In addition, if the Pilot happens to be using ATC1 in a twin Garmin 430 fit, typical of UK Police-fit aircraft,
that will also drop offline when both Gens are lost (as would happen when engines are chopped).
In a fraught situation, he's unlikely to be able to do anything other than press the button & transmit - transmission goes out, or not, through whichever radio was last selected. With a double engine failure, it may or may not be ATC2.
Confused by the reference to ATC1 and ATC2? Transponder? Which is what these CB's are on a 135. Most only have ATC2 with one transponder.
IF you lose SHED BUS and subsequently Avionics Shed you will NOT lose either of your Garmins or your Transponder for that matter (ATC2).
These are on the AVIONICS ESSENTIAL BUS.
Avionic Shed Bus 1 & 2 will have the likes of ANR, TAC, GSM, RAD ALT, MKR, DME etc etc.
Simple Test - walk out to your EC135 - BAT ON - Avionic Master 1 & 2 ON.
Tell us what you see because that is what you will get.
