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

Sometimes complex sequences can have very simple causalities. A lot of complex speculation in this thread so far focused on highly technical things. Yet the basic fundamentals of powered flight have not changed (despite our attempts to do so) over the past 100 years.

1. As a general rule it is a bad idea to run out of either altitude or airspeed or both.
2. If you try to maintain altitude without sufficient thrust you will eventually run out of airspeed.
3. If you have sufficient thrust you can maintain your altitude at a given airspeed, and if you have excess thrust you can maintain your airspeed and increase your altitude. If you have lots of excess thrust you can increase your altitude and increase your airspeed.
4. If you try to increase your altitude by pitching the nose up, and without sufficient excess thrust, your speed will decay quickly, up to the point of stall, at which point you will lose any small amount of altitude you have gained and begin descending.

So…

Fact 1: The airplane stopped going up because it lacked excess thrust necessary to sustain the climb, and;

Fact 2: The airplane’s airspeed decreased constantly because they were trying to maintain either altitude or the climb, but lacked the thrust to do so, and;

Fact 3: If they had prematurely raised the flaps, the climb rate would have decreased/possibly turned negative, but the airplane would have continued to accelerate.

So where did the thrust go?

Fact 4: There is no adverse yaw seen in any of the videos, so wherever it went the loss of thrust occurred (nearly) simultaneously in both engines.

Fact 5: The only way to stop a jet engine from thrusting (sorry) is by either blowing it up or removing the fuel supply. If it blows up- like from birds trying to become a fuel source, there will be evidence. (See Jeju Air for a good example.)

Fact 6: There is (so far) no evidence of either engine blowing up. (I’m deliberately using highly technical terms here…)

Fact 7: There is unmistakably clear audible evidence of the RAT being deployed on the raw video from the right rear quarter of the airplane. Near supersonic propellor blades are an unmistakable sound- the RAT was definitively deployed no matter how much people want to argue to the contrary.

Fact 8: In the same video there is silence from the engines when they should be thundering at full (or nearly full) power. (Yes, I know that isn’t a thing- I am a simple man alas.)

Thus the only possible conclusions are (cringes as he waits for fdr to rip him a new ah):

1. The engines stopped burning, at nearly the same moment in time.
2. As a result, the airplane stopped climbing and also began to lose airspeed in an attempt to maintain altitude.
3. The RAT being deployed so quickly means that the ‘puters believed both engines were dead donks. (They were.)
4. If both engines ceased burning it meant the fuel supply was interrupted. We aren’t talking flight idle here- it was lights out for both.
5. (I am quoting someone else here) There is enough suction for the fuel to feed even if the fuel pumps are inop.
6. The engines stopped being provided with fuel. Because something physical was placed between the tanks and the burners. And they flamed out.

The $64,000 question here (remember when that was a lot of money??!!) is simply: What stopped both engines from getting fuel?

There are a very finite number of possibilities to that answer- and I do have my suspicions, but I lack the qualification to opine on that one.

I’ll leave the rest to the more experienced folk here.

Warm regards-

dce

I hesitate to chip in in these accident threads. Keep them clean. However, as as a few comments above brushes my audio expertise, I will comment.

A very simple audio analysis give me this:
The 3 segments horisontally, are of different videos of B787s passing overhead/landing. The vertical drop you see is the doppler effect.
In other words, these are spectrograms over time which makes these distinctions easier than a simple static spectrogram.
1. B787 landing with RAT extended.
2.Air india crash
3. B787 landing without RAT


It's a 5 minute laptop job, and it would look much prettier and clearer if I spent some time with it, (Gain to color match, and spectrally match to compensate for microphone placement and type),
but it is 85% conclusive even when done as simple as this IMO.
(I do have legal forensic audio experience)
The RAT was out judging from the audio evidence. You can see the the equally spaced overtones of the propelller match when passing overhead resulting in the Doppler effect, the difference in length of the doppler is caused by distance and the slightly varying frequencies shown in the starting point is caused by a difference in speed. But the harmonic content match.
In the 3rd segment you see none of these overtones at all.

I hesitate to chip in in these accident threads. Keep them clean. However, as as a few comments above brushes my audio expertise, I will comment.

A very simple audio analysis give me this:
The 3 segments horisontally, are of different videos of B787s passing overhead/landing. The vertical drop you see is the doppler effect.
In other words, these are spectrograms over time which makes these distinctions easier than a simple static spectrogram.
1. B787 landing with RAT extended.
2.Air india crash
3. B787 landing without RAT


It's a 5 minute laptop job, and it would look much prettier and clearer if I spent some time with it, (Gain to color match, and spectrally match to compensate for microphone placement and type),
but it is 85% conclusive even when done as simple as this IMO.
(I do have legal forensic audio experience)
The RAT was out judging from the audio evidence. You can see the the equally spaced overtones of the propelller match when passing overhead resulting in the Doppler effect, the difference in length of the doppler is caused by distance and the slightly varying frequencies shown in the starting point is caused by a difference in speed. But the harmonic content match.
In the 3rd segment you see none of these overtones at all.

