engine flames/surges or puffs of smokes from the engines which would support this. Really?

I have read all the 100's of posts (sadly) and while some very early posters tried to analyze the imagery, I suspect the very poor quality eventually discouraged most from seeing anything of interest. However, smattered throughout this discussion from the beginning to the end there have about four posts that describe seeing something where others have not. At least two of these were related to possible smoke but which were probably just the dust blown outwards by the wingtip vortices. Two others however have mentioned possible flames and puffs of smoke.

The video of course is very poor. There should be a special place in hell for people who subject us to looking at a video with continuous zooming in and out, inability to retain focus on the subject (it was just a CCTV monitor, not the actual aircraft they had to focus on) and constant camera shake. A video of a video, and then the resolution probably reduced for social media upload. This all results in a very unwatchable record of the aircrafts departure. The only immediate information gleaned seems to be some idea of how far down the runway the aircraft was at takeoff and the parabolic curve as it very clearly described the aircrafts flight path.




Air India Flight 171 on departure
But take a look at this frame. The right engine shows an artifact (pixelation if you like) that might represent a surge flame. I can almost see a puff of smoke just inboard of the aileron that may be associated with that too.

Am I just seeing distortion? Am I just seeing some smoke because that's where I would expect to see it?
We are all very used to seeing everything in 4K today but back in the day when everything was low res we used to join the dots. If pixels existed then something was there. If they didn't, it wasn't.
So if it's just pixels caused by distortion then they have coincidentally appeared in the tailpipe of an aircraft that crashed shortly after takeoff with a presumed double engine failure.

But surely we would see the birds? Well, not in this video. You cant even see the registration number on the side of the aircraft and that is much bigger than a bird. Haze, distortion, focus and low res, and each individual bird wouldn't even make up a pixel.

So make of this what you will, but this problem may have started on the ground. Birds strikes are very common according to Some AI pilots who interviewed for this following article but I have no idea of the authenticity of this report:

https://www.rediff.com/news/report/a...h/20250613.htm "The Air India pilots also added that Ahmedabad airport has long been known for bird activity near the runway, which could have contributed to the incident.

"This issue (of the excessive presence of birds) has been flagged multiple times," a third Air India pilot said, asking not to be named."
Of course, a single engine failure would not have brought this aircraft down, nor would it have deployed the RAT, but we can't see what happened on the left engine when the aircraft slipped behind the radio antenna building.

While these high bypass engines are designed and certified to keep running after experiencing certain types of bird strike, the effect on two engines concerns have been voiced about the contribution of certification to the mitigation of the risk hazardous bird strike in the two engine case.

This from Sky Library:
https://skybrary.aero/articles/aircr...nue%20to%20fly .

" A number of concerns have been quite widely voiced about the contribution of certification to the mitigation of the risk of hazardous bird strikes:

• The case of bird ingestion into more than one engine at the same time is not addressed directly and it is clearly extremely difficult to meaningfully estimate the probability of such an occurrence. However, it has been observed that, since some of the current standards only require that a damaged engine can be safely shut down, this circumstance should be more fully considered when determining the acceptable outcome of ingestion into single engines, especially for the twin engine case.
• It has been noted that the potential effects of bird strikes on modern electronic flight control systems and flight deck instrument displays have not yet been fully assessed.

Maybe someone can do some video enhancing of this image as others have done with the audio enhancement to give strong probability of RAT deployment.

If my suggestion can be corroborated at all, then the question of what happened next becomes somewhat easier to answer. Perhaps neither engine stopped running but they did so with limited thrust? If anything from the pilots mayday call can believed, it wasn't engines shut down..it was no thrust. So why did the RAT deploy? Cant answer that. And, I cant imagine it would be manually deployed if both engines were still running.
However, TDR did say.

"On the 767 and 747-400, when you shutdown an engine and the IDG goes offline, there is a momentary 'glitch' in the electrical power system as it reconfigures for the available power source - this is why you see the flight deck displays flicker and return, and the cabin lights momentarily flicker."

Startle factor that electrically systems were about to fail? Manually deploy RAT?

Edit: I might add, they would have found remains on the runway if this did indeed happen. But we have heard anything from anybody?

I originally was onboard with the truck tilt seen in the one video being proof that the gear handle was selected rather than the flap handle. But after watching several videos and an "endless" web search for info, I also have started to think that there was a problem before the gear handle was moved.

In a normal retraction, the main gear doors begin to open before the truck tilt is complete (roughly when the gear trucks are "level", seen around 8-10 second marks of this video ). The nose gear doors open at the same time the main gear tilt starts (seen in Jetstar video linked below). It's too blurry in the video/stills of the accident aircraft to definitively say the nose doors are not open, but I'd say no. And it's pretty much a certainty that the main gear doors are not open. And finally I think it is also pretty clear that the main gear trucks are tilted down to the retract position.

