About a week ago I decided to try out the headphone mode again but could not get any sound through the headphones. I had tried it out when I first got the sim and it worked then. Now it doesn't. There is nothing wrong with the phones. Youtube vids and music sound fine. When I go into options and put on the headphone mode and plug in my headphones sound to the external speakers is muted but I get no sound from the sim. After a couple of minutes I get static like I have lost the signal. I am using Sennheiser headphones that have a base transmitting unit that plugs into the computer that sends a wireless signal to the phones.  Is there something else I have to do in the sim settings. As best I can remember I didn't have to do anything special to get them to work before. This could be due to something in the last update a week or so ago. Anyone else in the forum using headphone mode successfully. I am not using multiplayer.

Have you gone to windows settings/sound?

You sometimes have to tell windows the input/output to use. I fly on Vatsim and had to do this too. 

Bluetooth headset often caused an issue as it forgot previous settings, I had to keep resetting each time. I now use a USB headset as its plug and play.

Settings/sound/advanced (you set input/output for MSFS)

Try it.

Ian