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

And each FADEC is unique to the engine in which it is hosted. So whilst these may be "autonomous" they still rely on data external to the engine itself such as WoW and Rad Alt where they hold more "sway" than they do in the flight deck.

Are these values recorded in the FDR?

Are values from the FADEC recorded?

You'll hopefully not be surprised to learn that there are many, many people asking the same questions at the moment.

The excellent #724 post by user989 really should be seen as the defining statement on what is currently known.

I’d like to add a complimentary test to user989’s logic on TCMA faults.

Regardless of whether the ‘aircraft on ground’ signal was incorrect after rotation it would have been correct during the takeoff roll. IF there was an unrevealed fault in a thrust lever position signal THEN why didn’t TCMA activate during taxiing or the takeoff roll?

Such a fault occurring spontaneously in just the few seconds after rotation is way way down the probability table. Such a fault occurring spontaneously on both separate (think ETOPS) engine control systems is surely vanishingly unlikely.

They may be out there but you’d have to ask if TCMA is implicated where are the lower consequence precursor events in the 787 fleet? These might be spurious TCMA action on one engine or faults with ‘aircraft on ground’ found during maintenance or engines not responding to thrust lever position and so on.

Change Analysis would ask what happened differently in the few seconds after rotation on this flight that separates it from all other 787 takeoffs and why at that particular time ?The interim report will provide some answers until then please let’s confine this thread to fact based technical discussion and debate.

Re-reading this I did briefly consider suggesting engine overshoot of thrust lever positions and FADEC shut down on N1 overspeed but that leaves a lot of WHY and WHY both engines questions so I dismissed it.

For Cloud Chasing:
Which media sources? (Article source and date would be helpful).
Any number of posts in both threads have offered the estimation that the flight would have not had additional fuel, and thus a "fill all the way up with fuel" assumption wasn't warranted.
If the reports you mention are credible (rather than mere speculation and rumor) that would be of interest.
The actual fuel load will, in time, be known once the FDR info is processes in full.

Yes PLEASE! I'm a Journalist and a (Private) Pilot and find it incredibly frustrating when people post quotes from "sources" without revealing the source of the quote with a link to the original article. No link? I ignore the post.

There is way too much misinformation floating around nowadays and I don't want to read it on this forum. PPRUNE has been a fantastic source of knowledge for me personally - especially leading up to my PPL exams in 2006.

Back then I could trust much of what I read on here. Thankfully the mods do a fantastic job and manage to weed out most of the nonsense but it takes time and I think it puts off many of the legit professional flyers from posting here.

What also winds me up is the amount of posters including YouTube links to dubious channels invariably presented by old blokes wearing epaulettes and claiming to be professional pilots. I wish these links could be banned. YouTube is not a source of news. It's a public website where anyone can post any old rubbish and pretend that it's real when it isn't. It worries me that so many people assume that "because it's on YouTube it must be correct"!

And FR24. It's a commercial website for aircraft spotters. It is not an accurate source of information for professional flyers. If I see a poster linking to it I ignore them as well.

It really is quite difficult now to "sort the wheat from the chaff" particularly on threads devoted to aircraft accidents. Thank you MODS for making it slightly more bearable!

The available video and trajectory information are quite conclusive that both engines stopped producing thrust within 12 seconds of the main wheels leaving the ground. Had partial power of any level remained, the aircraft impact would have been further away from the departure end of the runway. The NE end camera shows by using transit sightings against identifiable structures, that the failure occurred while the aircraft was still within the airport boundary area. The energy state of the aircraft at that time trades off to impact at the correct time and place.

