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

I have to agree with everything here except your assertion about engine shutdown.
Even though these are big engines with plenty of inertia, when you select engine shut off they spool down very quickly if on load. IE, The generators, two per engine and hydraulic pumps, etc, being driven by the (relatively) small mass of the N2 rotor will drag the speed down very quickly, the gennies will trip offine in seconds, the pumps will quickly reduce flow and pressure.
As for what went wrong.
If the engines have stopped working there has to be a common failure mode, fuel is one but as has been said, no other aircraft has had a problem, as far as we know. FOD? It would have to be something major to shut down two GeNX engines and there would be debris all over the runway, we would know by now.
I have no idea if the RAT has deployed, I can't see it in the video and the noise could be something else.
We shall see.
There is compelling evidence that flaps are set correctly and not retracted inadvertently.
I await further evidence.
Edit to add. LAE 40 years, type rated on 737 to 787 with lots of others in between.

neither of these make much sense to me though as surely the 787 has high alpha as well as low speed envelope protections. reaching either of these states the plane\x92s protections should\x92ve kicked in right? I\x92m still yet to see evidence of a screaming engine in the last moments which would be conducive with the plane applying TOGA when entering a low energy state

the ALT capture is what caught EK\x92s 777 out in DBX right? I still can\x92t think of a logical reason why they continued to allow ALT capture below thrust reduction height (depending on your operator 400-1000 AGL), that seems like a latent threat.

Copy, thanks. The RAT on the Gulfstream GVI/GII does not deploy automatically, but we have other backup systems in addition to the flight control Electrical Hydraulic Backup Actuators. We deploy the RAT on the Production 1 Test Flight, but I have never had reason to use it during normal flight operations.

The solenoid is powered to deploy the RAT. Otherwise it would deploy when parked with no power. Speaking as an engineer from the factory where they are designed, built, and tested.

Still valid Dave. That AD was raised circa post #248 (Search thread for \x93AD\x94)

All four Variable Frequency Generators (2 per engine) going offline at once is too much of a coincidence not to mention that AD.

RAT deployment has been substantiated, which occurs automatically, extension of which takes about 6 secs & would be heard by pax in the cabin as a loud \x93bang\x94 as the leg locks into place.

The sole on-board survivor quote regarding flickering green/white lights (Emergency Exit lights) directly adjacent to his seat 11A, speaks to electrical disruption during the takeoff phase.

If the double engine failure or electrical bus/distribution failure causing loss of thrust occurred for a reason other than the AD mentioned above, the cause will need to be established without delay lest the void is filled with mis-information, fear, uncertainty, & doubt.
The current level of trust in the manufacturer is fragile for good reason.
.
This occurrence will have operators & regulators around the world reviewing their risk assessment models, especially regarding Master Minimum Equipment List (MMEL)/ Defect Deferral Guide (DDG) maintenance relief.

Compliance & maintenance come at a cost.
Lack thereof comes at a far greater & heavier cost.

I attempted a rudimentary timeline analysis of the two most prominent videos. Folks on here are usually far quicker & more adept than me at producing this type of analysis, so approach the following with due scepticism!

Please verify the videos using the links below, so we know we are all talking about the same thing. I deliberately avoid any judgment regarding theories posted thus far - I am merely supplying information against which you can further test those theories.

1. Primary eye witness video with audio:

[ X link ending 1933089931347345596 in case the hyperlink itself doesn't work for any reason]

- Footage starts with aircraft directly overhead, give or take, (based on both sound & vision)
- 13 seconds from start until fireball clearly visible above roofline

2. Airport CCTV:

[X link ending 1933162059556159903 ]

- 49-50 seconds until impact and fireball clearly visible

Subtract the 13 secs noted in video #1 and this establishes the approximate moment the aircraft passes over the video witness's position when viewed from video #2 (CCTV):

