Posts about: "INLINE_IMAGES" [Posts: 229 Page: 5 of 12]¶

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.

While I get your light intent there is a reasonable question there, and one which was posited many posts ago.

There are various reasons why the signatures we obtained are not that likely to be from a motorbike, but to answer briefly - and pictures being 1000 words 'n all that - here's a quick comparative [visual] analysis. At the top is a motorbike passing by away from the observer, the other is AI 171 doing the same thing:




I expect the difference will be clear. That said one could level a number of criticisms at the method I've used to show this, the sources obtained etc (eg. this is motorbike, not a moped as I couldn't find one in the time available), and if you really wanted to fake it one could, but I doubt that's occurred here.

Would say more but I'm short of time and think this is sufficient clear for now.

FP.

This gives us an insight of what, on Saturday morning, the Indian CAA were focused on - and many of them focus on fuel delivery.

The previous 787 groundings were battery related fires. That was solved by a temporary fix. Is that still in place?

I preface this post by acknowledging all the previous posts in this, and the now-closed thread, about the TCMA, in particular the excellent posts by tdracer. (Ditto the noise analyses by Kraftstoffvondesibel and First Principal.)

I also note that the primary source of the information on which I’m basing my post is the content of Boeing’s patent application which, of course, does not contain any of the actual wiring diagrams or modification details of the TCMA, even assuming it has been implemented. (I understand from the now-closed thread, that there is an unresolved question as to whether a petition for an exemption from the TCMA requirement had been successful.)

The point of my post is to get other’s thoughts on one of the design principles of the TCMA system proposed in the patent application.

The ostensibly simple and elegant concept is described in the schematic of the system at figure 1 of the patent application. A copy of figure 1 is below.

The TCMA is the part of the schematic inside the dotted box numbered 16 , sitting with the EEC (others would call it the FADEC) in the solid box numbered 18 .

The heart of the TCMA comprises two switch relays, numbered 22 and 28 in the schematic, wired in series. Each of those switch relays is controlled by its own, dedicated engine control malfunction software, identified as the blobs numbered 130 . (The patent application identifies component 34 as a dedicated processor and 32 as the diode connected to the switch relays, but that is evidently a mistake. Component 34 is the diode and I can’t find a component number 32 anywhere in the schematics.)

Each relay switch and its controlling software is described as a ‘channel’, one A and one B. Both channels run continuously, monitoring throttle position (36 in the schematic) versus engine data fed from ARINC data bus lines (46 in the schematic) and “dedicated input sensors” not shown in the schematic. Those sensors presumably detect things like weight on wheels and perhaps RADALT.

This design is said to achieve redundancy, because if only one ‘channel’ detects the engine is producing excessive thrust while the throttle is set to idle, that channel will set its switch relay to CUTOFF and that is enough to change the state of the high pressure fuel shut off valve (58 in the schematic). No more motion lotion. In the words of the patent application: Both channels are “always actively monitoring engine function and independently have the capability of shutting down the engine.”

That arrangement wrinkled my crusty old avtech brow. In my mind – and this is why I’m seeking other’s thoughts – the advantage of redundancy arising from the two channels, either or both of which can shut the engine down, is not without risk. If it is possible for one of the channels to have some ‘glitch’ or hardware failure such that it does not detect an actual out of envelope condition justifying immediate shut down, with the other channel detecting the condition and shutting the engine down, it inexorably follows – does it not – that it is possible for one (or both) of the channels to have a ‘glitch’ or hardware failure that results in a shut down when there is no out of envelope condition?

Further, even if there are completely separate, duplicated sensors telling each channel things like the position of the throttle and whether or not there is weight on wheels, there remains the possibility of a combination of sensor failures/disconnects resulting in one channel being ‘convinced’ that an out of envelope condition exists, with a consequential cutoff of fuel to the engine.

I of course acknowledge the valid observations made about the remote probabilities of these kinds of glitches and failures.

I’ve heard rumours that there was much resistance to the mandating of TCMA systems. Having seen many, many strange faults caused by random shorts, open circuits, liquid ingress and other foreign objects, I can understand why there was that resistance. Every time you add something to a system and that added thing has electronic components and software and electrical connections and data inputs, you add risk of that thing malfunctioning or working perfectly but with erroneous inputs. In this case, there are effectively two added new things: two channels, each one of which has the ability to shut off the motion lotion to the engine to which they are strapped.

