This is related to the problem here:

http://www.captainsim.org/yabb2/YaBB.pl?num=1267554029

I have this 100% on every flight--reinstalling does not help. Some people have reported assigning a key to "avionics master" and cycling that has helped. That didn't help me, but hitting ctrl-e when I lose the radios/etc. worked. What happens after hitting ctl-e is that all my gauges go totally nuts for about 15 seconds, then settle down and I have radios again. Worth a try, anyway.

On the customer support KB captainsim says they're aware of the issue and it's planned for fixing in the next patch. I think that reply has been there for over a year...