Posts by user "EDLB" [Posts: 12 Total up-votes: 0 Pages: 1]

Long story short. Something or someone disrupted the fuel supply on both engines simultaneously around rotation time. In a way that a line check captain could not correct it in 10+ seconds remaining flight time. Occam razor at this stage would say, that both fire handles were activated. Hope that the investigation comes up with something different.

We have two donks individual fuel supply cut simultaneous in split seconds. There is no rudder activity visible for any thrust asymmetry during this timeframe. TCMA is implemented via the FADECs which are independent for each engine with their own power source from each engine. TCMA is designed to shut down its engine if its power lever is in retard position and the engine is still powering with too much thrust. In addition the airplanes ground sensors must indicate that it is on the ground. For each thrust leaver there are two independent position sensors. It is similar redundant designed as in modern car acceleration pedals. A dual redundancy in each thrust leaver. For TCMA to shut down two fuel supplies within split seconds we have to assume that 4 thrust leaver sensors malfunctioned and the ground sensing logic failed at the same time. The probability that this happens is nil (may be 1 in every 10exp15 hours) which would be about 10 times the age of our universe.
Unless there is a software error in the FADEC TCMA system which only came to light on this flight. But there seem to be nothing special on this flight until rotation. If there is a software error I expect, that we get false single engine shut downs first. And that would already made the news if it happened during rotation.

FADEC Power supply: The Safran FADEC used on the GEnx-1B here is most likely a Generation 3 FADEC. The same Generation as used for CFM56-5 and -7 in A320 etc. So with high probability the same overall topology with independent 3 Phase alternator supply for the FADEC is used because similar certification standards are required and nobody develops a FADEC from scratch if he has a proven and qualified one.
Detail form Airbus here: https://studylib.net/doc/27601211/51...british-cfm-56

Safran FADEC Gen 3 uses: https://www.safran-group.com/product...engine-control

- CFM56-5B de CFM International

- CFM56-7B de CFM International

- CF6-80C2L1F de General Electric

- CF6-80C2K1F de General Electric

- GE90-115B de General Electric

- GEnx-1B de General Electric

- GEnx-2B de General Electric

- GP7200 d’Engine Alliance

- TP400-D6 d’Europrop International.

So if there is a latent failure in the design or software of this FADEC generation which can lead to a dual EFATO most of the current airliners worldwide have to be grounded.

Software issues: Keep in mind that the FADECs come (and go) with the engines. On a 11 year heavy used 787 you will have different engines, changed several times on each side with much different age engines and FADECs. Most likely on different software stages. When two different engines likely several years apart in the making stop at the same second it must have a common cause.

@syseng68k
Consensus here is, that both engines where stopped by a closing fuel cut off valve, wich yields a fast loss of N2. The generators then shut down very quick as does the thrust in a few seconds. This is supported by the quick RAT extension which allowed the crew to control the flight. The APU did autostart too. A thrust changed with the thrust leaver to idle is much slower and would not result in the dramatic change in performance. Thrust set to idle will not engage the RAT since the electric generators would still work. So a thrust leaver changed to idle or any intervention by Autothrust (AT) would not yield to the RAT extension. Something or someone activated a fuel cut off. How and why that happened is the big question, the investigators have to answer.

Thanks. The mostly intact aft recorder has only data until the engines lost power. Only the forward recorder has 10 minutes additional due to his own internal battery backup. This might explain, why a recorder is sent to Washington DC. It is most likely the much damaged forward recorder, which hopefully holds data after the engines lost power.

Some assumed numbers about normal biotreatment.
https://www.biobor.com/wp-content/up...ation-IATA.pdf

If we assume 50 tonnes fuel load a 100ppmw biotreatment will be 5kg of biocide total in all tanks.

The GEnx-1B will burn about 4,5kg/s fuel each on a take off run (give or take a bit) so 9kg/s in both donks for about 20s until rotate.

So the total nominal biocide dose could be pumped in about half a second through both engines on take off power if it where not mixed at all and arrives in both engines at the same time.

This gives you an idea that with the nominal amount of biocide dose not much could have happened. If biocide is the source of this dual EFATO than an extreme overdose in addition to wrong application preventing mixture with the fuel had to be the case.

If someone is interested how much detail in the EFARs is stored the 2013 B787 Japan Airline battery incident is a good example. https://data.ntsb.gov/Docket/Documen...man-Master.PDF

Given the wealth of data and the 10 minutes RIPS supply for the forward EFAR the investigation body should by now have a good idea how the events unfold.

Leaking lavs are a matter of poor design, as in a nuclear power plant you can design piping to be robust and failure proof. The US home installation and piping is on the low end of engineering and quality, so that should not be the reference point. However if water ingress was involved it is only a matter of engineering and commercial will to make that bullet proof in an airliner. Looking with German eyes through an US Home Depot was always some fun for an engineer.
If you are stuck with the location then improve the quality. If a 10th of the engineering involved in a new furbo fan jet engine goes into a lav...

From the link above:
The minister called the crash a "rare case". "It has never happened that both engines have shut down together," he said

So they have no clue even with both recorders read out, why both engines shut down at the same time.

Sabotage on the electrical fuels shut down:
Would require detailed knowledge about the wire routing, which is independent for both engine sides, so any "device" would be difficult to get into the electric harness. I would rule that out, unless they find foreign devices wired in on the wreck, because there are way simpler methods to get an airliner down.

Fuel contamination:
There is no smoke, no puff, nothing visible on the exhaust. Both engines went from clean burning to immediate shut down at the same time within less than a second. I think that is close to impossible with any method of fuel contamination you can come up with. There ist always some mixture you would burn and the less perfect burn rate would show as smoke. At take off you have something around 5kg per second fuel burn rate per engine, so you have to come up with non combustible "fuel" in this rate on the exact time on both engines.
Highly improbable.

I find it very disconcerting that with downloaded recorders the investigators seem to have no clue how and why the dual engine shut down happened. How can they be sure that this unrecoverable problem was/is limited to the AI171 flight.

Yes positively. In the doc I posted above page 16
https://data.ntsb.gov/Docket/Documen...man-Master.PDF

Eng1_Fuel_cutoff
Eng2_Fuel_cutoff

You get a good impression about the overwhelming wealth of parameters.

The report proved that occams razor was right. Fuel switches acted which was the simplest explanation. And occams razor will not allow for a 15000h line check captain as PM to need over 10 seconds to reset fuel switches while both engines spooled down from TO thrust to sub idle within 5 seconds.