Posts about: "Thread Moderation" [Posts: 120 Pages: 6]

Actually, nobody should "read post #867".

The mods are doing a sterling job removing hundreds of irrelevant posts. I'm not suggesting for a moment that the one you're referring to falls into that category, but it's highly likely that the mods continuing valiant efforts have resulted in the post in question now having a different sequence number.

Much better to use the "permalink" facility - that's why it's there.

It is obvious to the Mod Team that there is an overwhelming amount of posts from PPRuNers new and old who have not read the thread nor used the Search function before bursting into print.

For the sake of our sanity and personal time this thread is closed for a couple of hours to give you all time to actually read it before launching into your version of events.

I haven't managed to read every post in this thread, just a large percentage, so please excuse me if these points have already been raised. I'll post each separately in case the mods deem them irrelevant or redundant, in which case, my humble apologies.

First, the RAT. There has been a lot of discussion about this, and I suspect the audio analysis a few posts above pretty well confirms that the RAT was deployed. However, I don't think the following question has been asked, and I believe it's further weight in support of RAT deployment.

Q: Why does the video of the plane passing at low altitude, (potentially taken from an apartment window or balcony door), even exist?

I have lived near an airport flight path for many years, and would never bother to video a passing plane unless I perceived it was truly exceptional. Normally, I don't even look, unless it sounds off course, very loud or some such reason. I have yet to take such a video. Here, of course, I'm assuming that the video-taker lived in or near the building concerned, and was therefore equally used to the sounds of passing planes. I submit that the video was shot purely because the camera man (by the voice sound, but an assumption - maybe not the camera operator's) recognised that the sound he was hearing was indeed exceptional. The video begins with the plane out of the shot, so he 'must' (assumption) have heard it coming, and had time to get his phone and starting videoing. Of course I'm saying that he was hearing the RAT...

Secondly, I have found that different versions of the same video play differently (on the same hardware). In some, I cannot discern the RAT sound - unless I reduce the playback speed. Then, it seems to be very distinct - but whether this is an artifact of the reduced playback speed, I can't say. I suspect that different playback applications and hardware will also have a major influence on the RAT audibility. I am 100% convinced that the RAT sound was captured, but is not audible to all, for one or more of these reasons.

Oh, lastly, I'm guessing the (AI) RAT frequency in the audio spectrum analysis was probably lower because the plane was travelling slower than in the other, more controlled cases. Equally, the load on the AI RAT could have been greater, for any number of reasons.

B787 skipper again..... Many thanks for your kind comments and PMs about the post previously known as #867. Due to mods weeding of posts it is now HERE .

First catastrophic incident with a 787 (and first with a composite fuselage?) is going to attract significant attention. No immediate apparent cause and multiple lines of largely speculative thought (flaps, RAT, thrust availability etc.); an aircraft manufacturer which has been under intense scrutiny for quality issues including accusations related to the 787; and just to top it off, accusations of poor maintenance/management practices of aircraft by the airline - it all builds up to a moderator's nightmare. Having read a lot of posts that were later removed, I'm impressed that the thread has only been locked the once.

As SLF with non-aviation engineering background, but an interest in aircraft, I offer no theories on what happened, as I haven't got a clue.

Given the quality of the video you cannot see that the RAT is NOT deployed either

Another hour spent sifting through the stuff since last night (my sympathies to the mods ). A few more comments:

"Real time engine monitoring" is typically not 'real time' - it's recorded and sent in periodic bursts. Very unlikely anything was sent from the event aircraft on this flight.

Commanded engine cutoff - the aisle stand fuel switch sends electrical signals to the spar valve and the "High Pressure Shutoff Valve" (HPSOV) in the Fuel Metering Unit, commanding them to open/close using aircraft power. The HPSOV is solenoid controlled, and near instantaneous. The solenoid is of a 'locking' type that needs to be powered both ways (for obvious reasons, you wouldn't want a loss of electrical power to shut down the engine). The fire handle does the same thing, via different electrical paths (i.e. separate wiring).

As I've noted previously, a complete loss of aircraft electrical power would not cause the engines to flameout (or even lose meaningful thrust) during takeoff. In the takeoff altitude envelope, 'suction feed' (I think Airbus calls it 'gravity feed') is more than sufficient to supply the engine driven fuel pumps. It's only when you get up to ~20k ft. that suction feed can become an issue - and this event happened near sea level.

Not matter what's happening on the aircraft side - pushing the thrust levers to the forward stop will give you (at least) rated takeoff power since the only thing required from the aircraft is fuel and thrust lever position (and the thrust lever position resolver is powered by the FADEC).