I make no comment on whether TCMA systems, if fitted, have anything to do with this tragedy.

My profound condolences to the families and friends of those killed or injured. My thoughts also go out to the many people who will be agonising over the potential causes and responsibility for it. And thanks to those who are working out the causes.

...

Yes, but it is only designed to retract them in to the Flap 5 position which is the first stage of TE flaps. BTW you will note from the image that F5 is a barely perceptible, hence this likely flap red herring.

Thanks as always TDR for your excellent professional input. It is therefore so much more perplexing that even you cant logic our way out of this impasse. That is, the assumption that the aircraft experienced a double engine failure (supported by a reasonably convincing argument that the RAT deployed), and yet no plausible reason (that we can see) for such an event. So some then collectively slip into the tired and lazy theories of intentional or unintentional crew actions that 1. beggar belief (intentional), 2. defy physics (flaps instead of gear despite clear evidence to the contrary) and call into question the professionalism of a very experienced Captain and crew as well as the aircraft manufacturer (because...well its Boeing so it must be software ).

Yet, the answer must be simpler and staring us in the face since logic and experience (everything you have offered TDR), tell us that modern airliner engines generally do not just suddenly quit flying at the same time. In this regard we can recall several instances of double engine failure associated with bird strikes generally involving large birds or large flocks or both. But it seems we have discounted this theory very early in discussion. Why? Because we cant see any birds, or flocks of birds or engine flames/surges or puffs of smokes from the engines which would support this. Really?

I have read all the 100's of posts (sadly) and while some very early posters tried to analyze the imagery, I suspect the very poor quality eventually discouraged most from seeing anything of interest. However, smattered throughout this discussion from the beginning to the end there have about four posts that describe seeing something where others have not. At least two of these were related to possible smoke but which were probably just the dust blown outwards by the wingtip vortices. Two others however have mentioned possible flames and puffs of smoke.

The video of course is very poor. There should be a special place in hell for people who subject us to looking at a video with continuous zooming in and out, inability to retain focus on the subject (it was just a CCTV monitor, not the actual aircraft they had to focus on) and constant camera shake. A video of a video, and then the resolution probably reduced for social media upload. This all results in a very unwatchable record of the aircrafts departure. The only immediate information gleaned seems to be some idea of how far down the runway the aircraft was at takeoff and the parabolic curve as it very clearly described the aircrafts flight path.




Air India Flight 171 on departure
But take a look at this frame. The right engine shows an artifact (pixelation if you like) that might represent a surge flame. I can almost see a puff of smoke just inboard of the aileron that may be associated with that too.

Am I just seeing distortion? Am I just seeing some smoke because that's where I would expect to see it?
We are all very used to seeing everything in 4K today but back in the day when everything was low res we used to join the dots. If pixels existed then something was there. If they didn't, it wasn't.
So if it's just pixels caused by distortion then they have coincidentally appeared in the tailpipe of an aircraft that crashed shortly after takeoff with a presumed double engine failure.

But surely we would see the birds? Well, not in this video. You cant even see the registration number on the side of the aircraft and that is much bigger than a bird. Haze, distortion, focus and low res, and each individual bird wouldn't even make up a pixel.

So make of this what you will, but this problem may have started on the ground. Birds strikes are very common according to Some AI pilots who interviewed for this following article but I have no idea of the authenticity of this report:

https://www.rediff.com/news/report/a...h/20250613.htm "The Air India pilots also added that Ahmedabad airport has long been known for bird activity near the runway, which could have contributed to the incident.

"This issue (of the excessive presence of birds) has been flagged multiple times," a third Air India pilot said, asking not to be named."
Of course, a single engine failure would not have brought this aircraft down, nor would it have deployed the RAT, but we can't see what happened on the left engine when the aircraft slipped behind the radio antenna building.

While these high bypass engines are designed and certified to keep running after experiencing certain types of bird strike, the effect on two engines concerns have been voiced about the contribution of certification to the mitigation of the risk hazardous bird strike in the two engine case.

This from Sky Library:
https://skybrary.aero/articles/aircr...nue%20to%20fly .