There has been much discussion here about RAT deployment. Various claims either way have been made, based on individual perspectives of available video and audio.

I am very mindful of just how awful a tragedy this is, and have significant misgivings about disproportionate interest in others misfortune where it carries no purpose, but also recognise that for some people knowing and learning what happened ASAP could be very important, particularly given the present circumstances.

Thus while I sincerely hope that early detail from investigators will give some clarity, in an effort to reduce needless speculation regarding RAT deployment I have taken:

(1) an audio sample from the video of AI171 passing by in which people claim to hear a RAT
(2) an audio sample from a 787 video with RAT deployed on test by Boeing
(3) an audio sample from a JAL 787 video with RAT deployed

And passed these through a FFT in order to gain a more quantitative view of the noise spectra from each event.

A spectrogram of the results is presented below. I hesitate to make any conclusions per se, but observe that there are similarities as well as divergences between them. In all three samples there is a relatively consistent signal roughly centered in the range 113-146Hz that could be what gives the characteristic 'buzz' sound of (apparently) a RAT in operation.

JAL ~141Hz
Test ~146Hz
AI171 ~113-134Hz (prob doppler variation here)


Spectral comparison AI171, B787 with RAT, JAL 787 with RAT



Spectral comparison #2 AI171, B787 with RAT, JAL 787 with RAT


These frequencies seem consistent(ish) with what I got from this video [[url]https://www.youtube.com/watch?v=O1r3CuRwjPc] in which a 787 RAT is being tested - albeit in this case the blades are hydraulically powered and not driven as a turbine. This test showed a fundamental frequency of 135Hz with relevant harmonics above (the second harmonic at 270Hz is higher SPL, no weighting):




It's important to note that the initial recordings are necessarily different; these are not controlled conditions, the recording equipment is probably quite diverse and almost certainly not ideal, and the environmental conditions will also be different. Moreover all of these audio samples have come from video files referenced here, one has no way of determining the provenance or veracity of these sources and, crucially, I have no prior experience of analysing/extracting RAT acoustic fingerprints (nor have I sampled 'control' audio of a 787 passing by /without/ RAT!).

Additionally it's been quite a long time since I did any work with [turbine] noise so given these and other variables I'm not prepared to make any declarations per se, but perhaps more knowledgeable people could. That said, my feeling from what I see is that RAT deployment is not dis proven, and that the apparent fundamental frequency difference between the samples may be explainable by - amongst other things - difference in a/c airspeed, bearing in mind that AI171 was on TO, the others were landing.

Ultimately what I've done here is extremely rudimentary and while it would be possible to go into much more depth I'd hope that more definitive answer would be forthcoming by then, however if anyone wants to discuss specific methodology etc off-line please PM, no wish to add to noise on this thread.

FP.

It was hard to let it go, so I spent a bit more time with the audio, using filtering and matching to see if I could be even more sure.

It's a pity uploading audio to this site isn't as easy as uploading photos, but I can say it took very little filtering and matching to make the Air India audio become nearly indistinguishable from audio taken of B787 with known RAT extended during landing.

I can't see it in the photos either, but in these circumstances the audio is a lot more trustworthy, and from my audio point of view RAT deployment is 100% confirmed.

In the off chance that the audio I borrowed from a confirmed RAT event was somehow faked, I plotted the technical data I could find of the B787 RAT (4000rpm, 2 blades) combined with a height estimate and asked the O3 model with deep research to estimate doppler shift and speed.
The result matches the above documented 270-200Hz (in one of the harmonics) Doppler shift observed in 1.7 seconds.

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.

I have seen your previous posts about this, and I happen to agree. Visually, as a lay man non visuals expert, I am in your \xabcamp.\xbb

However, the rat is small, and the artifacts are plentiful. Small sensor, compressed video, compressed upload, zoom, it is in short an awful source.

However, the RAT is a much better noisemaker, and the audio signature is much more obvious than it’s visual appearance in this case, and though the recording isn’t fantastic quality, there was more than enough information there to objectively conclude the RAT is out. And that is my professional, on the weekend, opinion.

I want to ask a pretty frank question for all of you, and I hope it is ok, from an audio specialist non-pilot:
Provided the engines spooled down. Provided the RAT is out. (There are no explosions, no bird strikes.)
Isn’t software and previous electrical failures a red herring too?Would anything but a complete fuel shut off lead to this result? That still leaves everything from the Fate is the Hunter plot, to Airbus A350 center consoles and Alaska 2059 open as root causes.

