Flying with default ATC giving vectors, the aircraft (Autopilot, FMC or whatever) dials to another frequency after 30 to 60 secs. all the time, so one looses connection to ATC.
Have an example here:
https://youtu.be/L6f8uYyTE8s

Very frustrating error since it makes flying the 737 very demanding, always setting back the frequency to get instructions.

I made an interesting observation recently. I suspect FSUIPC autosaving the flight every minute changes the frequency. I switched it to 3 min and it occured less and then switched it off completely. I have to do more flights to be sure it is the cause. Still can't explain why this happens with this plane only. Maybe somebody from CS can think about it and maybe solve it. The old CS 737-200 doesn't have this problem.
I like the autosave option, if the sim crashes short before landing at the destination, one can restart after solving the crash problem.

Dan

I´m pretty sure about FSUIPC making the aircraft changing ATC frequency on every autosave of the flight. I made two flights without autosave, no problem. Now I switched it on and soon after it changed the frequency. Switched it off again, frequency remains as dialed.

It is not an fault of FSUIPC, since no other plane shows this behavior than the Classic.

I have another follow up: I had a frequency change when I manually saved a flight in flight. So it has nothing to do with FSUIPC but saving the flight. Weird.

Hi,

I found this same issue having bought the a/c in the sale. The way to resolve this for me is to select the same frequencies in both boxes. So box one say 122.800 and 132.600. Then the exact same in box 2. When flying online and been asked to change frequency, I only select Box 1 left hand side with the new frequency and copy this into the left hand of box 2 frequency. Both secondary frequencies  must stay the same as mentioned above.
This works for me most of the time say 90%. Another thing I do is to use the keyboard 9 key which brings up Box 2. Here I can see if there have been any strange changes without ATC moaning at me.

Hope this all makes sense!

Keith