By Tomas Hansson 840812
#522092 Are your avionics on? Did you check with a default aircraft? It could be that any add-on aircraft that you have, changed from 4.1 to 4.2. What I have done in my sim when I ran into this similar issue is to map the master avionics switch (that may not exist in the actual aircraft) to a keyboard shortcut (shift-a) and used that to "enable" the radios.
By Tomas Hansson 840812
#522095 Just because your aircraft thinks that the avionics are on, it doesn't necessarily mean that P3D agrees! I would strongly recommend that you use a shortcut to turn on the "internal" master avionics as well. Let us know how it goes with a default aircraft...
By Ross Carlson 887155
#522096 I use ProSim737 as well, but I haven't yet moved to p3d 4.2 since I saw some people in the ProSim forums talking about problems with 4.2. Have you searched the ProSim forums for issues with 4.2? I think one of them had to do with a change from 2 decimal places to 3, in the radios. Might be related.
By Tomas Hansson 840812
Vernon Howells 1322809 wrote:Its not working again. I don’t know why

Can you maybe be more specific? Is it now not working in the default aircraft? I think we already determined that this issue seems to be specific to ProSim737 in P3D v4.2. Did you follow my recommendation above?
By Ian Niblo 823150
#522176 I seem to remember that this is all tied to the Avionics Master switch which doesn't exist in the 737. Fortunately you can use FSUIPC to toggle the hidden Avionics Master Switch offset so at least you can turn it on. If you save your flight it should be on the next time you load it.

I have a faint memory that the avionics in the sim are accurately modelled - ie they're powered by the battery not the generators so you need your battery master switch on too. Of course that means that if your battery goes flat the avionics die and your vPilot radios die along with them. It can be puzzling if you don't know this and just happen to have your Avionics Master Switch on. If your engines are off your vPilot radios will work until the battery goes flat, then they'll stop working but it won't be obvious why. However your gens should keep the battery topped up, so getting your APU and its generator on asap should work around that.

If you're interested I was told this by a 737 captain in relation to the real plane:-

"The 737 doesn’t have an avionics master switch as such - the vital instruments and radios (captains PFD, ND, FMC1, Comm and Nav 1, stby instruments) are wired into the battery bus so as soon as the battery switch is turned on, they get powered up. Once an AC source is connected, either via the APU or ground power, a number of bus tie breakers close and all the avionics come online. So from a switching point of view, battery switch to ‘on’ brings DC powered instruments online and when APU or GPU are switched to come online, the remainder of the aircraft comes alive."

All the best,