Posts about: "FDR" [Posts: 113 Pages: 6]

The pilot is dead, hence, we cannot ascertain that without the pilot having reported or spoken about it. If the CVR has no word on it, then anything the FDR shows in manouvring that suggests this, will forever be speculation.
That suggests to me myself, ethically, that we limit speculation on the intent of the pilots when it comes to things this ethically charged unless there's good evidence on the FDR. Rest in peace.

The only aircraft inputs to TCMA is air/ground and thrust lever positions - everything else is the FADEC and its sensors (primarily N1). Even if air/ground was compromised somehow, it would take other issues before TCMA could possibly be activated. Possible on one engine (although remote) - but two engines at the same time - almost literally imposssible (unless of course it's software error).
The 'good' news is that even a cursory check of the FDR will indicate if TCMA activated, so we'll soon know.

Re FDR and CVR, remember the 787 uses EAFR(s) instead - one in tail and one in nose.

Comments above "they will already have been read" - suggest search and read India press links, and the (new) India AAIB lab ability to read data recorders, e.g. one timed at June 15, 2025 00:08 IST. It may well be the first 'political' issue about this accident in where the recorders are sent. If India is chosen, maybe they will take their time with a new lab, and watched over by the world and other AIB representatives? I believe the investigating state 'controls the release of information' (or not). Whilst the UK AAIB are there, as their website says they have 'expert' status, which I suspect means not a lot of involvement in the politics.

Gear and flaps are both hydraulic, and the hydraulic pumps typically act as effective fault-containment - a hydraulic failure or excess load doesn't result in excess demand on the electric side; the pump just starts to run out of output flow/pressure.

In addition, the 787 has four main generators and I believe the switching is segregated into at least two controllers, on top of the four separate generator control units.

And again, electrical failure should not cause engine failure - consider QF32 where the wiring to the engine was mostly severed and they had to drown it with a fire truck.

It's not. Boost pumps should be more-or-less unnecessary at sea level.

I believe the valves are almost all bi-stable power-open power-close. When not powered, they remain in the last commanded position.

The valves are located in the spar (hence being called 'spar valves'. The fuel tank is immediately above the engine so it is a very short pipe for suction feeding. Tail mount engines are potentially a different story...

A Prelimnary Report must be prepared within 30 days, but does not need to be public. May or may not have CVR/FDR data.

I agree. The subject aircraft was fitted with two Enhanced Airborne Flight Recorders (EAFRs), one of which is located forward and one in the rear. These recorders capture both voice (traditional CVR) and data (traditional FDR), and provide redundancy. One - presumably the one in the rear - has already been recovered.

Two weeks is likely long enough for the investigators to determine if a systems failure might, in any way, have been a possible cause. I am sure that if there is any reason to suspect that a systems failure may have been a probable cause, or even contributed in any way to the accident, Boeing, GE, the FAA, or the Indian DGAC will promptly advise 787 operators.

This is assuming too much. There are legal and technical reasons why the CVR may not have been downloaded yet or, if it has, why no information has been released.

In an ICAO Annex 13 investigation, interested states and experts are invited to participate. In this investigation, investigators from the US and UK are participating (there may be others as well), and experts from Boeing (and possibly component manufacturers) have also been invited. The lead investigators will often hold off on recovering data from the CVR and FDR, or examining the data, until there's agreement between the interested parties on how to go about doing it. With the distances involved, travel logistics could easily delay examining the data by a couple of days.

In some cases, the board leading the investigation doesn't have the internal expertise to recover data from the CVR and FDR. In these cases, agreement needs to be reached on which technical experts are going to take the lead on recovery. I don't know if the Indian AAIB has internal expertise or if they need to find external expertise to recover the data.

In some cases the CVR and FDR can be damaged and technical experts need time to come up with a plan to repair the recorders and recover the data.