49 - 13 = 36 secs into video 2

Estimated timeline (CCTV #2):
19s: rotate
31s: climb rate noticeably deteriorates (12s after TO / 18s from impact)
36s: estimated moment aircraft overflies eyewitness camera (17s after TO / 13s from impact)
38-40s: pitch up then descent begins (19-21s from TO / 9-11s from impact)
49s: first contact with ground (30s after TO / approx impact)
50s: fireball visible above rooftops

Conclusions from combining both videos:
- Aircraft overflies eyewitness camera roughly 13 secs before impact
- This is well after it has stopped climbing (~6 secs)
- This is also mere seconds before CCTV shows the aircraft pitch up and start to descend (which I believe I can substantiate in the eye witness video, although this is tougher to confirm with the naked eye from this viewing angle - someone may have to look more closely than I can this evening!)
- I have previously asked questions about the audio in video #1 and whether we can draw any conclusions regarding RAT deployment & engine thrust. There are strong opinions on both sides. Your personal view on this will influence your evaluation of what the videos show, but either way your theory needs to fit the timeline (or advance a different one).

So, anyone who is developing a theory ought to consider whether it is consistent with the following:-
- rate of climb decays to 0ft/m within 10-12 secs of rotation
- RAT (possibly) audible within 17s of rotation *
- pitch up shortly afterwards with no discernible increase in engine noise & unable to arrest descent
- impact with ground within 30 secs of rotation

* I recognise that the RAT deployment is not an established fact, but any theory that proposes RAT deployment needs to take into account this timeline in addition to the rest.

Alternatively, you are welcome to refute this simplistic, late night analysis of the limited video evidence.

Good job piecing the two together. Flight time ~31s, climb seems to have fizzled out very soon after liftoff. IDK how anyone can listen to the audio on that first video and not conclude that the RAT is out and the engines are quiet. Unless the audio has been altered...

1) The flap retraction would immediately result in progressive less lift, not only after full retraction . The time in the air could have been longer than your estimate, maybe enough time for full retraction

2) if 200 feet in MCP, why would that lead to a descent? Shouldn't that result in level flight?

3) wrong TOW / too low power setting sounds like a plausible event.Happened before. But with full power / TOGA set in the air ( which surely must have happened)I would expect at least a longer struggle rather than the constant descent. Just a gut feeling though, busdriver, no experience on 787. Maybe already in a power on stall. The only problem with this hypothesis is that it does not explain the gear down since there definitely was positive rate after rotation.

4) double engine failure too remote, no signs of flames etc. Forget it, agreed.

My guess remains inadvertant flaps retraction for what it's worth.

A summary of the more certain things we know about the accident so far:

The takeoff run was from the full length and appeared normal, even after comparing with the same flight on previous days. This very much reduces the likelihood of it being a performance issue, e.g. wrong flaps, derate, ZFW/TOW, etc.

Shortly after takeoff, the gear started retracting but stopped in an early intermediate position. At the same time the aircraft climb rate dropped off, then it started a shallow descent. This is consistent with a loss of electrical power causing a loss of hydraulic pressure and total engine thrust from both engines reducing below that generated by one engine at the takeoff setting. The position reporting also went offline at that moment, indicating that it was likely load shed due to an electrical malfunction. What exactly caused the engine/electrical issues remains speculative. An action slip mistaking flaps for gear seems much less likely as due to the above, the correct selection was probably made.

From the videos of the last moments, there is strong evidence that the RAT was deployed, which has a very short list of possible triggers. The sole eye witness from inside describes power issues which lends credence.

Taken together, it seems that there was an event (or events) shortly after rotation that compromised both engines and the electrical system. There is no evidence yet of birdstrikes and continued engine operation *should* not be affected by the aircraft electrical system as they are independently/internally powered, so logic would have the engines failing first leading to a cascade of other problems. Something that affects all engines pretty much simultaneously is a rare beast but it has happened in the past; outside of a deliberate selection of the fuel and/or fire switches for both power plants there is fuel contamination, FOD and not much else. Its seems at least one FDR has been recovered so depending on where they take it for read-out, we should get some initial facts fairly shortly.

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

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?

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.

This indeed is the best summary till now

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.

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!