Flap Control Units (FCUs)

[Hardy Heinlin]

In this circuitry quoted below, if you look at the upper left quarter you will see a box for RVDT excitation signal processing, with wires leading from and to the FCU box:

Here's a compilation of diagrams... The signal path from the inboard TE flap position sensors is not quite clear. There is also a labelling anomaly on one diagram.

High Idle Circuitry (GE)

OK, I see your theory. You are saying all FCUs provide power to all RVDTs, and all RVDTs provide signals to all FCUs.

But why does a certain RVDT fail when a certain power supply fails? The RVDT should still get power from the other FCUs then. But it doesn't (on the real deck).


Edit:

Now I finally-really-absolutely see: On that drawing I missed those little extra wires coming from 1L, 1R, 2R -- they join the wires to the RVDTs outside the FCU box.

[Hardy Heinlin]

I just changed it back to the old version.

Also, I want to change the non-severe FCU malfunction:
All three flap lever RVDTs fail. FCUs still provide flap position data.

This is modeled in the Thales sim as well. They just call it a failure of the flap lever RVDT (singular); they certainly mean a triple failure. And the chance of getting a triple failure is nearly impossible, but ... anyway.


|-|ardy

[Hardy Heinlin]

FCE to FCU Power

This looks like every FCU gets AC power from all four FCEs. When all fails you will get three status messages:

FLAP CONTROL L
FLAP CONTROL C
FLAP CONTROL R

No problem. But when just a certain FCE fails, PSX will show these messages (like on the real deck, I think):

FLAP CONTROL L  >> if 1L and 2L fails
FLAP CONTROL C  >> if 1R fails
FLAP CONTROL R  >> if 2R fails

What does that mean?

a) Status message appears when AC power redundancy is reduced (FCU may still operate)
b) Status message appears when FCU is inoperative, and the diagram shows too much redundancy (an FCU is not powered by all four FCEs)


|-|ardy



Another question:

Is it true that the EIU shouldn't get LE position information when all three FCUs are inoperative while any FCE still provides power to the LE RVDTs?

[John H Watson]

This looks like every FCU gets AC power from all four FCEs.

As far as I can see, the 26Vac power is just to let the FCU know that there is power going to the RVDTs. i.e. for fault reporting, not to power anything in the FCU. The FCEs supply vital DC 15 and 5 volt power to the processing circuits in the FCUs (including power for the ARINC databus transmitters to get data to the EICAS displays and other boxes).

When all fails you will get three status messages:

FLAP CONTROL L
FLAP CONTROL C
FLAP CONTROL R

Do you mean when all FCE's fail.. or all FCU's?

No problem. But when just a certain FCE fails, PSX will show these messages (like on the real deck, I think):

FLAP CONTROL L  >> if 1L and 2L fails
FLAP CONTROL C  >> if 1R fails
FLAP CONTROL R  >> if 2R fails

What does that mean?

Dead FCE's kill the associated FCU completely: DC power is removed from the FCUs (and the minor 26Vac for RVDT "monitoring" inside the FCU). Specific RVDTs are also depowered by specific FCE failure (or FCE pair in the case of 1L and 2L). The DC power generated by an FCEs does not go to all FCUs.

Sorry,  I can't remember the messages generated.

Cheers
JHW

[Hardy Heinlin]

I mean: "When all fails you will get three status messages:"

And: "But when just a certain FCE fails"

Anyway, it's clear now. The extra input is just for fault monitoring. Thanks!

[Avi]

Hi Hardy,

First of all I need to say that the good old times where and when I could response quickly are over. I saw your response and understood you misunderstood me but didn't have the time to explain what I meant.

Now, you basically changed this malfunction back to the way it was in version 10.0.0 with minor modification and I wonder about it:

How do define the total failure of the flaps lever RVDTs? I mean, I understand it is not a power failure but do the FCUs detect this failure?

In 10.0.0 they did and we got the FLAP CONTROL cation message when we moved the lever (without any flaps response). In this version the FCUs don't and we don't get any message, we "get" only the fact that nothing moves and the pilots need to notice it.
Is this how you want it?

Cheers,

[Hardy Heinlin]

Hi Avi,

yes, that's my intention. It's nearly impossible that such failures occur in real life. But the sims contain them anyway for training.


Good luck :-)

|-|ardy


P.S.: You're right. In the Thales sim, for the lever RVDT failure, the FLAP CONTROL caution message will be displayed. I'll add that again.

[Avi]

 

[Jeroen Hoppenbrouwers]

I suppose that only a mechanical rotational disconnect between the flap lever and the RVDT would cause no warning at all. It depends on the construction whether it is possible to mis-rig the mechanism or forget to insert a link pin.


Hoppie