Annex 13, Article 5.12 prohibits the release of CVRs and analysis/opinions from FDRs, unless the investigators decide that the benefits of the disclosure would outweigh the adverse impact that release would have on future investigations. This rule exists to encourage full cooperation in investigations from participants in the industry, including pilots and operators. India's accident investigation rules are consistent with Annex 13: see section 17 of the Aircraft Investigation of Accidents and Incidents Rules, 2017. So even if the CVR and FDR have been analyzed, it may well be that information isn't being disclosed to the public because they haven't reached any definitive conclusions yet that they're confident will end up in the final report.

The investigators will certainly soon know, but how sure are you that they'll share that in public?

Nope, you may not have read the whole thread - the full set of conditions which can trigger the RAT have been posted multiple times before your reply

I'd phrase it differently: the frequency (and harmonics) of the noise are consistent with it being a RAT. If you then assume that it was a RAT and infer distance and speed curves from the Doppler variation, you get plausible values for an aircraft. But the two things are somewhat linked so you can't really treat the second thing as confirmation of the first. (FWIW, I'm personally quite satisfied that it was indeed a RAT on the audio.)

Presumed or reported? If the latter, by whom?
I do not intend to single you out, but I want to illustrate something with this response.

A lot of discussion on this thread has pointed toward two engines failing - or losing power - for a variety of reasons.
PPRuNe members are analysing and discussing this tragedy.
When a credible report comes out that says you, or we, can say that engines were shut down or failed.

Using unconfirmed news reports, social media, or PPruNe analysis as a basis of "fact" is hazardous.
A number of posters succumbed to this: see the obsession over white and green lights at the exit door (near seat 11A) as but one example.

As an aside: your EFATO story might be of interest on the Mil Av forum.

A Qantas 747-438 suffered an 'Electrical System Event' when on approach to Bangkok airport on 7 January 2008. The following extracts are taken from the report:

"System malfunctions

Between 0846 and 0852, 4 after passing FL 100 and when the aircraft was turning
onto an extended left downwind leg for runway 01 Right (01R), the EICAS, flight
displays and automated systems showed faults of numerous electrical and other
aircraft systems, including:
\x95 AC buses 1, 2 and 3 not powered
\x95 autothrottle disconnected
\x95 autopilot disengaged
\x95 some fuel pumps not operating
\x95 weather radar not operating
\x95 automatic cabin air conditioning and pressurisation system not operating
\x95 right (FO\x92s) displays blanked
\x95 between three and five pages of messages on the EICAS display
\x95 lower EICAS display blanked.
The CSM contacted the flight crew and advised that the cabin lighting had failed."

"Origin of Generator Control Unit (GCU) faults

Post-incident examination of the GCUs revealed corrosion of the internal circuit
boards in all three of the GCUs that shut down. Analysis of the corrosion materials
observed in GCU 3 showed evidence of long-term exposure to water, including
evidence of acids and carbohydrates that are present in beverages such as coffee,
fruit juice and soft drinks. Those findings indicated a fluid source originating from
the aircraft\x92s galley drains or from spilt liquids in the cabin, and also suggested that
liquid ingress had been occurring over an unknown, but extended period of time."

https://www.atsb.gov.au/sites/defaul.../ao2008003.pdf

This link to the report includes diagrams of where the 747 forward galley was located, directly above the Main Equipment Centre and the E1/E2 racks.

The phtographs show how ineffective the dripshield was in protecting the electrical equipment and the extent of corrosion and damage.

The aircraft was 17 years old at the time of the incident and had completed a C-check approximately three months before the incident.

As FDR notes, this issue seems to have carried over to the 787-8 with Airworthiness Directive AD 2016-14-04 ( https://drs.faa.gov/browse/excelExte...A0058AF6B.0001 )

"We are issuing this AD 2016-14-04 to prevent a water leak
from an improperly installed potable water system coupling, or main cabin water source, which could
cause the equipment in the EE bays to become wet, resulting in an electrical short and potential loss
of system functions essential for safe flight"

AD 2016-14-04 mirrors precisely what occurred to the Qantas 747 on 7 January 2008. It is possible something similar may have occurred on take-off of AI171, with water causing the equipment in the EE bays to become wet resulting in electrical short and potential loss of system functions

OK, another hour spent going through all the posts since I was on last night...
I won't quote the relevant posts as they go back ~15 pages, but a few more comments:

TAT errors affecting N1 power set: The FADEC logic (BTW, this is pretty much common on all Boeing FADEC) will use aircraft TAT if it agrees with the dedicated engine inlet temp probe - but if they differ it will use the engine probe . The GE inlet temp probe is relatively simple and unheated, so (unlike a heated probe) a blocked or contaminated probe will still read accurately - just with greater 'lag' to actual temperature changes.

