On my Socata TB20’s right side panel there is an on/off switch labeled as EPU.
I don’t know it’s function and the previous owner doesn’t remember what is it for.
Would it be possible to be a switch for an emergency power unit, maybe a backup battery for the Sandel 3308 EHSI? Turning it on or off doesn’t seem to do anything and I keep it closed for now, before I’ll have a chance to check all the wires behind the panel…
It might be a backup vacuum pump. You should be able to see it under the cowling, if fitted. It’s a fairly big and heavy thing. Very few people use them.