I have no confirmation of this, but I read (or heard someone say in a video) that the truck tilt actuator was a "single acting" actuator, meaning hydraulic pressure held it in the toe up position and it was spring loaded to the retract position. Which means if hydraulic pressure was lost due to loss of power to the electric driven center hydraulic system, then the main gear trucks would tilt forward on their own without moving the gear handle. The Jetstar burst tire video somewhat backs this up, in that the blown tire caused a leak to the center hydraulic system and an alternate extension was required (thus the reason the main doors are down during the landing). No hydraulic pressure means the main gear trucks remained pointing nose down during the landing. Video here

WHEN something catastrophic happens, like dual engine failure, that then creates a query about any "duality" between two standalone systems that really should have nothing whatsoever in common... except the PF.
Nothing in common? Is that really the case for the 787-8 in the Air India 787 crash?
Look at these three TCMA-related links in the order presented and note the proforma prescriptive caveats in the first two:

https://downloads.regulations.gov/FA...tachment_1.pdf
https://downloads.regulations.gov/FA...tachment_1.pdf
https://patents.google.com/patent/US6704630B2/en

TCMA is designed to detect and accommodate single failures within the EEC/FADEC, preventing a failure from jeopardizing the safe operation of the aircraft.
Implementation:
It involves implementing specific software changes within the engine's control system (EEC).
Regulation:
After some incidents, the design change was mandated by regulators, with a deadline for production aircraft by December 31, 2018, and a retrofit plan for existing aircraft.
Boeing 787 Application:
The TCMA feature is specifically relevant to the 787-8 equipped with GEnx-1B engines, but it may also be applicable to other 787 variants using the same engine type.

The first two links are respectively the request for and FAA affirmation/approval for a GENx-1b software system called TCMA (Thrust Control Malfunction Accommodation). TCMA is the system that precludes High Uncommanded Thrust (HUT) after touchdown by fuel-chopping the engines. It is designed to avoid runway departures. One input is power-lever position. It's then fair to say that (additionally) Air/Ground sensing is quintessentially vital (as to when the system is "armed" and can do this fuel-chop). The third link is the complex description (with diagrams) of the patent application's design functionality of TCMA.
FROM THE 3rd link above:
"​​​​​​The method of the present invention compares the engine's actual power level with a threshold contour defined by the TCMA software package. When the TCMA software package determines that a thrust control malfunction has occurred, based on the engine's power level exceeding the threshold contour, the engine is shut down by the TCMA circuit." It is also notable that it says within the 3rd link that "Typically the aircraft is allowed to operate for a limited period of time with just a single operative processing subsystem."
That Air India 787 was not long out of maintenance.
We are then motivated to ask "what dictates the Air/Ground sensing". Is it just a Weight-on-Wheels microswitch or a RADAlt? (or both? or triplicated micro-switches?). We may then ask: "Did Air India implement the post-5G changes to their RADAlts that concentrated on maintaining their auto-land capability (in the face of 5G interference with RADAlts?) I seem to recall that the FAA's dictums on this pointed out that it was an individual nation's responsibility to both control their 5G frequency spectrums and implement changes to Radar altimeters that would work interference-free in critical phases of flight. What has the Indian regulator done in this regard as the responsible entity? The whole shemozzle, starting with the US Federal Communications Commission (FCC) spectrum allocations, was an ongoing fight between the telecom giants and their getting their new mobile tech to market.

So where are we going with this line of causal reasoning? The only commonality/duality between left and right engines is the software driving the TCMA as monitored by the TCMA software incorporated in each engine's EEC. Most pundits have identified the gear-tilt as evidence that only the centre electrically-driven pump can do the gear-tilt if the engines' other two hyd systems are suddenly both in QUIT mode (which accords also with the instant RAT deployment and loud noise heard by the sole survivor) - and an ensuing transition from climb-out to a deadly sinking and commensurate attitude change for speed maint.
My unavoidable conclusion is that the selection of gear UP and the breaking of the gear downlocks (and WOW sensing and energization of the RADALTs) called upon the TCMA to fuel-chop the engines (via the TCMA functionality in each engine's EEC).
We could start by looking at the No Break Power Transfer (NBPT) tech used in modern airliners. This has led to Gen Control Panel meltdowns in 777's due to GEN contact meltdown. I know of one instance when a 773 was reduced to a RAT only landing enroute and another where a disastrous MEC fire occurred after start on pushback at LHR. A description of the systems glitch often experienced is at the following link. It's quite apparently a "gear-up" hiccup with potential damning consequences for smooth TCMA operation. As to be seen in the quality videos, a fuel-chop provides no real clue (such as engine failure/smoke/fire classically does). An uncommanded "reset" of the two engine's TCMA's upon gear retraction (link below) is trackable to be the sought after "duality" leading to a "both simultaneously quit" engine failure. These momentary electrical glitches and instant "resets" are described in the two links below. Food for reasoned thought?

https://tinyurl.com/yn5ce4tz

https://tinyurl.com/3kkh6n3d

One comment here, and maybe I am mis-understanding your comment, but the landing gear only operates via the center hydraulics. It does not matter whether the Left/Right engine driven hydraulic systems are operative or not. The RAT will only pressurize the primary flight control portion of the center hydraulics.
No idea. I only got that info from the Master MEL on the FAA website. According to the MMEL the aircraft can be dispatched as long as there is one of each type sensor working on each main gear. (AIs MEL could be more restrictive)

As a pilot with 40+ years of professional flying, currently on the B777, and with some background in modelling aircraft performance, I've got a few observations, having read all posts.