TCMA - first off, I have to admit that this does look rather like an improper TCMA activation, but that is very, very unlikely. For those who don't know, TCMA is a system to shutdown a runaway engine that's not responding to the thrust lever - basic logic is an engine at high power with the thrust lever at/near idle, and the engine not decelerating. However, TCMA is only active on the ground (unfamiliar with the 787/GEnx TCMA air/ground logic - on the 747-8 we used 5 sources of air/ground - three Radio Altimeters and two Weight on Wheels - at least one of each had to indicate ground to enable TCMA). TCMA will shutdown the engine via the N2 overspeed protection - nearly instantaneous. For this to be TCMA, it would require at least two major failures - improper air ground indication or logic, and improper TCMA activation logic (completely separate software paths in the FADEC). Like I said, very, very unlikely.

Fuel contamination/filter blockage: The fuel filters have a bypass - if the delta P across the filter becomes excessive, the filter bypasses and provides the contaminated fuel to the engine. Now this contaminated fuel could easy foul up the fuel metering unit causing a flameout, but to happen to two engines at virtually the same time would be tremendous unlikely.

Auto Thrust thrust lever retard - the TO lockup in the logic makes this very unlikely (it won't unlock below (IIRC) 400 ft., and even that requires a separate pilot action such as a mode select change or thrust lever movement). And if it did somehow happen, all the pilot needs to do is push the levers back up.

Engine parameters on the FDR: I don't know what exactly is on the 787 FDR with regards to engine parameters, but rest assured that there is plenty of engine data that gets recorded - most at one/second. Getting the FDR readout from a modern FDR is almost an embarrassment of riches. Assuming the data is intact, we'll soon have a very good idea of what the engines were doing

The only aircraft inputs to TCMA is air/ground and thrust lever positions - everything else is the FADEC and its sensors (primarily N1). Even if air/ground was compromised somehow, it would take other issues before TCMA could possibly be activated. Possible on one engine (although remote) - but two engines at the same time - almost literally imposssible (unless of course it's software error).
The 'good' news is that even a cursory check of the FDR will indicate if TCMA activated, so we'll soon know.

Something that occurred to me after I went to bed last night: My assumption that the FDR readouts would rapidly reveal the cause may be flawed.

Let me explain.

The consensus is that both engines quit shortly after liftoff (that assumes that the RAT did in fact deploy). At least one of the data recorders has battery backup, so it should have kept functioning when all aircraft power was lost.

However...

Over the years, I've looked at lots and lots of digital flight data recorder outputs when investigating some sort of incident or other engine anomaly, So I have become rather familiar with some of the interesting characteristics of DFDR data.

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. As a result, most of the avionics boxes 'reset' - this is quick, but it's not instantaneous. This shows up in the FDR data - sometimes as 'no valid data' for a few seconds, or as garbage readings of zero or 'full scale'. Now, looking at the FDR data, it's easy to simply disregard the data, so normally no big deal.

Starting with the 777 (and on the 787 and 747-8), this electrical power glitch was 'fixed' - there is slight delay (~quarter of a second IIRC) before the fuel cutoff signal is sent to the engine - during which the electrical system reconfiguration takes place so no more 'glitch' during a normal engine shutdown...Except whatever happened to these engines wasn't 'normal'.

If there is a fuel cut at high power, the engine spools down incredibly rapidly - a second or two from max power to sub-idle. Assuming the fuel cut wasn't commanded by the flight deck fuel switches, the electrical system won't know it's coming, so it can't reconfigure until after the engine generators drop offline - and you're going to get that power glitch. Nearly every avionics box on the aircraft will reset due to this electrical glitch, and the FDR isn't going to get useful data for a few seconds (and then, only from the stuff that's on the battery bus).