The TCMA logic is designed and scrubbed so as to be quite robust - flight test data of the engine response to throttle slams is reviewed to insure there is adequate margin between the TCMA limits and the actual engine responses to prevent improper TCMA activation. Again, never say never, but a whole lot would have had to go wrong in the TCMA logic for it to have activated on this flight.

Now, if I assume the speculation that the RAT deployed is correct, I keep coming up with two potential scenarios that could explain what's known regarding this accident:
1) TCMA activation shutdown the engines
or
2) The fuel cutoff switches were activated.
I literally can come up with no other plausible scenarios.

In all due respect to all the pilots on this forum, I really hope it wasn't TCMA. It wouldn't be the first time a mandated 'safety system' has caused an accident (it wouldn't just be Boeing and GE - TCMA was forced by the FAA and EASA to prevent a scenario that had never caused a fatal accident) - and there would be a lot embarrassing questions for all involved. But I personally know many of the people who created, validated, and certified the GEnx-1B TCMA logic - and can't imagine what they would be going through if they missed something (coincidentally, one of them was at my birthday party last weekend and inevitably we ended up talking about what we used to do at Boeing (he's also retired)). Worse, similar TCMA logic is on the GEnx-2B (747-8) - which I was personally responsible for certifying - as well as the GE90-115B and the 737 MAX Leap engine - the consequences of that logic causing this accident would be massive.

A TCMA bug just doesn't bear thinking about, I really hope that doesn't turn out to be the case.

Firstly, I've read through this whole thread - thank you Admin & Mods for your considerable efforts to clean things up.

Secondly, as a (now ex) glider pilot who remains extremely interested in aviation in most of its forms, this discussion has been an education and thought-provoking, as it so frequently is whenever I lurk here (usually without logging in). Thank you all for sharing your knowledge, expertise and thoughts.

To my mind the above post (especially the sentence I highlighted) is amongst the best (and most succinct) summary of what the pilots likely faced, with little to no time to resolve the situation. I cannot imagine those last few seconds and my heart goes out to them, the passengers and the many loved ones left behind. If there is any good that can come of this, it is that the cause is found quickly, with no bias, and steps are taken to ensure the same holes in the cheese cannot happen again.

Hello posters,

We mods are working away on this thread. To be honest, I cannot recall a recent thread with more discussion - which is what we're we for! Good!

That said, I, and several other mods, have asked that posters "familiarize themselves" with the contents of the thread. Maybe read all of it, maybe read back a few days before posting. Has what you're thining to post as "new" information, already been presented and discussed (and perhaps dispositioned)? We mods have read most of the posts, so we're trying to stay on top of it, to give readers less to no nonsense to have to read through. We have asked some respects for the crew, particularly in regard of postulated intentional acts - just don't.... unless firm, credible (future) evidence opens this theme. We mods are clearing out such posts with no mercy, but it's still work, and other decent thoughts may get lost in the dustbin as a result (we very, very rarely edit out only a part of a post).

And yes, report posts which you really feel are not worthy here, we mods do consider every report. That said, how about not making report worthy posts! My [our] inboxes have been filled with report emails this time around.

We eagerly promote good compliant [to PPRuNe rules] discussion, keeping posts within the guidelines makes it more enjoyable for everyone, and less work for your mod team - we really are trying to keep this place the professional pilot discussion you're looking for!

Thanks, Pilot DAR

P.S. Please don't post AI generated crap, okay? (thanks for reminding me Tu.114)

Thank you for your efforts mods - don't envy your task on this thread (from a simple long time lurker first time poster in this thread SLF!).

Keeping track of this thread is tiring - again, my sympathies to the mods, as tiring as I find it, it must be far worse for them )
Apologies for a few terse posts last night, but a couple of inane posts (by a usual suspect) really set me off. I've never used the 'ignore' function, but I may need to revisit that.

I posted this previously, but it was about 70 pages ago, so I understand not going back that far, or forgetting that tidbit amongst all the noise.
In short, I'm not familiar with the specific air/ground logic on the 787/GEnx-1B - the logic I posted (3 radio altimeters, 2 Weight on Wheels, at least one of each must indicate 'on-ground) is for the 747-8 (which I'm intimately familiar with). I have a vague recollection of a discussion with my GEnx-1B counterpart 10 or more years ago that suggested that the 787 was not as complex as the 747-8, but I don't recall any details. Basic FADEC logic (BTW, as someone else noted - it's "Full Authority", not "Autonomous") is to default to 'air' if in doubt, as it's considered to be 'safer'.
The only real hardware in the TCMA system is the N2 overspeed shutdown system - which goes through a BITE style functional test on every engine start. Everything else is in software - with the only aircraft inputs being Air/Ground and thrust lever position.

