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

That was included to discount the possibility that it was an autothrottle failure or some kind of mode issue - none of these would cause the engines to go sub-idle/fail, leaving the busses unpowered and triggering the RAT. Only a deliberate action or something affecting both power plants at the same time would cause what appears to have happened, so that seems to be the area where most speculation is required?

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 would say an average passenger has problems differentiating between thrust and G.
Even after engines lost all power G could still vary quite a bit as the pilots tried to crash with as little energy as possible. Any passenger could feel this varying G as varying thrust instead.

How is misselected flap still being discussed? Misselected flap does not cause gear retraction to cease nor cause the RAT to deploy. Both of which are (subjectively) evidenced in the videos. What is the supporting evidence for misselected flap?

Yes absolutely. 100% catastrophic loss of power when getting airborne. No evidence for bird strikes\x85no severe eng damage symptoms in the videos, no mention of birds in the mayday\x85

they\x92ve gone TO power all the way to rotate, no power issues, no eng fuel issues, but as soon as its wheels off they lose all power. That can\x92t be coincidental. TCMA certainly fits this scenario especially with ground/air logic.

As so much of the analysis hinges on whether or not the RAT was deployed, I notice that back in 2015 on another forum somone posed the question
https://forum.dcs.world/topic/119812-787-deployed-ram-air-turbine/"I wonder why so many of these 787's land with their Ram Air Turbine deployed?"

Ttere are a number of videos around showing 787s landing with RAT deployed and it appears that this happens with 787s more than other types.
Can any knowledgeable Pruner answer this? Is there a problem with the 787's RAT and its deployment, or is the deployment a symptom of a problem within the 787s systems?

Regarding the sound believed to be the RAT: Some people suggest that the sound might come from the street, not the plane. I'd say the apparent doppler effect heard would indicate otherwise. It would be interesting to do a spectral analysis to check if the frequency drop is indeed compatible with the expected doppler effect. I wouldn't be surprised if several readers have the software and know-how to perform a simple analysis.

Each Boeing 787 will perform at least one testflight at Boeing before delivery to the customer. This flight has the RAT deployed as a test. Most if not all videos you see were made at Boeing Everett Factory. You will see a couple of times a B787 in the Boeing livery.

What else could it be? A motorbike\x85no. A power drill or other construction noise\x85no. An air conditioning unit\x85no. A cement mixer\x85no. I\x92m struggling to think of anything else you could find in an Indian urban area that sounds almost exactly like a RAT and just happened to be making a sound as an aircraft flew over at low level.

Occam\x92s Razor is in play here.

This indeed is the best summary till now

Hmm. Not sure where the idea comes from the gear was partially retracted... I can't see any signs for it on the video, nor can I see a RAT. and just to say "some event" must have happened is not very helpful, is it? Of course "something" has happened, but the question remains what.

Would it not make more sense to assume there is no RAT if no RAT is visible?

Could it be that we as pilots are in general biased to find a technical reason, although we all know the vast majority of accidents are down to human error?

Post 400\x92, on the assumption VNAV engages, the Flight Control Laws command pitch to maintain speed at VNAV engagement\x85up until Acceleration Altitude. So the aircraft will NOT accelerate like you assert in Fact 3. That is not a \x93fact\x94.

The FMA\x92s will be:

THR REF | LNAV | VNAV SPD

it\x92s easy to explain that a small feature is not shown on a single frame of a low quality video when there are also frames where something can be seen where the RAT should be. It\x92s much harder to explain the RAT-like sound clearly audible though the whole video. My money is on that the RAT was out, but it\x92s not a fact.

Deployed RAT doesn\x92t rule out pilot error, so no bias there.

Jonty; "I can’t see a RAT hanging out." (Sorry Jonty for some reason I can't direct-Quote other people in my reply to posts)


It's difficult to see at the best of times - check this high-res pic of an un-connected Air France 787 with RAT deployed.
The video compression and zoom going on with the accident aircraft footage would likely lose the RAT detail - look at the windows - just a suggestion of them - so until a better video emerges it's impossible to say.

Sometimes I think asking the simple questions is the best approach.

Regardless of flap state, RAT state, etc...

Is there any scenario at all that would give the apparent flight path *other than* a lack of thrust? Personally struggling to see one although as a lowly SLF I'm interested in whether this is overly simplistic - thrust but lack of lift would (presumably) result in the same outcome, but further out. Appreciating that the data we have so far on actual flight path is patchy past a certain point.

The very fact that this was so fast (and therefore relative lack of pilot correction possible or possible to take effect) means that the flight path itself should tell a story?

Then of course, if true, one can speculate to death about *why* a lack of thrust.

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.

Hello all,
I personally think this is a good summary of what we can ascertain at this point from the evidence we have.
I am not a 787 driver by any means but with a fair bit of aviation experience. I would be interested in any thoughts on this suggestion regarding loss of thrust:
If we take it as a reasonable assumption as above that it is almost simultaneous loss of significant thrust, and for the good reasons already discussed, it is pretty unlikely that from what we can see/analyse, that the cause of this would be bird strike (expect to see some signs on video if it's significant enough to cause double engine failure) nor fuel contamination (reasons as above re: likelihood, other ac affected and simultaneous nature). TCMA I don't know enough about but it seems that the sensor redundancy/logic protection is so high it would not be the sole cause.
On this basis, should we perhaps consider the causality of a total electrics failure of some kind first, leading to deployment of the RAT, gear retraction cease etc. Clearly the independent FADEC power generation systems would mean this doesn't on its own prevent thrust control of the engines but could we then be looking at cascading faults (possibly exacerbated by latent faults below the MEL/defect threshold) that contribute to dual power loss and sensor/system issues in throttle response not resulting in FADEC commands to the engines to increase thrust. So even at that point 'firewalling' the throttles could tragically not recover the situation?
Very happy to be corrected by those with much more experience and understanding of big jets operations and systems!

And it seems likely that an "out of the ordinary" noise prompted the guy to start filming

At the airspeed this stricken aircraft was at, was there enough airflow to spin the RAT sufficiently to produce a significant acoustic result?

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.