Flaps & Takeoff

The flaps were out for takeoff, which was normal: normal rotation rate, right place on the runway. Debris also shows the flaps were out at impact. The plane's flight path completely matched what you'd expect from a flight with flaps set correctly.


Flight Controls & Pilot Action

To my mind, the controls were clearly working right up to the very end of that tragic flight. This also strongly suggests the plane never had any asymmetric thrust, because there's no sign of yaw, rudder, or big aileron/spoiler movements. The pilots seemed to guide the plane accurately and consistently, just like an experienced crew would. It looks like they were highly skilled from the start: immediately after rotation, they lowered the nose a bit to keep the plane flying. They also bleed off speed to avoid ground contact. Eventually, with no speed left, the plane descends, but it still looked like they were in control. The instinctive pitch-up right before impact is what a lot of pilots would do.


ANC

Why transmit to ATC ? beautifully described by EGPI10BR


Aviate: The aeroplane has decided it doesn\x92t want to do that any more

Navigate: Not many options on where to go

Communicate: May as well let people know it\x92s going to be a bad day and to get there ASAP.


Booster Pumps

Engines don't actually need booster pumps at sea level to get takeoff thrust. (tdracer)


Restart

There's no noise of the engines spooling up at impact. The mobile phone footage just has the RAT noise, normal airframe sounds, and impact noises. I didn't hear any engine spooling up. That witness talking about a "revving, starting noise" sounds to me like he was trying to describe the RAT noise, which we're all pretty familiar with now.


Engine Spool Down

When I did this for real in an actual plane (we had an uncontrollable engine, but also three good ones), stuck at about 30% maximum thrust, at 220 knots, it was an instantaneous spool-down \x96 really dramatic. The yaw came on so suddenly it felt like a heavy catering truck had slammed into us at speed.


Engines

They appear to get the plane to the correct speed and position on the runway as commanded, then at a time very close to rotate they stop providing thrust. The rest of the flight is consistent with gliding flight.


Rotate vs. Air/Ground Switching Vs Pilot action

(This is my take, it might seem counterintuitive, if you know better help) On a normal takeoff at rotation, liquids don't slide backward any more than they do during the takeoff roll itself. They slide back during the takeoff roll, and at rotation, there's actually a slight reduction in those backward forces. The main force is still pushing them back, but because the wings are now generating lift, there's more drag than when the plane was just rolling on its wheels. So, if liquids have pooled at the back of something at rotation, during and just after that maneuver, they'll actually ease forward a bit. The main force is still pushing them back, but it's less so. My take is if something sudden happens around rotation, I think it's probably more connected to something like the air/ground sensing or pilot action, but it is still possible that pooled liquids sloshing forward a little could also cause it.
Pilots have to do a few things at rotate time, pull back in the controls, not the thrust levers in error and then move the landing gear lever. Over the years there's been a few action slips, so unintended control movements.

Are you saying that the RAT cannot power retraction of the gear, neither via its own hydraulic pump nor via its generator providing power to the centre system pumps?

Or could it be that it's capable of delivering enough power (via either route) to move the tilt actuator but not a humungous retraction jack?

SLF engineer ( not aerospace)
so nothing to contribute but a query. I've read the first thread since it started and then this one and the best suggestions I've seen which seem to fit multiple failures at rotate and shortly after (gear mid cycle or failed hydraulics, RAT out, emergency lights on, lack of thrust) involve some catastrophic failure in the electrical systems. My query is will the investigators be able to establish this, are there environmental sensors in the EE bays which might detect and record water presence (steam, excessive humidity) before there are cascading and otherwise unrelated failures in a variety of systems.
Obviously a long term leak would leave corrosion residue but a recent burst build-up with a dam overwhelmed at rotate might be more difficult.

The RAT provides hydraulic power only to the flight control portion of the C hydraulics. Wing and tail flight controls only. Non return valves prevent power to other C hydraulic powered systems like the gear.

The RAT provides electrical power only to critical flight instrumentation (mostly Captains), navigation and communication. The same critical equipment that the Battery will provide. If all electrics was lost, the main Battery would provides standby power until RAT is fully deployed. The RAT electrical power would not be able to power C hydraulic electric pumps.

Views from outside the box will likely be worthwhile in this case.

Re E/E environmental, no sensors incorporated, and they probably would not help in the type of problem that I have concerns with. The crew get an idea of a problem as multiple systems fail at the same time from water inundation. This is way outside of the DO-160-G requirements taht the electronics are certified to. Pouring a kiddy pool worth of water that is sitting above the bay in the moisture barrier awaiting a suitable opportunity to become evident is outside of expected behaviour, but has happened at least 3 times with major impacts on other aircraft.