Posts by user "Kraftstoffvondesibel" [Posts: 38 Total up-votes: 314 Pages: 2]

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.

Alright, just because that isn't very difficult. The first segment is a Moped/motorcycle whizzing past. Not from the same city, but it is in India, and I listened to a number of them to find a representative one, and the closest I could find in lenght/timing that isn't completely out of bounds with the streets in the area the AI video was filmed. it is taken uncompressed from a professional sound library and is a very high quality recording. The sound source is in direct line of sight, much like the AI recording when the aircraft is presumably just coming into the clear from above the roof. A moped/motorcycle in the AI video, would probably not be direct line of sight down on the street, and would have an even more ambient character, but shorter ambience. The second segment is the Air India video.
One thing we haven't discussed as a characteristic is how the AI recording moves from indirect sound with a shorter ambience, to direct sound, to a very much more ambient distant character in the same amount of time as the large aircraft moving overhead.
The moped/motorcycle in the sample, keeps about the same small street ambience throughout.
Notice how the harmonics are in different places with different spacing and with different relative intensity, the emphasis on the internal combustion engine is lower in frequency than the open Rat, but with added exhaust noise.
Thank you.



I also enclose a doppler distance

So, also as an outsider when it comes to cockpit engineering, there is one commmon "system" in the sense of the very close physical location, the two engine systems have in common, and that is the physical cut off switches and their behind the panel connections.

It wouldn't take a kids pool of liquid to intefere with those?
(I asked this question previuously, in the middle of a long text, but the discussion had a very different direction then.)

What are possible ways of a common failure/triggering of these contact points somewhere in their physical installation in the cockpit?
Remember when the A350 had to be modified only 5 years ago to not allow coffee spill to turn off engines.
What about the same location in the B787?
What are the actual switches? Are they purely traditional electromechanical contact switches? How do they make contact, ie. what are the actual gaps and dimensions? Are they digital in some sense? How are they protected? Are both installed the exact same way, or are they installed with different physical screening/protection/orientation as so to make the failure modes different? How are they physically kept apart, isolated from each other to avoid interaction and/or common failure. What is the physical distance involved there? What about the cables and connectors to them? separate or bundled in the same wiring harness? Or even in Mil or D-sub connectors? I find one description of them as a common(both in one box) line replaceable unit with quick connects. Both of them in the same unit with a common connector? Sounds wild if so!
Just had to ask, and hope it doesn't disturb the great discussion too much.

But what about whats inside and behind the switches? How is the signals from them transmitted to the valves? Analog? Digital? Software? They seem to be part of the same LRU, what does it look like on the inside? same multi-cable harness too? Same multi-connector? I believe this has not been touched upon.

The spec sheet says 100,000 cycles.
Switches fail sometimes. I have changed lots of lots of malfunctioning toggle switches in my day.
But both at the same time?
It has to be a common thing happening at the same time.
Someone slipping both switches into a worn middle detent is such a thing though, that is one habit that could be developed. A slight bump at takeoff and they both go to cutoff.
Or they are worn and theres an iphone behind the throttles, as someone mentioned.

The switches themselves are on-on 4 pole toggles, and doesn\x92t fail into one position over the other, and gravity would prefer the cutoff position in this design.

I mentioned I have used my share of switches, knobs and buttons. In much larger quantities than what you find in aircraft, but without the life and death factor, and thus no SOP.

Unexpected things happen, no one dies, but I myself brodcasted jolly sounding very inappropriate intro music over a very dark news report on the unravelling Joseph Frietzl case by dropping my phone on a switch. Several million viewers, a good chunk of which called to complain.

Grave errors can be banal.

Other than that, common connectors, the harness itself, I have seen a large amount of unexpected electronic things happen when those get bendt the wrong way.

Absolutely. Like a badly tightened connector, or a harness short waiting to happen. I only mentioned some possibilities.

Since these kind of switches has been in operation for about a century now, it would absolutely be a statistic outlier. But this case surely is just that either way.

Yes, seems like they also come in a on-off-on version, but the thing is what could happen when the mechanical function is worn, which is a thing with switches used over time in real world scenarios.

It seems the design, function and placement of these switches might have been \x93grandfathered\x94 over several generations of cockpit design.

(re:skwdenier and the photo of the switch. )
And those wires, which all i can find points to having (non-english speaker) screw terminals. within the LRU shared by both switches. Those things go bad over time even when installed in non-movable equipment.
For those that argue that these are some kind of very special switches. They aren't. Sure they are really nice switches, but that series is available through normal distributors like mauser or elfa-distrelec in europe for, and the price isn't sensationally high compared to other switches.
I am curious as to how the LED light power is threaded through to the switch top. Why do they have a LED, in the first place? Seems a bit gimmicky.

Since they have such inherent damage potential in systems that are otherwise carefully isolated through redundancies and physical seperation, why aren't they? Why aren't the 2 cut off switches placed in 2 different locations in the cockpit. Seems like such a cheap insurance.

Sorry if I am adding noise, I know these are just one of many possibilities, and I am not knowledgeable enough to weigh these different theories against each other, but this switch thing is just something I know personally have more failure potential than what I thought were acceptable for this application.

Thanks, you read the specs better than me, and the LED being connected to the fire indicator is a nice ergonomic detail.

It would surely be nice to get clarified. Does the FADEC control the fuel cut-off valves? Isn't that messing up the hierarcy somewhat? And wouldn't/shouldn't these be separate from everything else?
If so , the likelyhood of this having anything to do with the switches, their harness, or connectors drops way down. (although most theories are dealing with statistical "impossibilities", what better time than after decades for such to occur.)