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.

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.

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.

Correct. That was the original purpose of the calculation. In addition to the sound itself having the measurable harmonic signature from other rat videos.
What this plot also does however is tell you the speed if you know the height or height if you know the speed.

The iphone used to film this were pictured somewhere, knowing the iphone model, and thus the characteristics of the camera, and the dimensions of the airplane it wouldn't be impossible to calculate height from the video imo.

Just throwing it out there if anyone sees the use and feels the call.

My personal amateur speculation still centers around the cut off switches.
I have spilled coffee and sweet tea over complex electro/mechanical switches/panels before(large format audio consoles with 8000 buttons) and seen unexpected things happen.

I am sure the switches are spectacularly well built, but they are in close proximity and thus prone to the same external factors.
Does anyone know if these two cut-off switches in such close proximity has the exact same installation, or they differentiated in some way that makes a freak failure mode in one not neccesarily affect the other the same way?

I realise the discussion has largely moved on, but for completeness I have analysed, filtered and compared the audio from several 787 videos\x97both take-off and landing (the latter with and without RAT deployment; take-off footage with the RAT out is rare).

Using the same style of frequency plots employed in the RAT analysis\x97and drawing on speed of different engine components data supplied by other contributors\x97it is straightforward to identify the engines\x92 high-power acoustic signatures objectively, despite variations among clips and the presence of Doppler shift.

What is clear is that the engine noise in the recording bears no resemblance to a typical 787 take-off profile. Whether the engines were merely at very low thrust/idle or fully windmilling I cannot say with certainty, but they were certainly nowhere near take-off power.

Make of that what you will.

The audio analysis in this case isn't anything obscure or vague. The same software is used in courts all over the world every day. You can be pretty sure the same software in some iteration is used investigating CVRs all the time. It shows something emitting the exact same sonic signature as a B787 RAT went over the camera at the same speed as the Boeing 787 seen going over the camera. It isn't a broken fanblade, or a motorcycle passing by, that would give a completely different result. It literally means hundreds of thousands of datapoints fall into the exact same pattern. If it were anything else, that would be easy to observe. It is a much more accurate tool than watching heavily compressed video. It is the same software used in hollywood to surgically remove airplane noises from historical dramas, btw. At least until AI came along and took on that job about 2 years ago. . Just because you aren't familiar with it doesn't mean it isn't accurate.
Just putting this out there, since many might be unfamiliar with this, you included.

As one of the two authors who have offered an acoustic analysis of the AI 171 'RAT' video here I feel obliged to make some observations.

First of all Kraftstoffvondesibel and I did our work completely without knowledge of each other. We reached the same conclusions more or less, most likely using different software (I used four different methodologies) and in subsequent discussions between us we've found our specific results (frequency etc) match very closely - including the doppler shift that we've also both commented on.

While this doesn't absolutely prove the RAT scenario (I was, at least initially, somewhat more circumspect on this matter as anyone reading my first post would find) it does go some distance towards reconciling our respective methodologies and outcomes. Given the confluence and discussion I am now more satisfied that the RAT was deployed than I was before - although for the reasons espoused earlier I totally recognise the [scientific] challenges to this view.

In this regard I too would not 'mind' if our view regarding RAT deployment were proven incorrect. What Kraftstoffvondesibel and I have done is simply use a little science and apply a quantitative analysis to the available data that many had qualitatively argued over. One might hope that, amongst other things, it could have dispelled the RAT/no RAT question to some degree and reduce thread noise, but unfortunately it seems some haven't read the thread through, or perhaps lack analytical reasoning.

This site isn't the place for a full academic paper+peer review and for me the real subject of this thread is the tragedy of AI 171 and what might determinable from what we know in the hope it will be useful to those closer to the coal face. If you are a physicist, scientist or engineer and have the capability then the same data we used is also available to you to do your own analysis. Should you do so we'd welcome hearing the outcome - whether it concurs with our results or not - as this is the scientific way. If you want to include the full nitty-gritty detail of how you've gone about then for a very small percentage of us that might be interesting, but it'd be peripheral to the main issue - and bear in mind that RAT deployment itself is merely an indicator of other potentially more serious issues. It is not likely to be the cause per se !

To conclude, I understand it's a long thread but as far as the RAT question is concerned, I'd encourage you to read the relevant posts at least and if you remain unconvinced, and you have the skills, then why not conduct your own analysis and let us know the results? Otherwise perhaps as a group we could move on from this, remembering that this is a terrible event which at the very least deserves informed useful discussion rather than wild and/or repetitive speculation.

FP.

