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

No, it would have looked very different in the analysis.

About the engine spool down not present in the audio:
I did not know engines spooled down that quickly if shut down in the air, I am not an aerodynamicist, but it makes sense it would happen with all the drag. I had a mental sound in my head from normal shutdowns, and action movies I guess.
That means my point about it being no spool down detectable in the audio really doesn\x92t matter.

Is there known numbers for timing RAT deployment or spool up? Because there is no sign of that either in the audio.

I will have a go at a few after take-off videos and use some alternative comparison techniques to see if I can say anything with certainty about any engine power being present or not.

My hunch, after analyzing a few landing videos with and without the RAT with the standard audio analyzers tells me the engines were at similar or below rpm/noise making level/thrust compared to a normal landing, and that they had already completely spooled down(which you guys suggest is to be expected to happen much more quickly than I thought, so maybe doesn\x92t say much) when the video with audio starts.

Given the quality of the video you cannot see that the RAT is NOT deployed either

Fair point Pip.

I just saw a picture of the tail (taken from above) and the APU door is partially open?

I believe the 787 has a similar APU automatic start function with loss of AC power just like the 777. It looks like the APU door was starting to open to allow for an auto start.. Similar situation to that BA 777 that landed short in LHR due to fuel icing.

Its looking more and more like an AC power loss.

Interestingly, the DGAC order for AI maintenance to check those random 787 systems are all associated in some way to an automatic RAT deployment.

Thank you for commenting on the DGAC order. I'm just a lowly SLF, but it struck me that the DGAC seemed to be focusing initially on fuel and power issues. I've been surprised there's been so little comment.

A slight decrease in two engines is still far better than a loss of one engine, and that has to be manageable.

787 has four main AC buses. Cannot find information on the standby/emergency buses but I would probably expect two.

There's a list of equipment operable on battery/RAT here, but I'm not sure which (if any) is the transponder (26:10):
I think the post you replied to was in the context of mandating APU on for takeoff. Could just say "on if available", though.

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.

If you had gear pins and an engine loss, I could maybe see climb rate being zero or slightly negative. Not the brick impression we see here.

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.

Considering everything that's possibly to be found in the vicinity of the plane in the picture, I don't think we can conclusively say that's the RAT deployed.

There are a few comments along the lines of "it is incredibly unlikely that..." this is selection bias in reverse. Something incredibly unlikely has happened, and it's contained in this sample set.

To summarise some known facts about the TCMA system:

1) TCMA will shut down an engine if:

• It believes via multiple redundant sensors indicate the aircraft is on the ground
• It detects engine power in excess of that set by the thrust levers - subject to a margin to account for engine performance variation - that is determined to be a runaway condition

2) In 2019 an ANA pilot was able to confuse the TCMA by rapidly moving the thrust levers into reverse, to forward and back into reverse again. This caused both engines to shutdown.

3) Since then the TCMA should have been updated/fixed (and indeed the software will have been updated by SB since the a/c was delivered, to detect a wider range of runaway conditions)

And speculation:

4) It may be possible - given the close timings - that a TCMA activation occurred as the a/c was leaving the ground, with kinetic energy and spool down time getting the a/c from the ground to its peak height

In the recent BA LGW incident the PF reduced thrust to idle at V1, then added thrust back, then committed to a RTO. I wonder if something similar could have occurred:

• In error, PF reduces power to idle at a speed approaching V1
• Engines begin reducing power, but n1 reduces more slowly than the TCMA system is expecting (perhaps because the TCMA margin is calculated when the a/c is stationary, but at 170kt a turbofan will spool down more slowly due to the ram air / windmill effect)
• TCMA detects a runaway condition - while a/c is on the ground - and cuts off fuel via the relay circuit
• PF decides to commit to takeoff and rotates, not knowing that TCMA has already activated
• 10-15s after rotation, n1 has now dropped below minimums for electrical generation. Electrics fail, final transponder signal is sent, and RAT is deployed

Obviously this should not be possible, and there are other possibilities.

Extremely likely the RAT was out:

1. there are multiple frames of the video showing ' something' at the position where the RAT is located under the fuselage
2. the sound in the video which is very similar to a deployed RAT
3. the sound analysis posted here by multiple people
last but not least
4. the aircraft stopped transmitting ADSB data shortly after the rotating. This indicates an electrical failure. Other aircraft ADSB data was picked up by FR24 receivers indication there is a good reception of the signal in that area.

