Posts about: "Generators/Alternators" [Posts: 145 Pages: 8]

There is at least one thing common to the TCMA on each engine: The TCMA software.

My recollection may be inaccurate, but wasn't there something in the software for 787 generator control units that would cause generator shut down if the aircraft was 'powered up' for a continuous 248 days? Same software, so all 4 generators would shut down. Is my recollection inaccurate?

What we do know, for sure, is that the TCMAs have the same 'authority' and effect as the fuel cut-off switches. The difference is that the crew control the latter.

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.

I'm pretty sure the software is written independently. Same as Airbus, you don't want the same software error on duplicate critical systems.

Are you saying that the RAT cannot power retraction of the gear, neither via its own hydraulic pump nor via its generator providing power to the centre system pumps?

Or could it be that it's capable of delivering enough power (via either route) to move the tilt actuator but not a humungous retraction jack?

The RAT provides hydraulic power only to the flight control portion of the C hydraulics. Wing and tail flight controls only. Non return valves prevent power to other C hydraulic powered systems like the gear.

The RAT provides electrical power only to critical flight instrumentation (mostly Captains), navigation and communication. The same critical equipment that the Battery will provide. If all electrics was lost, the main Battery would provides standby power until RAT is fully deployed. The RAT electrical power would not be able to power C hydraulic electric pumps.

Yes. Other aircraft systems get the information through the FADECs (including the DFDRs) but the FADECs itself are isolated including independent alternators (PMG). There are two FADECs per engine and each has it's own throttle position sensor. That was explained by tdracer at some point in the old thread.

Should we talk about the RAT being an electrical generator? No? Okay then, carry on.

Did you not read my full post?

The post from which you quoted part did talk about both hydraulic and electrical power from the RAT. I'm not sure what point you're making.

It\x92s happened more than once. I wouldn\x92t foreclose that outcome until we have facts.

The 787 RAT has both a generator and a hydraulic pump.

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

The emergency power system of the 787 surely consists of a lot more than just the RAT. The Reuters article, in its body, uses the term "emergency power generator". Now that could indeed refer to the RAT.

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.

It could equally refer to the APU which some have suggested either started or was in the process of starting.

Yes, but it's clear from context that the WSJ story is referring to the RAT and whatever they may understand from their sources is connected to it.

The story is paywalled, so the link that pops up for me may not work for you, but in case it does:

https://www.wsj.com/business/airline...QPg1BBGQ%3D%3D

I am a software engineer, I find it alarming that the power control unit had the ability to command all AC generator control units to effectively shut down - regardless of that being the side-effect of a bug, or an ability of the system to call on in appropriate scenarios.

Integer overflow is a specific type of issue common to many systems, but like you said - it is something that should be found with robust QA and analysis. The ability to shut down all generators at once from a single source seems like a risky design decision to me and I agree with your point about different software on 2 or more redundant sub systems.

My theory is that this was an accepted risk because the engine-driven fuel pumps would be more than enough in most phases of flight to keep the engines running, and you would still have 2 engines for redundancy. The APU would also restore AC power in lets say 30 seconds and you would then have electric fuel pumps as well.

I think there are several factors that could explain how loss of all AC power during takeoff could lead to a crash:

• The crash happened within 30 seconds - possibly too short for the APU to start, and the RAT doesn't power the AC electric fuel pumps
• The engine driven fuel pumps even if sufficient in level flight may have struggled during rotation - has Boeing tested an actual takeoff with only EDP feeding the engine while the fuel tanks are rotating and in extreme environments, or, have they only tested this statically?
• The takeoff was hot and heavy - combined with the landing gear stuck down and reduced thrust from loss of electric fuel pumps could this be enough?

Perhaps two things might have exacerbated any electrical problems:

1) Electrical Grounding

Boeing whistleblower, Sam Salehpour claims that Boeing used improper techniques to ground electrical systems on the 787, which could lead to arcing, overheating, and potential fire hazards.

2) B787-9 RAT Certification

During B787-9 flight testing, The generator control unit in the RAT experienced a failure during flight testing. This failure led to a delay in the 787-9's certification, as the FAA needed to ensure the reliability and safety of the RAT system.

Based on my previous speculation regarding a BTB short, I wonder how aircraft engines might react in a situation where initially a transient power fault is followed by only battery power being available? As I understand it, there are no longer cable connections to the engines, given no valid inputs from the.thrust levers, what thrust mode would the FADEC's revert to?