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

cncpc
2025-06-14T23:03:00
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Post: 11901937
Originally Posted by A320 Glider
Just to confirm.
The 787 is an aircraft which likes to, performance wise, use all of the available runway for takeoff. Sometimes you can be sat in the 787 and as you are rolling down the runway, you start wondering if Rotate has been called or not. It loves taking up all of the runway.

Nevertheless, there are some interesting speculations over on X. One guy even claimed the Captain was in the lavatory during the accident...

Many people have noted what appears to be the RAT deployed in the video footage suggesting dual engine failure. Possible wrong engine shutdown? But who diagnoses and actions an engine failure and shutdown below 400ft?
The Mayday specified loss of control and engine failure.
fdr
2025-06-14T23:20:00
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Post: 11901949
Originally Posted by tdracer

... The TCMA logic is designed and scrubbed so as to be quite robust - flight test data of the engine response to throttle slams is reviewed to insure there is adequate margin between the TCMA limits and the actual engine responses to prevent improper TCMA activation. Again, never say never, but a whole lot would have had to go wrong in the TCMA logic for it to have activated on this flight.

Now, if I assume the speculation that the RAT deployed is correct, I keep coming up with two potential scenarios that could explain what's known regarding this accident:
1) TCMA activation shutdown the engines
or
2) The fuel cutoff switches were activated.
I literally can come up with no other plausible scenarios.

In all due respect to all the pilots on this forum, I really hope it wasn't TCMA. It wouldn't be the first time a mandated 'safety system' has caused an accident (it wouldn't just be Boeing and GE - TCMA was forced by the FAA and EASA to prevent a scenario that had never caused a fatal accident) ...
TD, in this case, the RT call suggests we are a grand total of 1 choice, and that goes to a fair likelihood that a fleet wide grounding is in the offing. Adding system complexity dependent on sensor reliability has bitten us all in the past and will do again, and I have a bad feeling that is where we are at with this. The SSA guys will be working overtime, but this has had the hall marks of being a bad sensor/system event from the outset. Am laying bets that there will be a fleet wide grounding in the next 3-4 days, if not sooner. Inadvertent GA thrust after landing has occurred before, (had it on a B744 myself), and it is curious but straightforward to handle.

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CriticalSoftware
2025-06-14T23:45:00
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Post: 11901966
Several hundred posts ago, a link to a PPrune thread re 787 RAT deployment was posted. I am sure everyone posting has at least seen if they have read the thread....

I apologise, if my thoughts have already been posted - please delete if this is the case, I cannot find them in the main thread though

None of us know if there was no engine failure, single engine failure or double engine failure.

If RAT was deployed, we do not yet know whether it was automatic or manually deployed by a very experienced captain because "We have no power. What harm can it do now?" (Electrical power, not thrust) Would the Captain also elect to start the APU in the few seconds he had?

In the thread re 787 RAT deployment, some one states that a single engine failure, due to the small rudder size on 787-8, automatically throttles back the remaining engine as the rudder will not be able to correct the course. I am not clear about the guards around this - be they height restrictions, speed restrictions or % of power delivery. If there are any guards in the software. It may have been stated and I missed it or didn't understand.

However, as someone involved with critical software design & development, if the generators were "playing up", which is highly possible given passenger observations on previous flights, could there be a window, if the aircraft experienced a problem with say no 1 engine ( suggested in video "analysis" despite the aircraft tracking right ) whereby the loss of electrical power triggered the software to "throttle back" No 2, and that again limiting any recovery of No 1, if the generators on 2 didn't perform/react as planned. Software always has holes.

The primary flight deck screens have battery backup - but do they lose power when the main buses go offline - and/or again when the RAT delivers? Or is it seemless? Previous posts mention both scenarios but with no answer. Are there flickers, resets, reboots? All distracting at best and time limiting at worst.

I think a pertinent point posted earlier, was that the problems seems to have begun with "gear up", a lot of load on the electrically driven, hydraulic pumps.
Seemingly started, but obviously not completed.

I believe the 2 guys sitting in row 0 dealing with this, were just passengers from the moment it left the gate - for whatever reason. The mayday call, by whichever pilot - although no transcript officially published - was probably a last ditch attempt to alert ATC asap to a situation with a clear outcome. Very sad. It is bad form to point the finger before any useful facts are confirmed.

So, I suspect generator problems & a hole in the software and/or logic due to timing issues caused by generators appearing to be on/offline -maybe rapidly - restricting thrust by design..

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KATLPAX
2025-06-14T23:53:00
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Post: 11901971
Originally Posted by appruser
Have been thinking about this a bit in this thread. First I thought it might be the APU spooling up, but apparently the APU isn't very audible in seat 11A - good 787 sound insulation. Cabin Air Compressors are not started either if power loss induces APU start, so that might not be it either. Since his sequence doesn't give a good idea of when, is the RAT a potential source of this noise? would it be audible in the cabin? Apparently the RAT is variable pitch constant speed, so as the aircraft speed decayed from 170kt to 120kt, would it become louder as the RAT prop pitch adjusted to the lower airspeed?

It's a great question!
if the engines were spooling down, packs down, the ambient noises would be low enough that I would think anything is a possibility\x85
First_Principal
2025-06-15T00:01:00
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Post: 11901977
Further on RAT deployment noise and acoustic analyses

Just commenting on the earlier acoustic analyses of RAT deployment conducted by Kraftstoffvondesibel and myself.

Firstly it will be clear that we posted our respective audio analyses about the same time. There was no collaboration I assure you, and in fact I'd been waiting all day to see if someone else with more recent or pertinent experience than me would do something. When I hadn't seen anything I spent a little time and came up with what I did, however I think Kraftstoffvondesibel's work is probably more useful than mine given their specific plot methodology and that they included a non-RAT 'control' pass. I was in the process of acknowledging this when the thread was closed; late at night for me which is why this post is now some hours on.

At the time I posted I was fairly circumspect for the reasons given but, with the similarities between our results and along with some other detail that's come to light in PM, I am now more persuaded that the acoustic print we both observed is most likely to be from a RAT (although until this is confirmed a question must necessarily remain).

FWIW, and in part answer to a later post enquiring about the noise of a RAT dropping into position, this also aligns somewhat with the survivor's apparent observation of a noise ('bang'?) prior to impact, and an earlier post by DaveReidUK stating that RAT deployment results in a 'humungous' bang.

FP.

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wokawoka
2025-06-15T00:38:00
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Post: 11901997
Sector Crewing

777 Driver for a legacy here.

This is a 10 hr ish sector. Would there not be a 3rd crew on this? There definitely is in my outfit for that length.

I was of the belief of flap mis-selection as I have seen in the past. However, with video fly past noise, the sound spectral analysis, I am happy to be convinced that the RAT was out.

There are only a few scenarios where this happens - electrical malfunction would not cause the engine to shutdown. However the engines shutting down would cause the electric malfucntion depowering the BUS' which activates the RAT. This is a billion to one chance. Can't see it happening.


Last edited by Saab Dastard; 15th Jun 2025 at 20:41 . Reason: Removal of unwarranted speculation

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BugBear
2025-06-15T00:50:00
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Post: 11902002
Originally Posted by wokawoka
777 Driver for a legacy here.

This is a 10 hr ish sector. Would there not be a 3rd crew on this? There definitely is in my outfit for that length.

I was of the belief of flap mis-selection as I have seen in the past. However, with video fly past noise, the sound spectral analysis, I am happy to be convinced that the RAT was out.

There are only a few scenarios where this happens - electrical malfunction would not cause the engine to shutdown. However the engines shutting down would cause the electric malfucntion depowering the BUS' which activates the RAT. This is a billion to one chance. Can't see it happening.
The question, unasked ....

Does TCMA understand WoW prior to taxi!? Taxiing, accelerating? Rotation, Braking, Stowed? Does the software? Does the subset? Who designed it's Contours?
MaybeItIs
2025-06-15T00:54:00
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Post: 11902008
Originally Posted by FullWings
I think it needs to be said again that pretty much anything can happen to the aircraft systems and the engines will carry on running - this is by design as they have independent FADEC and power supplies and at sea level fuel will get through without boost pumps. You could almost saw the wing off the fuselage and the engine would still produce thrust, TCMA notwithstanding.
Yes, thanks, I've seen a few comments to this effect, and I have to accept most of what you say. I understand that they have their own dedicated generators and local independent FADECs (or EECs), but I'm trying to use what I do know to attempt to figure this out. I know that there are Fuel Cutoff switches in the cockpit. Somehow, if switched to Off, these will cut off the fuel to the engines, "no matter what". Of course, even that's not true, as the Qantas A380 engine burst apparently (comment in this thread) showed.

Anyway, the thing I'm looking at is how the fuel cutoff switch function could have been activated in some other way. To me, it seems obvious that there are wires that run between the engine fuel shutoff valves and the cockpit / flight control panel (no doubt with relays etc in between). I don't know where those shutoff valves are located, but logic says they should be located in the fuselage, not out at the engines. I also don't know how those valves operate - are they solenoid valves or electro-mechanically driven? Nor do I know where the power to activate those valves comes from, but using my logic, if those valves close when powered off, such as solenoid valves typically do, then the power cannot exclusively come from the engine-dedicated generators. If it did, you'd never be able to start the engines so they could supply their own power to hold those valves open. So, there must be some power (appropriately) fed from the main aircraft control bus to activate those valves - if the rest of what I'm assuming is correct. Anyway, like I say, I don't know enough about the details at this point, but there are many more ways to activate or deactivate a circuit than by flicking a switch. Killing the relevant power supply, for example. A screwdriver across some contacts (for example), another. Shorting a wire to Chassis, maybe. Just trying to contribute what I can.

You raise another interesting point: "TCMA notwithstanding". Could you elaborate, please? What will happen if the TCMA system, which apparently also has some degree of engine control, loses power? The problem with interlinked circuits and systems is that sometimes, unexpected things can happen when events that were not considered actually happen. If one module, reporting to another, loses power or fails, sometimes it can "tell" the surviving module something that isn't true... My concern is where does the power to the Fuel Cutoff switches come from? Are there relays or solid-state switches (or what?) between the Panel Switches and the valves? If so, is the valve power derived from a different source, and if so, where? Are the valves solenoids, open when power applied, or something else? What is the logic involved, between switch and valve?

Would you mind answering these questions so I can ponder it all further, please? If I'm wrong, I'll happily say so.

Originally Posted by FullWings
We don\x92t know yet what actually triggered the RAT from the relatively short list but every item on it means there is a serious/critical failure(s). The flight path suggests that it was a double engine failure or shutdown (commanded or uncommanded) as anything else should have left the aeroplane in a poor state but able to climb away.
100%

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aeo
2025-06-15T01:21:00
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Post: 11902026
Originally Posted by Compton3fox
It's controlled by Software and I've seen enough very weird "corner case" bugs that I discount nothing when Software is involved. I am sure there are more likely explanations why all power was lost (Assuming that was the case) but nothing would surprise me!
So are we now saying total loss of AC power for the RAT activation and activation of TCMA on two very independent engines for the power loss? What are the chances..

I can buy the AC power loss, but TCMA activation as well - That\x92s a stretch. TCMA is available on the ground and on approach and will activate if the engine thrust doesn\x92t follow the Thrust Lever command. On the ground it will shut the engine down (think RTO with engine stuck at T/O). On approach it will reduce the thrust if the engine doesn\x92t respond to the Thrust Lever command ala Cathay Pacific A330 (CMB - HKG) with the fuel contamination incident.

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bal00
2025-06-15T01:55:00
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Post: 11902044
In this thread there has been a lot of back and forth about whether or not the RAT is visible in the flyover video. I think some of the confusion may stem from the fact that people are watching different versions of the same video. There's a low quality version where someone is pointing a camera at a monitor. This is obviously not good enough to see anything. Then there's a higher quality version that seems to be a direct upload of the video in question. However, because it's hosted on X, there are different versions of that one as well. The player will auto-select the resolution that it thinks is most appropriate for your device, but this could very well be a lower resolution. The highest quality version that I'm aware of is 884x1564. I can't provide a direct link, but if you want to scrutinize the video, I would suggest using a website/app/browser plugin of your choice to download this version first. Don't rely on the X web player.

If people are saying that they can't see anything that looks like a RAT, that may very well be true, depending on which version they're watching.

I don't have the ability to post direct links, but I did take a frame from the highest quality version of the video, and what I see is a RAT-sized, RAT-shaped object protruding from the fuselage in the exact position where you would expect the RAT to be.The image in question has only been cropped and enlarged by a factor of 2. No other editing, processing, sharpening or AI enhancement has been done. If someone else wants to replicate it, the timecode is 00:08.05.

imgur. com/a/YE2q1e3

If someone with link-posting privileges wants to upload the image here, that'd be great.
bakutteh
2025-06-15T02:13:00
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Post: 11902053
Devil Pprune Mind Traps from overwhelming posts

Do not discount the mistaken early flap retraction scenario too easily. Mull on this:

PF commanded gear up on attaining positive rate of climb, fixating on the HUD.
PM mistakenly raise flap lever from 5 to Flap 1 gate. Thrust reduced to Climb Thrust. Landing gear remained deployed. Massive loss of lift misidentified as loss of thrust. If any one pilot just had a dual engine failure scenario on a recent sim ride, brain and muscle memory would jump to loss of thrust in dual engine, prompting them to accomplish the recall memory items which called for both engine fuel control switches to CUTOFF and then RUN, and physically deployed the RAT.

There would be immediate loss of thrust with the engine taking time to recover , if at all, at such low airspeed!
The rest is left for Ppruners’ imagination.😖🥴😬

Last edited by bakutteh; 15th Jun 2025 at 09:18 .

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First_Principal
2025-06-15T02:23:00
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Post: 11902057
Calculation of a/c speed from audio analysis

Further to the audio analysis of a deployed RAT; given an audio print, known noise source [RAT] frequency, location of a receiver and relative location + direction of moving object, and using the principles of doppler effect etc, it should be possible to calculate [ground]speed of a passing aircraft.

Thus, having been informed that the source frequency of a RAT is 145Hz (thank you that person - please ID yourself if you wish), and with regard to the [assumed] RAT acoustic print available for AI 171 we are close to being able to determine an approximate airspeed during descent (given the video from which we get this acoustic data appears to start during the descent).

There are several variables in play here that we don't know exactly (the positions of observer and aircraft, height agl of observer and aircraft etc), and some I will ignore for the moment (effect of air temperature/pressure for example) but if one makes an educated assessment from the visual cues in the video I calculate an initial relative airspeed of circa 120kn. Necessarily this is an extremely rough number, in fact the range (making various positional assumptions etc) appears to be between ~100kn to ~150kn, but if it turned out be either side of this I wouldn't be completely surprised.

As with the initial audio analysis to determine whether a RAT was deployed or not I offer this for those to whom this sort of data may be important. Not sure if it's of any real use or not, and I wouldn't hang your hat on it, but here it is in case it assists. Should it matter I expect some sort of corroboration could be obtained by making an assessment of vertical speed from the variously available videos and extrapolating from there.

My previous caveats over veracity of source data etc remain.

FP.

Last edited by First_Principal; 15th Jun 2025 at 03:17 . Reason: Update range upon further analysis - remains difficult to determine accurately

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Lifer01
2025-06-15T02:29:00
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Post: 11902059
Originally Posted by Someone Somewhere
I can't see how gear pins would stop you doing anything more than raising the gear. They don't cause engine failure, RAT extension, or uncommanded flap retraction.
I'm sure it's not the case, but if an attempt was made to raise the gear with the pins still fitted, you would see the main gear doors open as part of the normal gear retraction sequence.

This applies equally to a normal gear retraction: the centre hydraulic pumps must have stopped very early for the trucks to be in that position on an "interrupted" gear retraction, with the main gear doors still closed (and presumably locked). Seems unlikely.

Originally Posted by Someone Somewhere
I did raise this earlier... FCOMs say that the bogies remain in the stowed tilt after a gravity drop, but I don't know if that's because the gear has springs to hold it that way without hydraulics, or just they close the valves on the hydraulics so it stays in the last commanded position without pressure.
The tilt and stow positions are definite hydraulically achieved positions of the truck positioner actuator. I don't think the actuator is spring-loaded to the stow position on the 787, though perhaps they move that way given my earlier statement...

Alternate extension appears to rely on the truck positioner remaining in its previously "positioned" state - stowed - where it has been sitting cold, unloved and unpowered since the gear was previously retracted. Like other Boeing types, the wheel well has some bars to stop the truck moving while it's up and stowed.

It's remotely possible the main gear priority valves may have prevented more gear movement in the absence of good hydraulic pressure - however this wouldn't stop the nose gear from operating, so not likely.

Last edited by Lifer01; 15th Jun 2025 at 02:39 .

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BrogulT
2025-06-15T03:21:00
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Post: 11902071
Question

Originally Posted by bakutteh
Massive loss of lift misidentified as loss of thrust. If any one pilot just had a dual engine failure scenario on a recent sim ride, brain and muscle memory would jump to loss of thrust in dual engine, prompting them to accomplish the recall memory items which called for both engine fuel switches to OFF and then RUN, and physically deployed the RAT.
I keep reading this theory and I'm baffled. You think the PF is going to attempt a dual engine shutoff and relight during the initial climb based on a hunch that the engines have quit, all without even a sideways glance to see what N1 is or a short word with the PM?

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Smooth Airperator
2025-06-15T04:47:00
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Post: 11902101
Originally Posted by BrogulT
I keep reading this theory and I'm baffled. You think the PF is going to attempt a dual engine shutoff and relight during the initial climb based on a hunch that the engines have quit, all without even a sideways glance to see what N1 is or a short word with the PM?
I don't want to believe it either. It defies belief but given certain confirmation bias (sim), panic and inexperience by the FO, it's not beyond the realms of possibility. It explains both the RAT and loss of lift. The alternative right now is a catastrophic electrical failure that wiped out the engines or engine control leading to loss of thrust, or a dual engine failure due to birds, fuel contamination or FOD. They are also valid, though IMO less likely.

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Someone Somewhere
2025-06-15T04:53:00
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Post: 11902102
Originally Posted by MaybeItIs
Ok, thanks for clarifying. Of course, an overload will simply cause the hydraulic pressure relief valves to activate. There will be a moderate increase in motor current when bypassing, but the electrical side should be fully able to cope with that. Should be! I'm suggesting here that there was a fault somewhere in the electrical supplies that effectively derated some part of it, and that maybe the GearUp load was too much for it on this occasion.
This is a constant-pressure hydraulic system, not a little hydraulic ram on a logsplitter. While I assume there are some overpressure relief valves, they're not relevant here.

It uses a variable displacement pump to maintain 5000PSI constant pressure. The swashplate angle is varied to adjust pump output flow: more devices consuming fluid, more flow to keep the pressure up. If the pumps cannot deliver enough fluid, the swashplate reaches the full flow position and the output pressure decreases until flow consumed equals flow produced. Very much like a constant-current constant-voltage power supply.

Running in that area of maximum flow is 100% expected under some conditions, especially if an engine or EDP fails and the electric demand pump is supplying a whole hydraulic system sized for the larger EDP (although I think this would be less of an issue on the 787 as the L/R systems don't do much, but the same variable-displacement pump design has been around for a LONG time including on the 737).

And again, there's a VFD between the aircraft electrical bus and the pump motor, because the pump is 400Hz and the aircraft is wild-frequency. VFDs are very very good at isolating faults unless you are actually looking at a sustained overload on one of four generators .


Thanks for confirming the 4 gens. So there's probably quite a bit of switching required. Not sure how that's done, but I guess robust contactors are required. And even these can fail. Systems usually cannot tell that a contactor has failed on the open side until it's switched. So, a switchover may have been done, but a failed contact meant the backup generator wasn't connected. Who knows, so many possibilities.
Virtually every bus will have a feed and one or more cross-ties or back-feeds. A failed contactor is 100% designed for and with possibly the sole exception of RAT-only flight, entirely designed around. Plus, of course, flight on batteries only or PMGs.

No bus is essential on a modern aircraft.

Boeing treats everything electric as a black box but the A380 has this beautifully overkill drawing - given both have 4x generators, 2x APU generators, and a RAT, it should not be entirely dissimilar levels of redundancy:

Note that the reason for some links having two contactors in series (e.g. BTC5/6 or BTC7) is because this is spread across two separate units, so that a fire and total loss of one leaves ~half the aircraft powered and totally flyable.