" A number of concerns have been quite widely voiced about the contribution of certification to the mitigation of the risk of hazardous bird strikes:

• The case of bird ingestion into more than one engine at the same time is not addressed directly and it is clearly extremely difficult to meaningfully estimate the probability of such an occurrence. However, it has been observed that, since some of the current standards only require that a damaged engine can be safely shut down, this circumstance should be more fully considered when determining the acceptable outcome of ingestion into single engines, especially for the twin engine case.
• It has been noted that the potential effects of bird strikes on modern electronic flight control systems and flight deck instrument displays have not yet been fully assessed.

Maybe someone can do some video enhancing of this image as others have done with the audio enhancement to give strong probability of RAT deployment.

If my suggestion can be corroborated at all, then the question of what happened next becomes somewhat easier to answer. Perhaps neither engine stopped running but they did so with limited thrust? If anything from the pilots mayday call can believed, it wasn't engines shut down..it was no thrust. So why did the RAT deploy? Cant answer that. And, I cant imagine it would be manually deployed if both engines were still running.
However, TDR did say.

"On the 767 and 747-400, when you shutdown an engine and the IDG goes offline, there is a momentary 'glitch' in the electrical power system as it reconfigures for the available power source - this is why you see the flight deck displays flicker and return, and the cabin lights momentarily flicker."

Startle factor that electrically systems were about to fail? Manually deploy RAT?

Edit: I might add, they would have found remains on the runway if this did indeed happen. But we have heard anything from anybody?

Question to avionics specialists again. Below is the main drawing of the TCMA subsystem, included in the patent document . I can't stop scratching my head about the link I have circled in red in the center of the image. AFAICS, this link shunts the internal RUN path of TCMA entirely : the RUN signal is supplied by the RUN contact of relay assembly 52, then goes through the common and RUN contacts of relay 22, then goes through the common and RUN contacts of relay 28, then exits TCMA subsystem 18 by wire 124, and... we're back to square 1, because of the link. So TCMA subsystem 18 doesn't actually control the OPEN relay 118 of the HPSOV, only the CLOSED relay 100, and in the case where relay 22 and/or 28 are activated, both coils of HPSOV could even be energized at the same time.

Obviously enough, this isn't a real circuit diagram, but shouldn't this link be removed from the patent drawing?


Odd link in TCMA patent drawing

Good catch. When I quickly scanned the drawing, I stopped when I realized that it wouldn't tell me how the function actually works in the real world \x97 pretty normal for patent applications. Unless I misunderstand (it happens), I think you're right. That link doesn't make sense.

In the CSV data set that can be downloaded from that link the first point with altitude data is 1630 ft short of the departure threshold. That point is 575. The highest alt recorded in the data set is 625. All the points with altitude data overlay the departure runway. I do not understand how anyone is using this data set to determine the maximum altitude which was way past the departure end.




Edit to add - I have made no attempt to correct the raw ADS-B altitude data. There is no need to make any correction to see altitude gain.

Yes, we know it climbed. I suggested use of the granular data to show how high it was, in the context of the 400ft mode changeover point.

I don't have access to a current 787 manual, but have found a couple of unverified references to the VNAV engagement on the net. It appears the VNAV will engage at 400ft also. Happy to be corrected though.

Level-off point, approx 11sec after liftoff:
​​​​​​​

Could you please elaborate on that?

FR24 did do that raw ADS-B data comparison. Remember the GPS position and barometric altitude are sent by the aircraft itself. The altitude is sent in 25 ft intervals, so a shallow curve that is smooth in reality looks janky in the data, due to the rounding of the numbers. From https://www.flightradar24.com/blog/f...rom-ahmedabad/ :
The red line is the accident flight, and it covers approximately 4.3 seconds.
Obviously the altitudes are all uncorrected for barometric pressure, which would've varied with the weather on that day; you kind of have to mentally shift the lines vertically downward. Now I looked for, but couldn't find, the post in the old thread where the rotation was triangulated\xb9, but I remember that it was near the turnoff to the high-speed taxiway, so a few seconds ahead of this ADS-B capture. We only have the video to show us what occurred then.

That means the ADS-B data doesn't really tell us whether the first few seconds of the climb were normal or not.

When we compare the red line to the blue lines, the data tells us the climb rate had already decayed significantly before the accident aircraft passed over the end of the runway, because the red flight path is much more shallow than the blue flight paths.