The switches are double on's or 4 pole, that means they are (can be) connected to 2 different systems individually. Anyone know how that system looks? Why 2 signals?

Regarding the Recorders, obviously nothing to do with the cause, but still:

Given:
There were 2 recorders:
1/in the tail, likely to not be overly damaged, but might have stopped being powered at the moment the thrust was lost. Due to digital delay, it might not have catched interesting transient data of the cause.
It is too far removed from the cockpit to have independent analog feeds from microphones or other equipment.

2/ The one in the front, much more likely to have been damaged, and also more likely to be useful because it had an independent area microphone cockpit source.

I have 2 questions and a speculation:
Speculation: The front recorder also lost all data because the systems powered down, except it independently, and by analog direct means, powers the cockpit area microphone w/micpre and could continue recording that for a good amount of time on a small battery.

This then might be the recorder recieving special treatment and delayed read out, because of the damage, and because it contains audio from the cockpit, (while the other one, might already have been read by conventional means, but doesn't contain anything of use because this was a sudden event and digital latency. Or as I assume some might speculate, the tail recoder hinted to information leaving the decision on whether to read the front recorder abroad to someone much higher up)

Questions:
1/Would the recorders lose access to aircraft data streams when engine power is lost, at least temporarely making the cockpit area mic recorded by battery power on the front recorder the only source of information ?
2/The recorders only draw 20W, why is it the front have reserves only for 10 minutes? Can you even buy a battery that small giving 28VDC? Why is such a limited solution selected?
(And since they have a microphone input, and the units are interchangeable why don't they just stick a few grams worth of microphone in the back of the aircraft as well, just to catch mechanical noises that could help when data input is missing. Audio sensors seems underrated.)
( For reference, This battery could power the whole recorder for an hour: https://www.batteryspace.com/custom-nimh-battery-28-8v-800mah-23wh-with-tabs.aspx )

The recorder data sheet specifies it is an analog input for the area mic, and that it and its pre-amp are powered by the recorder.
It is likely a mems-type microphone, moving coil, ribbon or traditional condenser microphones aren’t really used outside the stage or vintage recording studios these days. But something along these lines: https://pdf.aeroexpo.online/pdf/l3-t...html#open64169

Note the dual analog and arinc digital outputs.

One reason for not doing an analog line all the way to the tail would be weight, as you mention, quality or noise wouldn’t be an issue due common mode rejection.

I am starting to see the hamsterwheel references now.
Having two combined recorders is already more backup than what had previously been the norm, in addition theres the independently powered area mic going analog to the front recorder.

The common models I have checked the sheets for also provides a digital output (which is probably sent to the aft recorder via normal busses.

Having a seperate analog line going to the aft recorder would be several Kg of extra weight, and probably a substantial amount of loom design and paperwork for what is then a backup to an already redundant system.

Hence, imho why this signal only goes to the forward recorder. It is already a \xabbonus\xbb.

The power for microphone and preamp is in the >1watt range range, completely insignificant.

I am still interested in reliable information as to what is expected to be on the recorder of an aircraft which has lost the generators, what about the battery powered prinary instruments? Does some systems and the aft recorder come online with the RAT or would everything be down to the one cockpit mic? Surely not?

Not quite sure if this thread is open again or not.

I wanted to bring something up.
Maybe I am out of touch, but the way we have talked about this accident, we have talked about it like it were doomed to be an unsurviveable high energy crash inferno.
I, at least, have been guilty of having this picture in my mind.
Wasn't this a, relatively speaking, a low energy impact scenario, comparable to Air France 269, SAS 751, BA038, or a number of other accidents including things like the hudson river event, which would have been somewhat surviveable except the impact with the buildings?

There looks to be more open areas in close proximity to the accident site that are as big, 150-250 meters, or larger than what either of those others had available or at least used.
There have been comments of the docile trajectory of the aircraft being a sign of pilots giving up, and letting automation take over of sorts, but in reality, could it be they just did exactly the same as the crew on BA038 or SAS 751? Except the lack of luck?

In connection with this, why would the recorders be so damaged it has taken them weeks to access them. It seems that kind of impact should be well within the envolope for those designs.

If out of bounds or order, please delete.

I think we have been through this several times just over the last few pages of the thread: the (front)recorder is battery powered for ten minutes, and it also independently powers, amplifies and records a cockpit area mic through it\x92s analog input. The recorder\x92s power consumption is only given for the unit as a whole and is incredibly low. You can hardly find a commercially available battery that is too small to power the thing for 10 minutes.

What potential other data reaches the recorder to be recorded in the first place in a emergency power situation, is the relevant question that has been asked about 30 different ways, but has not been answered. It might be none.

This has also been touched upon earlier in the thread, but it rather seems the cut-off switches are in the same LRU, in close proximity, using the same connector and goes through the same wiring harness. No one was able to say whether it works purely by digital signaling, and goes through any common software, or if it is duplicated by purely direct signaling. There might be numerous failure modes of the cut-off switch design, it is obviously very, very robust and overall sound, since dual failures here have never happened, but this is alredy an outlier event.

I did look into this while analyzing the audio for RAT confirmation, but I did not conclude with anything other than that the engines where clearly not at any kind of take off power.

I did not find good enough material to compare to, and time was lacking a bit.

There is engine noise, or engine-like noise from there, somewhat comparable to an engine at idle, that fades out into the background noise at the same rate as the RAT. I don\x92t know if it comes from an engine at idle, windmilling, an engine producing some power, or if it is even just aerodynamic noise from the rest of the airframe.

I\x92ll give it another go if time allows.