Agree with most of your comments, but Lauda 004, the B763ER/PW4060 aircraft, no evidence was developed to indicate a G/A sensing fault. The report is available on line,

Lauda Air B767 Accident Report

Lauda 004 taught that the flight test of reverse had some assumptions that were not accurate. The reduction in lift from the flow interaction with the wing was not recognised before Lauda 004, and before that was discovered, there were a lot of flight departments that were rather judgemental of the event due to their own ignorance. Just because our sims say it is so doesn't mean that the aircraft agrees.

This to me makes more sense; perhaps I`ve got it wrong but in the video the trailing edge flaps definitely look up. Maybe there`s more and they weren`t.

On a flap 5 takeoff the FMS could be programmed to select climb power at flaps 1 which would seem like an apparent loss of thrust. Same as for F15 to F5 or further.

I`m not sure if they would have cycled the FCS switches or not. But the airplane certainly would have experienced a loss of lift would the flaps been inadvertently retracted. As well as perceived loss of thrust.

OTOH any castastophic failure which left the gear down would have essentially left the flaps where they were. They are hydraulically activated with electrical backup but it`s wayyyyy slow.

Another hour spent sifting through the stuff since last night (my sympathies to the mods ). A few more comments:

"Real time engine monitoring" is typically not 'real time' - it's recorded and sent in periodic bursts. Very unlikely anything was sent from the event aircraft on this flight.

Commanded engine cutoff - the aisle stand fuel switch sends electrical signals to the spar valve and the "High Pressure Shutoff Valve" (HPSOV) in the Fuel Metering Unit, commanding them to open/close using aircraft power. The HPSOV is solenoid controlled, and near instantaneous. The solenoid is of a 'locking' type that needs to be powered both ways (for obvious reasons, you wouldn't want a loss of electrical power to shut down the engine). The fire handle does the same thing, via different electrical paths (i.e. separate wiring).

As I've noted previously, a complete loss of aircraft electrical power would not cause the engines to flameout (or even lose meaningful thrust) during takeoff. In the takeoff altitude envelope, 'suction feed' (I think Airbus calls it 'gravity feed') is more than sufficient to supply the engine driven fuel pumps. It's only when you get up to ~20k ft. that suction feed can become an issue - and this event happened near sea level.

Not matter what's happening on the aircraft side - pushing the thrust levers to the forward stop will give you (at least) rated takeoff power since the only thing required from the aircraft is fuel and thrust lever position (and the thrust lever position resolver is powered by the FADEC).

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) - and there would be a lot embarrassing questions for all involved. But I personally know many of the people who created, validated, and certified the GEnx-1B TCMA logic - and can't imagine what they would be going through if they missed something (coincidentally, one of them was at my birthday party last weekend and inevitably we ended up talking about what we used to do at Boeing (he's also retired)). Worse, similar TCMA logic is on the GEnx-2B (747-8) - which I was personally responsible for certifying - as well as the GE90-115B and the 737 MAX Leap engine - the consequences of that logic causing this accident would be massive.

The point you think you are making here has recurred throughout the thread. To try and put it to rest:

The first omission/error here is in describing a definite article (i.e. the video), alongside claiming that the pic you posted is 'unprocessed". It might not be processed, it just isn't very good quality. Which you might not realise if you haven't seen the original, higher resolution version of the clip.

The are now numerous social media sources for copies of the flyby/crash smartphone video. Many of them are actually a repost (or possibly multiple independently made iterations) of a second generation recording - made via a smartphone filming the original video playing on a monitor and via the monitor's (likely very poor) speakers. This version has been incorrectly assumed to be (and described as derived from) "CCTV" in some posts. The "screen recorded" nature of this particular version of the video is obvious from the camera movement (including showing the bezel and edge of the screen it is filming), moire patterns etc. The original (or rather, what *appears* to be a first generation, but compressed, copy of the original) version of the video has *also* been posted on social media (and thereafter, here) with both then being dissemanated across multiple social media accounts and at varying video resolution and compression ratios.