As I've posted previously, the FADEC is powered by a dedicated Permanant Magnet Alternator (PMA) - aircraft power is used only as a backup for starting or if the PMA fails. If the FADEC determines it is running on aircraft power with engine running (i.e. the PMA has failed), it sets a 'No Dispatch" fault message.

Okay posters,

I just deleted a stream of posts relating to a "report". There were enough errors to make that "report" very suspect to me (and I trust tdracer's instincts - so I've left his post with the quotes - for the humour).

Please, for all our sakes, and the sanity of the moderating team, do not post things which could appear authoritative, unless you are prepared to attest to their authenticity, and identify the source. Sure, real information is going to come out, please, please do not dilute it's value to all of us by posting nonsense which confuses the real information.

We mods will confer about this, though I fear we may need to begin some thread locks while information becomes authentic, and we confirm it, before allowing the AI nonsense to pollute it!

There was a comment very early in the thread (couldn't locate just now so assume hoovered up by the hard-working Mods) where someone postulated that the late "flare" we see in the video was possibly a pitch-up moment as the engines relit and the pilots went from a glide to a climb posture.

I don't want to review the video again -- personally, I suspect the "revving" the survivor heard was the sound of the RAT spooling up, and that the pilots were flaring as the ground approached in the vain hope of setting her down gently. Just sharing the OPs suggestion as it relates to your comment

I was not aware that we have granular ADS-B data from the a/c itself showing airspeed post rotation (rather than speed interpolated from GPS). Apologies if I have missed it. If it does show acceleration after takeoff I tend to agree with you.

In no particular order, here are some more thoughts on TCMA having caught up on the thread:

If you cut the fuel from two big engines at take-off power, there must be some delay before n2 decays below the threshold for generation (below idle n2), the generators disconnect and RAT deploys. GEnx have relatively long spool up/down times as the fan is so large (and would be exposed to 170+kts of ram air). Perhaps someone has a view on how long this would be, but I imagine it could easily be 10s or more between fuel cut off and RAT deployment. On AI171 the RAT appears to be already deployed at the beginning of the bystander video. That starts c. 13s before impact and around 17s after rotation. This does not prove anything except that the supposed shut down must have happened very close to rotation and could have happened just before rotation while the a/c was on the ground.

As a thought experiment, imagine if ANA985 in 2019 had decided to go around. The a/c rotates and is ~50 ft above the runway, suddenly both engines spooling down, very little runway left to land on and no reverse thrust available. I am struck by how similar this scenario is to AI171. This theory would require there to have been unexpected thrust lever movement in the moments before rotation - but plausibly one pilot moving to reject, followed by an overrule or change of heart - or even a simple human error such as the recent BA incident at LGW - could achieve this. This is perhaps more likely that any sensor fault that you would expect to only impact a single engine given the redundancy of systems.

Tdracer writes that a key requirement of TCMA is to identify an engine runaway in the event of an RTO, in order to allow the a/c to stop on the runway. This will have been tested extensively - it is a big leap to imagine a false activation could be triggered. It did happen on ANA985 but through a very unusual set of inputs including application of reverse (albeit this latter point may not be relevant if TCMA logic does not distinguish between the reverser being deployed or not).

Incidentally there is an assumption the TCMA software version in place on the ANA flight had already been patched and fixed on AI171. That probably is the case but I am not sure it is a known fact.

In summary I remain baffled by this tragic accident. I have not yet read anything that explicitly rules out TCMA activation and it remains a possibility due to the vanishingly small number of factors that could shut down two engines at apparently the exact same moment when they have fully redundant systems. Fuel contamination, for example, has typically impacted each engine a few minutes (at least) apart. I am also cautious (as others have pointed out) of a form of confirmation bias about Boeing software systems with four-letter acronyms.

In my mind the cause could equally well be something completely different to anything suggested on this thread, that will only become clear with more evidence. All of the above also incorporates a number of theories, i.e. that there was an engine shutdown - that are not conclusively known.

Thank you to the mods for an excellent job.

Again, this thread has become a Hamsterwheel of repetition and guesswork mixed in with nuggets of information and professionalism.

Until we have the time and ability to sort out which is which it will be closed.

Another hour spent sifting through the stuff since last night (my sympathies to the mods ). A few more comments:

"Real time engine monitoring" is typically not 'real time' - it's recorded and sent in periodic bursts. Very unlikely anything was sent from the event aircraft on this flight.