On departure at these weights the aircraft would have some assumed temperature thrust reduction from max available on the GEnx -1B70, Unless they were carrying lead, they were around 30,000 or more below the limit weight for a flaps 5 TO. At that weight, around 440k lbs, they would have had a fair OEI climb gradient on one engine, certainly a positive gradient with the gear down, so they lost more than 50% of total thrust. There is no yaw or roll, or inputs to counter a yaw or roll moment so the aircraft was symmetrical at all times, that means losing absolutely no less than 50% of total available thrust at that point on each engine. At 50% reduction. the aircraft would have continued a positive gradient with the gear down and the flaps at the TO setting. It did not, it decelerated at around 1meter sec, or 0.1g deceleration for just maintaining level flight, but it also had to descend and that was worth around 0.05g as well. Instead of having any positive thrust margin, the guys were needing to descend to balance the decrement in thrust of around 0.15g, and that means it has negligible to no thrust from the engines. The full analysis takes more effort as the AOA has increased over the 15-20 seconds to impact, which is increasing the drag of the aircraft rapidly towards the end. For the first 5-10 seconds however, it is not such a great change, but it is still increasing.

In level flight, the aircraft would accelerate level at around 0.3-0.4g gear down with both engines running at max chuff. Lose one, and you are back to 0.05-0.1g or so. These guys had far less than one engine remaining, gravity was all that they had going for them.

To that end, there is no requirement to have the EAFR readout of the N1, N2, FF, or EGT, the video shows they had no puff going worth a darn. That is basic back of the envelope physics and anyone who does aircraft performance testing would be able to get that answer straight from the video without using a calculator, by the time they had watched the video a couple of times in replay.

I have no qualms on stating that the engines are not operating, the RAT, gear tilt are consistent with the dynamics of the aircraft. This is far simpler to determine the energy state than that of the B738W at Muan, the lack of early video required a couple of iterations of the kinetic energy of the aircraft at Muan to end up with a probable flight path, and most likely estimate of the thrust remaining for those most unfortunate souls.

regards,


FDR

SLF Engineer (electrical - not aerospace) so no special knowledge

Perceived wisdom may be applicable in normal circumstances but not when all the holes line up.

For example I've seen it quoted many times that the engine FADECs are self powered
by the engines, the TCMAs-whether part of the FADEC or a separate unit, similarly self contained
within the engine. The perceived wisdom seems to be that there is no common single fault
which can take out both engines.

And yet we're also told that the TCMA function can only function in ground mode and receives ground-air
signals from a combination of inputs from Rad Alts and WOW sensors.
There is therefore a connection from the central EE bay to the engine.

Yes I'm sure the Rad/Alt and WOW sensor processing will use different sensors for each side and powered from different
low voltage buses.
However as an analogy, in your house your toaster in the kitchen may be on a separate circuit from the water heater in
the bathroom, each protected by a fuse at the main switchboard. In normal operation a fault in one cannot affect the other.
However a lightning strike outside the house can send much higher voltages than normal operation throughout the entire
system and trash every electrical appliance not physically disconnected at the time.

Now I'm not suggesting the aircraft was hit by lightning but FDR has proposed a single event, buildup from a water leak entering
one of the EE bays at rotate. It would be possible for one or more of the HV electrical buses to short so that all the low voltage
buses go high voltage. I have no knowledge of how the FADEC / TCMA systems connect to or process the Ground-Air signals but
there is a single fault mechanism whereby high voltage could be simultaneously and inappropriately applied to both engine control systems.
It would be unfortunate if this failure mechanism did cause power to be applied to drive the fuel shut off valve closed.

Since the likelihood is that we're looking at a low probability event then perceived wisdom about normal operations and fault modes
might not be applicable.

They're not OK if they don't have the information on them that they "should" have had, aka they were stuffed, probably by a major electrical glitch, 4 minutes before the crash itself; they were blank from that point on.

Point taken about the radio.

They are both down the back in the A320 I think. The CVR was damaged and the FDR wasn't found for almost week after because it was blackened/camouflaged by fire, according to the press linked-to on Wiki.

But once these 'toughness' requirements come into play, having a brand new FDR lab, might not be sufficient in case you have to reconstruct the melted data access paths to the core memory modules, that indeed in all likelyhood survived.

