A320 Master Caution attention-getter
 

When the master caution button lights up in yellow, but on one side displaying only CAUT (lower part of the button) and on the other side only MASTER (upper part of the button), without any sound or ECAM warning, what does that mean??

As I remebmer from few years back, it meant something like FWC doesn't function normaly or has some misbehaviour but I cannot find the reference anymore.

Hi Cak,

As you imply, it suggests failure of one of the two FWCs. But if in doubt, check the filaments..

For a single FWC fault you should still get an ECAM warning. For a dual FWC fault you wouldn't see any master caution/warning lights.

Could be a burned out bulb , did you put lights on test to check?
For a single FWC yo should get an ECAM.

I've had this in cruise, no associated ECAMs

It is not burned bulb, I checked and I had it few times before

As I said and Chris Scott also obviously knows about this, it's something with FWC misbehaviour but I don't remember exactly what and there is no reference in FCOM. I think that it's in AMM but I don't have it :)

If I remember corectly, FWC1 is wired to supply Master Warning and Master Caution upper bulbs on CM1 side and lower on CM2 side. FWC2 does the opposite.

I would appreciate a reference

Cak, you remember correct! FWC1 trigger the MASTERs on the left and WARN and CAUT on the right side (FWC 2 the opposite way round)

IFixPlanes - not quite....

AMM 31-00-00
For a more exact description, you have to infer the connections from what's in the Trouble Shooting Manual 31-53-00. The top globe of the Captain's MASTER CAUT is troubleshot with replacement of FWC 1 and for the lower globe replacement of FWC 2. Vice Versa for the CM2 station.

No - quite right!
If you read my posting carefully, you will notice that we write the same thing in different words.
(but i have to admit, that i leave out the word "part")

It's fairly common in my experience. Seems to be associated with electrical transients.