Commanded engine cutoff - the aisle stand fuel switch sends electrical signals to the spar valve and the "High Pressure Shutoff Valve" (HPSOV) in the Fuel Metering Unit, commanding them to open/close using aircraft power. The HPSOV is solenoid controlled, and near instantaneous. The solenoid is of a 'locking' type that needs to be powered both ways (for obvious reasons, you wouldn't want a loss of electrical power to shut down the engine). The fire handle does the same thing, via different electrical paths (i.e. separate wiring).

As I've noted previously, a complete loss of aircraft electrical power would not cause the engines to flameout (or even lose meaningful thrust) during takeoff. In the takeoff altitude envelope, 'suction feed' (I think Airbus calls it 'gravity feed') is more than sufficient to supply the engine driven fuel pumps. It's only when you get up to ~20k ft. that suction feed can become an issue - and this event happened near sea level.

Not matter what's happening on the aircraft side - pushing the thrust levers to the forward stop will give you (at least) rated takeoff power since the only thing required from the aircraft is fuel and thrust lever position (and the thrust lever position resolver is powered by the FADEC).

The TCMA logic is designed and scrubbed so as to be quite robust - flight test data of the engine response to throttle slams is reviewed to insure there is adequate margin between the TCMA limits and the actual engine responses to prevent improper TCMA activation. Again, never say never, but a whole lot would have had to go wrong in the TCMA logic for it to have activated on this flight.

Now, if I assume the speculation that the RAT deployed is correct, I keep coming up with two potential scenarios that could explain what's known regarding this accident:
1) TCMA activation shutdown the engines
or
2) The fuel cutoff switches were activated.
I literally can come up with no other plausible scenarios.

In all due respect to all the pilots on this forum, I really hope it wasn't TCMA. It wouldn't be the first time a mandated 'safety system' has caused an accident (it wouldn't just be Boeing and GE - TCMA was forced by the FAA and EASA to prevent a scenario that had never caused a fatal accident) - and there would be a lot embarrassing questions for all involved. But I personally know many of the people who created, validated, and certified the GEnx-1B TCMA logic - and can't imagine what they would be going through if they missed something (coincidentally, one of them was at my birthday party last weekend and inevitably we ended up talking about what we used to do at Boeing (he's also retired)). Worse, similar TCMA logic is on the GEnx-2B (747-8) - which I was personally responsible for certifying - as well as the GE90-115B and the 737 MAX Leap engine - the consequences of that logic causing this accident would be massive.

Keeping track of this thread is tiring - again, my sympathies to the mods, as tiring as I find it, it must be far worse for them )
Apologies for a few terse posts last night, but a couple of inane posts (by a usual suspect) really set me off. I've never used the 'ignore' function, but I may need to revisit that.

I posted this previously, but it was about 70 pages ago, so I understand not going back that far, or forgetting that tidbit amongst all the noise.
In short, I'm not familiar with the specific air/ground logic on the 787/GEnx-1B - the logic I posted (3 radio altimeters, 2 Weight on Wheels, at least one of each must indicate 'on-ground) is for the 747-8 (which I'm intimately familiar with). I have a vague recollection of a discussion with my GEnx-1B counterpart 10 or more years ago that suggested that the 787 was not as complex as the 747-8, but I don't recall any details. Basic FADEC logic (BTW, as someone else noted - it's "Full Authority", not "Autonomous") is to default to 'air' if in doubt, as it's considered to be 'safer'.
The only real hardware in the TCMA system is the N2 overspeed shutdown system - which goes through a BITE style functional test on every engine start. Everything else is in software - with the only aircraft inputs being Air/Ground and thrust lever position.

As I've posted previously, the FADEC is powered by a dedicated Permanant Magnet Alternator (PMA) - aircraft power is used only as a backup for starting or if the PMA fails. If the FADEC determines it is running on aircraft power with engine running (i.e. the PMA has failed), it sets a 'No Dispatch" fault message.

And this just highlights the difficult decision faced by moderators when trying to reduce noise on a thread because, without this additional supporting information , I too raised an eyebrow over the claim of hearing hundreds of RAT deployments.

NOT especially getting at you slacktide , indeed thanks for the followup and presenting your experience/reasoning, however, to assist everyone, including *relevant* background/support detail with one's post is to be encouraged! If you don't have this, or are just speculating from a position of little experience or knowledge, maybe the best contribution would be to sit on your hands for a bit and learn from others?

FP.

B787 skipper again..... Many thanks for your kind comments and PMs about the post previously known as #867. Due to mods weeding of posts it is now HERE