Okay! Many thanks for that! Of course, it very much complicates the picture, and I'm very puzzled as to how the Fuel Cutoff Switches and Valves operate. Apparently, the TCAM system shuts off an errant engine on the ground at least, but my concern is not with the software but the hardware. It obviously has an Output going into the Fuel Shutoff system. If the TCAM unit loses power, can that output cause the Cutoff process (powered by the engine-dedicated generator) to be activated? I guess that's the $64 billion question, but if MCAS is any example, then: Probably!
As per TDR, built into the FADEC logic.

Power-open power-close is very common in commercial/situations where you don't want to be wasting energy 24/7 and don't have a defined position for the valve/damper in case of power loss. Done a bunch of them in ductwork and electrically operated windows - your car likely has them, for example.

Last edited by Someone Somewhere; 15th Jun 2025 at 05:08 .

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Icarus2001
2025-06-15T05:02:00
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Post: 11902106
I am sure that if there is any reason to suspect that a systems failure may have been a probable cause, or even contributed in any way to the accident, Boeing, GE, the FAA, or the Indian DGAC will promptly advise 787 operators.
The longer the regulators remain silent, the greater the probability that this has been caused by an operational error...
​​​​​​​ indeed, Occam\x92s razor and all that. If there was a serious design flaw, I highly doubt the fleet would still be operational. It has already been 3 days.
No evidence of engine failure

No evidence of RAT deployment from a poor image.

No evidence of electrical failure.

The teams of lawyers in the UK representing 53 grieving families will be working over the weekend to sign up said families to a class action.

​​​​​​​This is going to get messy.
​​​​​​​
CW247
2025-06-15T05:29:00
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Post: 11902115
No evidence of engine failure - Depends how you look at it, the sinking and inability to remain airborne points towards a possibility

No evidence of RAT deployment from a poor image - There absolutely is, you're not following fully I'm afraid. There's a brilliant video by Juan Brown where he compares the sound of the plane passing with that of an American 787 on final with the RAT deployed. Identical sound. The image is not conclusive but I'd wager a bet on it.

No evidence of electrical failure - Except, mention of flashing lights inside cabin moments before by the sole survivor and (sorry old boy) - The RAT ;-)

The teams of lawyers in the UK representing 53 grieving families will be working over the weekend to sign up said families to a class action - Well....

​​​​​​​This is going to get messy. - Agreed
​​​​​​​

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Icarus2001
2025-06-15T05:37:00
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Post: 11902119
No evidence of RAT deployment from a poor image - There absolutely is, you're not following fully I'm afraid. There's a brilliant video by Juan Brown where he compares the sound of the plane passing with that of an American 787 on final with the RAT deployed. Identical sound
Dont be afraid. I am following along. There is no evidence. Can you vouch for the authenticity of the audio recording? I cannot see a RAT in that image only a blur.

I tell you what I am watching closely, the words and subtle meaning in the press conference of Civil Aviation Minister, Shri Ram Mohan Naidu, who has set up a “special high level committee” to oversee the investigation of this “incident.

A little odd given they have the DGCA and AAIB in place, dont you think?

He indicates they are to report within three months.

It is now 48 hours since the EAFR was recovered. A small group of people know the answer NOW.

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Australopithecus
2025-06-15T05:44:00
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Post: 11902125
1. The original video, not the video of a video, has the distinctive audio signature of a deployed RAT.

2 That video shows something dangling down where the RAT is located.

3. There are no typical engine sounds heard.

4. The flaps are extended in that video, and the slats at least are extended in the wreckage pictures.

5. There was no tail strike, so you would conclude that the performance figures were at least close to the actual mass and thrust required.

6. Given the above, and the straight flight path without rudder deflection which ends in a crater instead of Gatwick, you pretty much have all the evidence you need to conclude that there wasn’t sufficient thrust and that what little thrust there may have been was symmetrical.

7. While there are many things common to both engines, the most frightening are a system failure and inappropriate crew action. Oh, and some previously unheralded MX action.

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