Well if a brand new, completed in April purpose built facility is not up to the task, then what hope is there. That is why it was built, for just this eventuality. Knowing a little about things, I would venture that know how is more critical here than the equipment available.

Either way, the US facility is avaible, so why take a week to decide to send it there?

Here is their reasons…

​​​​​​​Some interesting words in there. Yes Minister.

The equipment on RAT/battery is limited:


(from the online 2010 FCOM)


(from the maintenance training )

The 787 battery fire report says the two recorders are on the left and right 28VDC buses. I don't think those get powered on RAT by the looks of it. I would wager you get whatever is on the 235VAC 'backup bus', plus the captain's and F/O's instrument buses via C1/C2 TRUs. You won't get all of that (like the F/O's screens) because the 787 energises/de-energises specific bits of equipment, not just whole buses.

Losing recorder power looks entirely expected.


400VAC/540VDC (+-270V) is not really known for blowing past input protection in the same way as actual HV or lightning. I would expect some optocouplers and/or transformers to be both present and adequate. There's definitely some big MOVs scattered around the main 235VAC buses.

Weight on wheels appears to go into data concentrators that go into the common core system (i.e. data network).

Presumably there is a set of comms buses between the FADECs and the CCS to allow all the pretty indicators and EICAS alerts in the cockpit to work. The WoW sensors might flow back via that, or via dedicated digital inputs from whatever the reverse of a data concentrator is called (surely they have need for field actuators other than big motors?). Either way, left and right engine data should come from completely different computers, that are in the fwd e/e bay (or concentrators/repeaters in the wings, maybe) rather than in with the big power stuff in the aft e/e bay.

At least one previous investigation report by the Indian AAIB has used CVR and FDR data downloaded from an (intact) EAFR.

With 'intact' being the crucial part of these recent posts. It is my understanding that a suitably equipped LAME can simply download the FDR data from an installed EAFR (CVR requires dismounting). So downloading as such, isn't the issue.

However more importantly, as implied by another poster 'patience' is of the essence in this thread ...

Actually download of an undamaged recorder can be done using a notebook with an ethernet interface. The EAFR even has an integrated webserver to browse through the recorded data. - At least that\x92s what GE promises.

But has AAIB India ever had to get data directly from the memory chips due to a badly damaged data recorder? I think it would have the capability.

You may be thinking of a Quick Access Recorder (QAR), which is indeed designed to be downloaded in situ. They've been around for a while.

That aside, I think we're agreed that downloading an intact FDR/EAFR is probably several orders of magnitude easier than one that's been burnt, battered or bruised.

I do SMD rework and failure analysis on automotive control devices and if there would be so much at stake, even if I would be a known expert, I would ask for something to 'play with' or in less offending words: test the equipment, process and success rate on something from the 'scrapyard'. Experience would prevent me from starting with the FDR from the flight.
Maybe they officially need a week to decide where to put it while exactly this is happening, they are doing a dry-run.

Sure. I often referred to the zillion-dollar systems I worked with as toys to play with, but only in some contexts and with some listeners. And I would likely be offended by my work in the context of a catastrophic event being referred to as playing. I think most of us might be.

Also, please note that I have no comment on whatever decisions may have been made or be pending, in this accident, about where to download and analyze the data. Well, no comment except that I see no reason to question the Indian authorities' ability to make those decisions appropriately and with adequate knowledge and expertise.

No, no, I was thinking about the FDR data being downloadable from the EAFR through the aircraft's network. Be it with the Maintenance Laptop (which I presume) or any kitchen-grade laptop with a physical ethernet port (which I hope is not the case). But I have no clue on what an appropriate device is for such an operation.

Regarding the QAR, the 787 is or can be equipped with a WQAR, but I hate to type the W, as in Wireless, as the moment I hit the 'enter' button, Starlink interfaces will be devised and engineered on the spot....

One note of QAR data\x97it\x92s transmitted to provide flight data monitoring (.Flight Ops Quality Assurance, in FAA land). The QAR data might help, but it\x92s not transmitted in real time only after block in.