Whatever happened, happened quickly - it's quite possible that whatever initiated the high-power fuel cut didn't get recorded.

True, I would bet that the voltage regulating architecture of the voice recorder at least will give useful information for a short time around the loss of power, as it did for the Lockerbie CVR using far less sophisticated recorder systems. That was sufficient to show the pressure pulse in the fuselage and to give a fairly good idea of where the explosion had emanated from. TWA was similar, a bigger bang though. Would be listening for any mechanical noises related to the fuel switches, and frankly I doubt that they existed, but they would be recorded.

If the cause is what I have suggested it will dificult to get direct evidence of that case, as it was for the QFA072 event as well. Like icing cases, a water ingress into the avionics is going to be a tough investigation, water would have been sprayed all over the wreckage in the aftermath. Dousing the E/E bay with 20 or 30 gallons of water will be an expensive investigative exercise to do in a real plane, with engines running. Would not want to be observing up close.

Not a pilot, but an engineer with some experience in accident / incident investigation.
One thing that strikes me in this and the previous closed threads is the lengthy back-and-forth discussion about potential technical faults that could lead to this accident.

However, there has been relatively little discussion about the #1 cause of all airplane accident - pilots' mistakes.

Except for the initial conversation about mistakenly retracting flaps instead of landing gear, which eventually was dismissed in favor of engine failure as there has been an almost unanimous agreement that even if such mistake was made, it was recoverable.

But what if the pilots made more than one consecutive mistakes?

Mis-diagnosing the first abnormal behavior and making things worse by performing another action that instead of correcting the first mistake, turned the situation unrecoverable. The history of aircraft accidents is full of examples when a first, relatively benign issue was made much worse and eventually tragic by pilots' subsequent actions.

Frankly, I think it is much more likely that the pilots made several consecutive mistakes than eventually led to the crash than a 1-in-a-billion unrecoverable mechanic failure. I'm looking forward to the CVR and FDR transcripts and I suspect that we will learn that after whatever happened first (pilot's mistake or minor technical failure), it was subsequent pilot's action that turned a manageable situation into a tragic accident.

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?

Thank you for confirming.

This is not only happening to the FDR but to any reciever on the data busses. And likely not only when the engine spools down and power supply switches but also when power busses come offline and bus bar breakers activate or in any severe fault in the electrical system involving large currents, possibly arching shorts.
Hence my comments on SISO and input filtering and verification in the closed thread.

Pooled water around the moisture barrier is just looking for a suitable access point to drain into. The 3 events I am aware of in the B744 were all during manoeuvring, 2 at rotate and one during a descending turn.


Presumably they must also supply that information to the FDR at least, but I don't know how.

The flight recorder on the 787 is called "enhanced airborne flight recorder" (EAFR), and it's a combination unit with CVR and FDR functionality. There are two on the aircraft, the one in the front has battery backup.
Since it has been reported that the "FDR" was found, they also have the "CVR".

B787 Skipper.... No longer able to sit on my hands!

The joker that published one or other of the fictional accident reports before the dead are even identified needs stringing up by the thumbs.... Well done mods. OK, some of these theories, just bearing in mind the the flight recorder (there is only one FDR + CVR combined) was in the intact section of the undamaged tail and has been with the authorities for almost five days......

- All you guys who are rushing down the TCMA rabbit hole: If it was established that a software error drove both engines to idle without warning, after rotate.... Don't you think the worldwide fleet of B787s would have been grounded by now? Such a glaring failure would be absolutely inescapable on the FDR.

Whatever was wrong with this aircraft was present at rotate, unbeknown to the crew. The fact that no ADs or notices to operators have been issued usually means that the cause is known and the aircraft was serviceable. The statement from a prominent Indian Captain about the skill and tenacity of the crew, right up to the last minute is absolutely laudable. However, the cynic in me says that the way is being paved for some bad news and by that I mean news that will do Air India reputational damage. Expect more management of expectation in the coming days.

I'm still going with
a) Incorrect derate + low Vspeeds or
b) Low altitude capture