VHF Communications systems on aircraft

[qwertyu7]

Homework Statement

Does anyone know why number 1 VHF communications system powered from 28Vdc Battery Bus or 28Vdc Essential Bus and not from another source such as 28Vdc Main Bus or similar power source.

Homework Equations

The Attempt at a Solution

I was struggling to find reasons as to why this maybe so, but i was thinking that it may be because if they do operate on the 28Vdc Essential Bus, they can operate on standby power in case of emergency?

 

[Filip Larsen]

First, I believe radio communication is considered essential equipment, at least on aircrafts that are rated for instrument flying (IFR). Like you said, its not good to loose communication as well if you have engine stop on a single-engine aircraft, for instance.

Secondly, since the main bus is typically is driven by generator that are powered by the engines or APU there is, for larger aircrafts at least, a procedural reason to power the radio stack from the battery so that ground ATC communications can be established before engine or APU start-up.