I don't believe I owe you anything, I believe this is done adequately previously and has already taken up enough time on this thread. I am of the opinion that we have shown the RAT being deployed satisfactory enough to be of use for speculation in this thread. I find repeated comments about the bad video being the only evidence a bit disrespectful, though. Even from a mere physicist. It is based on a spectrogram over time. The source file shows audio up to about 16 kHz, it is unknown whether this limitation is in the file format (ie. 32kHz sampling rate) or microphone. Doesn't matter much. The frequencies above 16kHz is not important in this context as it is not where the sound energy is anyway. The audio will have been lossy data compressed, but it does not affect these prominent properties of the audio. It does make me hesitant to draw conclusions from the parts of the spectrum with more broadband noise and several intersecting sounds. Noise floor suggests 16 bit sampling depth. Spectral resolution? N/A All samples are included. The spectrogram covers the entire frequency range recorded, It shows comparatively the same overtones of the fundamental expected from the technical specifications of the 2 bladed RAT running at it's intended RPM, the doppler characteristics fits completely with a reasonable range of passing speeds and distance to the passing source plotted out. Compareatively, All the harmonics are identical both in pitch and seperation to a recording of a known B787 landing with RAT deployed, while the Doppler fall shows a longer time frame in the landing video taken from a further distance. As expected. The overtones easily discernable in this recording falls in the 220-2700Hz range. Below that, there is other noise centered around 150Hz, which gradually fades towards the end of the recording. This, as far as I can find in available information, fits with an idling or even windmilling B787 engine, but this is not conclusive. This falls in a range of the spectrum where there are other noise sources and the signal/noise is low and of a broader band characteristic, these masking frequencies is where the lossy data compression might play tricks, so I do not weigh that heavily. Recordings of landing B787 without the RAT, shows none off the same characteristics, and completely lack the tonal components and exact overtones shown with the RAT deployed. More importantly, compared to videos of B787s taking off with normal take off thrust, the latter shows distinct tonal elements, but with very different overtones,, both in separation and composition, again possible to relate to known quantities of the rotational speed and elements of the engine at high power. The AI recording shows none of this.

The latest techniques let us separate such things as reverbration from the source, when superimposing the reverberation/ambience and background noise of the AI crash urban environment on the clean, dead open field recording of the known B787 w/rat, they do indeed sound exactly the same to this very skilled and experienced listener. Although this is not courtesy of the computer analysis. It is just another angle of confirmation.

All in all, i think this source audio is excellent. The source is an iphone, their mems based microphones, although noisy shows great spectral balance and is comparable to basic measurement microphones of professional application. There is plenty of information to analyse from in this sample.

And again, I can't see it in the video either, and until I put on some really expensive headphones and fired up the software I was of a different opinion. I bowed to the science.

Edit: I took an extra look, I am prepared to say the fall off at slightly above 16kHz is from the original recording, this is probably a limitation in the microphone, as it is not a hard cut-off before a 16kHz Nyquist frequency as it would be with a 32kHz sampling rate, there is dither noise from 16-20kHz fitting with the source being 16 bit.

As is often the case "confirmation bias" is probably why he keeps trying to do the "reversion to authority" thing.
He has some other theory, and nothing to back it up, so continues to claim he can't see the obvious pattern in the data.
It's irrelevant, because there's really NO evidence to the contrary.
And by now, there's now FOUR solid pieces of evidence that the RAT deployed, so your analysis appears to be correct.
This includes the other "ballistic" analysis of the ascension, and subsequent descent, curve-- which indicates an approximately 100% loss of thrust from both engines.
In such a scenario, the RAT automatically deploys. Audio, visual, witness and classical physics all support the conclusion that, more likely than not, the RAT deployed.

The larger mystery, obviously, is the sight line through the swiss cheese that caused the chain of events resulting of Loss Of Thrust. We should hear the Preliminary within a month or so.

Every airline training course I have had stressed never touching a critical item below 400 feet. That was later changed to 1000 feet at my airline. . I can\x92t conceive of the crew shutting a engine down in the first 8 seconds of flight.

I agree with your analysis about RAT. The source is usable, although far from the original quality.

The cut-off at 16 kHz is typically caused by lossy audio compressions (AAC), not the microphone. In this case, the audio was compressed two times (first the iPhone, then the Twitter). A microphone does not simply cut all frequencies above the certain point.

Also, this audio content is Mono (the same signal on both channels) - an additional loss of information, if the original recording was Stereo.

I've ground tested countless RAT's on 757/767's over many years....

Having just watched (or more importantly listened to) the latest video by Captain Steeeve on YT, I'm fully confident the deployed RAT can be heard

Not trying to be a smart ass, but how do you "ground test" a RAT?