Please correct me if I'm wrong: to my eye, the data alone does not show that the engines must have failed after rotation, because the data does not demonstrate a normal climb rate.

But likewise, the engines can't have failed much before rotation:
For completeness' sake: you can look at the CCTV video, consider the 787's wingspan a flying 200 ft yardstick, and hopefully agree that the aircraft did not get much higher than 200 ft AAL, if that.

-----
\xb9 I found one of them, anyway. The reference is the CCTV video:

I too was curious to see the donks but sadly all I've come across are indiscernible snaps of mangled mass

If anyone wants to read an article that is paywalled, many browsers have a speed reader function. If you select this as soon as the page loads it will often open a simplified page, minus some graphics, but all the text should be readable. Nothing in The Times or Reuters adds anything we didn't know.

Hmmmmm\x85.then I wonder how the auto throttles will behave if a low stop height if the MCP is mis set \x97 potentially below 400\x92 AGL. Will they stay in hold, will they go to SPD, or will they engage in THR REF.

I never tried this in the sim on the 777 so I\x92m not sure. I was grateful that the 777 would change to SPD mode on initial altitude capture (as opposed to the -400 VMo here we go). It\x92s been a few years in any case though.

Usually on takeoff LNAV and VNAV are armed. During the takeoff roll the autothrottle system goes in to HOLD mode at 80kts.

At that point the FMAs read:



At 50' LNAV engages and the FMAs change to:




At 400' VNAV engages and the FMAs change to:




The height is referenced to a barometric snapshot taken during the take off roll at 100kts.

If an altitude is captured before VNAV engagement (totally bizarre to capture an altitude of less than 400') then the FMAs would change to:

SPD | LNAV | ALT

I still consider the forward truck tilt is a massive clue to a C system Hydraulic failure prior to wheels-up, which must have been caused by loss of electrics (since C is solely electrically powered), so I am still wondering if hydraulic failure happened before or after the loss of thrust.

While thinking about the consequences of a total hydraulics failure around time of rotation (caused by a suspected dual engine failure), here is a new observation. I searched the previous threads to see if anyone lese had noticed it.





In the rooftop video, as it's just approaching the treeline, there are spoiler deflections visible just behind the engines on each wing.

With a total hydraulics failure, the pilots control column using direct wiring, will only control this spoiler pair and the stabiliser. The RAT does not control this spoiler pair (hydraulically), only the most inboard spoilers pair. Its an interesting observation because it means this spoiler pair were being deflected electrically, either by the battery or RAT. But if the RAT provides emergency C hydraulic power why didn't the RAT powered spoilers deflect instead? Does this mean the RAT was unable to provide emergency hydraulic at such low airspeed?

I think this also re-affirms the critical loss of power (dual engine failure), and rules out many other theories. It tragically lost all power, both engines, all hydraulics and electrics (apart from battery and RAT).

I am wondering if anyone else has noticed other flight control deflections?

(Tried posting link to youtube but unhelpfully frames entire video)

Thanks much — pretty much same as 777. Was wondering if someone had set MCP to 200 in error what autothrottles would do. What I’m wondering is if the aircraft were being hand flown to a low capture like that if the autothrottles would initially pull power back from THR REF to anticipated level off setting for SPD which would be bug speed (V2 to V2+15). And might be a fairly dramatic reduction of power. Granted since its speed on autothrottles at some point power should come back up. But I wonder if the autothrottles would respond to what they thought for level flight initially.

Could explain the witnesses thought that power came back up before they hit but witness recollections post traumatic event as well as second hand reporting need some time to settle in before accurate facts come out.

A naive glider pilot question: if fuel cut off was (inconceivably) selected, would both fuel control levers have been flipped downwards from Run to Cutoff? And if they were then immediately flipped back to the Run position, how much time would have been needed to achieve enough thrust to maintain altitude?

On the B777, each EEC is powered by a dedicated control alternator whenever the engines are running. The control alternators are mounted on the forward side of the main gearbox of each engine.

The flight controls power supply assemblies (PSA) have several sources of power, including PMGs located within the backup generators.

The EEC control alternators do NOT perform double duty by powering the flight control system PSAs. I can't imagine the B787 being much different.

Unfortunately not available in the US. This is what I see: