Posts about: "FADEC" [Posts: 194 Pages: 10]

Still FLS with some decent engineering background,

Said so my apologies if is not pertinent to the discussion.

I am puzzled by the TCMA logic, as shown on the patent, which of course could have nothing to do with final design, but clearly in my understanding the two FADEC channels are acting in series, therefore by design they do not need to concur to shut down the engine. Am I wrong?

That is correct, at least if the designed and implemented system did what the patent application said it would do.

In the words of the patent application: Both channels are \x93always actively monitoring engine function and independently have the capability of shutting down the engine.\x94

PanMe: To be fair, if the fault is shown to be from the FADEC, then you can hardly blame Boeing, since both engines and FADEC come from GE.The FADEC presents a command set and interface to whatever controls it, so a possible failure mode could be at that interface, a mismatch and or race condition between the controlling sequence of commands, and the FADEC response to that.

Yet the (a?) patent application for the TCMA addition to the EEC was filed by Boeing.

I guess we'll eventually find out what bits were actually connected to the engines fitted to the accident aircraft, by whom and when.

Lead Balloon: "Yet the (a?) patent application for the TCMA addition to the EEC was filed by Boeing."

That sounds right, since it's an airframe related issue, not specific to the engine.

Your other implied question, ie: Is the TCMA software part of the FADEC , or something Boeing designed and built. Or, where is that functionality resident in the system, and who designed and built it ?. Starting to think that this tragedy may have had a far more subtle cause than has been imagined thus far.

Boeing's patent application says: My understanding is that "EEC" is Boeing for "FADEC".

But I have to reiterate, and as others have noted, that we don't know what actual TCMA systems, if any, were fitted where and how it was wired into the accident aircraft's engines, or whether the specific state of the TCMA systems, if any, were monitored by the flight recorders.

I (and I think everyone else here) have been assuming that the FADEC does in fact have a dedicated permanent-magnet alternator, as is the case on the Airbuses (confirmed by FCOM) and surely the 737.

I have been told elsewhere that this is not the case. A read of the draft FCOM available online for the 777 & 787 makes no mention of a FADEC generator, but then neither does the 737 manuals. Is this simply a case of "Boeing thinks you don't need to know"?

It has been proposed that the primary source of power for the FADECs is actually the flight control PMGs, mounted on the engine gearbox, but that this power goes to the avionics bay, has failover switching gear, and comes back to the EEC.

Can anyone shed concrete light on this (e.g. a source that clearly states there is both an EEC alternator and a flight control PMG on the accessory gearbox)?

Alternator and generator seem to be used interchangeably in this context.

It's not quite that, but there is a list of received channels for a GEnx 787 in the FDR report into one of the original battery fires . Unfortunately, it is only a list of parameters that they used and verified in the investigation - the only ones listed for the engines are N1 and cutoff switch. Other accident/incident FDR reports might be more focused on engines and include a similar table.

I don't think you'll find an actual wire list for it (or it won't be useful) as apparently most/all of the data is via an ARINC bus.

I attempted to PM this but your inbox is full.

[SLF with an electrical background and some exposure to ground-side critical facilities power]

The details don't really matter, but this is the certification requirement:

​​​​​​​ https://www.easa.europa.eu/en/docume...s-engines-cs-e

Once again tdracer confirmed the PMGs for the FADECs in the first AI171 thread. He even explained the logic behind it and the connections with the onboard electronics:
- Each engine has a PMG for the FADECs
- Only for engine start the FADECs are powered by the aircraft
- Once the engines are running, this connection is opened
- It is verified, that the FADECs are then no longer connected to the aircraft electrical system. A failure to open the connection triggers a "No dispatch" message
- In case the PMG fails, the FADECs are once again powered by the aircraft electrical system

Yes. That is what I have read here, that is my assumption, that is how Airbus does it, that is what makes sense .

But I am being told elsewhere by someone with an A&P badge that that is not quite the whole story, and that the FADEC PMGs do double-duty as the flight control PMGs.

I am hoping for some documentation to confirm/refute that.

Somone Somwhere:

"But I am being told elsewhere by someone with an A&P badge that that is not quite the whole story, and that the FADEC PMGs do double-duty as the flight control PMGs."

Is that likely ?. The whole point of the PMG must be to ensure hermeticity of operation of the FADEC, when all else fails. That becomes compromised if the PMG also has a FADEC external load placed on it.

Well, tdracer worked on engine/airframe integration for Boeing. He did that for the GEnx on the B747-8. I would guess he knows more about those systems than some guy with an A&P badge.

That is how it's done on the EC-135 helicopter (also FADEC controlled). One failed engine will disable the overspeed protection for the remaining engine. Of course a helicopter is a whole different story, though.

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.

Actually, according to tdracer , each channel of the FADEC gets just one throttle resolver input, as the two resolvers are on separate wiring looms. So, the FADEC is using the dual channel feature to handle erroneous throttle position inputs. However, according to the patent at least, each channel can trigger TCMA and cut the fuel supply independently. So now we're down to only needing only one erroneous throttle signal per engine. Or one wrong interpretation of a signal, e.g. value clipping where you shouldn't (shortcircuit -> idle), some integer overflow etc.

So, from my understanding, if there is an issue with some of the throttle position sensors, the FADECs will detect a disagreement and keep the high thrust -> assume safe is "fly", whereas one of the TCMA channels might read or misinterpret throttle position close to idle. As the thrust doesn't decrease, at some point the upper bound of the falling TCMA thrust contour will be breached and the engine will be shut down.

A different set of PMGs.

EDLB: Shutdown.

Excellent summary, but could that command have originated via the data bus, as a message sequence to the FADEC ?. If so, where from ?.

Battery power should still result in a controllable aircraft and controllable thrust.

Thrust lever resolvers are powered by the FADECs, so as long as the engine remains running, it will know what requested thrust is from the pilots. You presumably loss A/T.

I certainly expect and hope so. But I can't find any 787 or even 777 documentation confirming it.

Whether the PMA for the FADEC is certified as part of the FADEC... not sure.

On the B777, each EEC is powered by a dedicated control alternator whenever the engines are running. The control alternators are mounted on the forward side of the main gearbox of each engine.

The flight controls power supply assemblies (PSA) have several sources of power, including PMGs located within the backup generators.

The EEC control alternators do NOT perform double duty by powering the flight control system PSAs. I can't imagine the B787 being much different.

Does a Boeing 787 go from HOLD TO/GA to THR REF/VNAV SPD at 400' AGL/AAE, like older versions of the Boeing?

If so, what if the WoW stayed in ground mode, for whatever reason, how would that affect

1) Retraction of the landing gear (it didn't retract, as obvious in videos released)

2) The transition from HOLD to THR/REF at 400' (they reached just barely over 400' AGL before leveling, then descending)

I am also thinking that Air India would follow Boeing procedures in that the left seat pilot will move their right hand away from the thrust levers at V1, and thus, at 400', the thrust levers are not guarded or monitored?

Even if thrust levers were pushed forward, is there some kind of logic related to FMC and-or FADEC or other involved systems, which regardless of thrust lever position commands IDLE thrust to the engine?

Remember that Airbus accident where the aircraft thought it was landing, while the pilots wanted full thrust, and they crashed into a small forest because some kind of idle is all they were afforded by the system?

If the engines of this 787 thought it was in the rollout or final part of the flare, it might also command thrust levers to idle?

This does not explain the RAT, though, unless there is some weird combination of software working against each others logic.

Had the engines failed by some really random, odd reason, like birds, fuel contamination-vapor-starvation or such, wouldn't there be at least a slight bit of roll or yaw visible? Even with TAC or whatever they have on the 787, I would think even a 1 second difference in thrust reduction between the engines, a hint of yaw or roll should be visible ...

Thoughts, especially by someone who flies the 787?