There are further posts of the "screen recorded" copy of the video in which AI enhancement and other filters have been used to try and "improve" the video quality. Anyone even attempting to filter the video in that way doesn't understand the way such filters operate (i.e. they are trying to make the picture "more watchable" rather than sharpen it/make it more *accurate*), and anyone trying to draw conclusions from such "enhanced" versions needs to think carefully about what they are looking at.

The framegrab you have posted above is clearly from the "screen recorded" video. The original version (with its attendant much higher video *and* audio quality) *does* appear to show an object beneath the airframe where the RAT hub would be - and also - albeit only for a handful of frames - appears to show the motion blurred impeller disc. The fact that this artifact is only visible for a few frames is explicable via the heavily compressed digital video but it is consistent.

The "full" video itself is also longer than the "screen recorded" version and starts earlier in the incident timeline. And a distinctive propeller-type beat *is* audible, both before *and* after the aircraft comes into frame, at near identical pitch to the various examples we've seen of a 787 passing a camera with the turbine deployed. One would imagine that the first generation copy of the video as it exists on the device that recorded it is noticeably better quality than *any* of the downsampled/overcompressed social media versions we have seen. And one also sincerely hopes that the Indian AAIB are already in possession of it.

The prevalence of smartphones and social media means this sort of footage is more immediately accessible and more easily dissemanated than at any time in the past. However, anyone trying to draw solid conclusions from a clip posted on social media - especiallly with limited quality, and even more, "enhancement", needs to remember the limitations of what they're seeing.

(Not a pilot, but a former aero electronics engineer with significant subsequent digital forensic experience)

Agreed. Also, given an almost 100% likelihood that the RAT deployed pretty early on and the ramifications of this, flaps and gear have almost lost relevance as they wouldn\x92t be able to be moved much after that point during the brief airborne period, even if commanded?

That\x92s not a false conclusion if in fact hydraulics were lost. I dont think that was the case and if it was engine driven hydraulic pumps have normal output all the way down to idle and actually further. I dont think the RAT deployed for any reason and i am not sure that has been confirmed.

A TCMA bug just doesn't bear thinking about, I really hope that doesn't turn out to be the case.

Not to mention the fact the flaps were selected when you view pictures from the accident site. Dare I mention the RAT being deployed too? That does not happed if you select flaps up at the wrong time.

Read the thread about the audio analysis. Its pretty conclusive. The RAT was almost certainly deployed. Plane crash near Ahmedabad..

Like many (most?) here, I really don't have a theory/guess that I would call 'high confidence'. Among those who do, many of them seem to rely in part on RAT deployment. I can't say whether it was or not. I do not believe any of the available pictures and video confidently attest to the situation from a visual standpoint. Regarding 'RAT clearly audible' I would say that we do not know that either. That audio is taken from camera phone video. It seems entirely possible to me that the sound in question could very well be a scooter, or some other ground vehicle that is much closer to the camera than the plane is. So anyone who is confident of RAT deployment has to be equally confident that the sound we hear (I agree there is a sound) could not possibly be anything other than a RAT. That seems a bit of a heavy lift to me. Any number of audio sources not visually captured on the video could have produced that sound. I am certainly not intimately acquainted with the sound of every tuktuk, scooter, piece of construction equipment, etc. that are common on the ground in Ahmadabad. We'll know soon enough but the evidence we have only weakly suggests a deployed RAT.

Thank you for your qualified input! I had asked a question about the ability of the engines to suction fuel if the fuel pumps were inop. Specifically, I wanted to know whether that is ever tested and if so how often and by who. IOW, if due to wear, a maintenance mistake or whatever, if the engines were in fact NOT able to suction fuel, since the SOP is to run all of the pumps would that problem ever be noticed in normal operations? If not, then if both engines had that problem (imagine a faulty maintenance procedure that somehow caused this to happen to a lot of engines) then a sudden, complete collapse of the electrical system would cause the pumps to stop--and thus the engines. If any of that is even a possiblity then all of the other AI 787s should be checked.

I\x92d like to give you another option to consider in what must be a worrying time;
Am I right in saying, from a mathmatical perspective, that dual engine flame out due biocide overdose would be more likely than a TCMA activation shutting down the engines? Considering we have examples of engines reducing to idle within seconds of each other in the past, but we have no examples of airborne TCMA issues I would have thought this to be the case. Likewise, nefarious intent also appears more likely statistically than a TCMA issue.
I have high-school level statistics under my belt so I pose that as a question for people much smarter than myself.