A320, unusual Master caution

[aurel90]

Hi guys,

Today I had a funny thing on Airbus, let me explain :

During landing (manual one, during flare to be more precise) a Master Caution aural waring rang, the master caution push-button on the Captain side was only showing "MASTER" illuminated (upper line of the pb) and the F/O one was only showing "CAUT" illuminated (lower line), no ECAM, no status, but those lights stayed illuminated until one of us pressed on it.

It's the first time I see this configuration (lights were tested), my captain told me that he saw this case in a CBT saying that it comes from a FWC or SDAC problem. He wasn't sure so we both looked in FCOM, MEL, FCTM and nothing was found :ugh:.

Does anyone of you experienced this kind of thing before ? any idea of what it is ? references ?

Any relative infos would very appreciate :ok:, thanks a lot.

[compressor stall]

FWC fault I'd say.

They are wired so that one FWC illuminates MASTER on one side and CAUTION on the other. The other FWC does the opposite.

Although it could be the sdac if it's amber.

I hope you wrote it up as it will help the cone heads track it down.

[FLEXPWR]

SDAC gathers data mostly for amber (caution) and FWC for most red (warning). However the FWC is directly supplying signal to the lights in the MW & MC pushbuttons.

The FWC1 sends signal to Captain's MW/MC pushbuttons upper bulbs (i.e. "Master" in the MW and "Master" in the MC), but also sends signal to FO's pushbttons lower bulbs ("Warn" in MW and "Caut" in MC).

The FWC does the opposite.

All you need is a power transient or a bus bar power supply change to freeze a FWC (happens regularly during engine starts or APU coming on/offline, especially with the early MSNs). In the case of FWC1, this would be the ESS BUS (CB could be reset -- on ground-- on the OVHD panel).

[aurel90]

Thanks for your quick answers chaps, I think you're both right.

The FWC1 sends signal to Captain's MW/MC pushbuttons upper bulbs (i.e. "Master" in the MW and "Master" in the MC), but also sends signal to FO's pushbttons lower bulbs ("Warn" in MW and "Caut" in MC).

The FWC does the opposite.

Where can I find this information in an Airbus documentation please ?

[compressor stall]

It'll be in the AMM. Not a pilot friendly document, but there's some good descriptive info in there.

Ask your engineering department. If they are not friendly, I did come across a pdf copy online somewhere, but forget where. I didn't download it as I have my own company's.

[flyingins]

Perhaps the PF selected reverse thrust a few moments before the 'weight-on-wheels' microswitch changed from flight to ground? If so there can be insufficient time for the ECAM to illuminate before the conditions for the caution are no longer met and the result can be either an abbreviated Single Chime, an odd Master Caution p/b illumination (such as you describe), or both.

There is no danger if this early reverse thrust selection is inadvertently made (hence it is only a Master Caution and not a Master Warning), but I see it happen on occasion and have caused it myself.

Usually it occurs when pilots are "trigger happy" (gusty, bumpy conditions or when landing on short runways) and want to get the aircraft down and stopped quickly, or when pilots manage to really 'grease' it on. Such a good landing even the aircraft is confused!

I can't explain the precise reason why it occurs but after many years of flying the beasties I have just put in the "it's just an Airbus thing" basket!

[Uplinker]

Flyingins, I agree.

I've done this myself whilst trying to use the partial spoiler function to nail a landing in very gusty conditions, but have got the timing wrong.

I guess the aircraft is telling you that you've selected reverse while still airborne?

[FLEXPWR]

The information is indeed in the AMM.

I wanted to attach some pictures I have from the WDM (wiring) but the pictures are not allowed in this thread, for whatever reason.

Let's try this and see if it works:

Left Frame: https://drive.google.com/file/d/0B4q3MzIVNDC3NEpCUVUzd2dBVTQ/edit?usp=sharing

Right Frame: https://drive.google.com/file/d/0B4q3MzIVNDC3MzN6QmpDN3NZbjQ/edit?usp=sharing

This is a single image split in two for proper fitting on the screen.

[EDA]

The same thing will happen if you "punch" or "stab" the master caution push button quickly. It stays illuminated with master on one side and caution on the other... (at least on our airplanes...).

[nitpicker330]

And sometimes you get an A/T disconnect warning on touchdown as well.