Fist thing to check will be your Aircraft Radio or Interface Box. Turn the squelch down to zero and your Mic should be ‘live’ all the time. In this condition, check the Mic Audio is loud and clear, not turning off and without Hum. If all is OK, Check another Headset if you can to check against yours.
The Headset Mic should work all the time like this and not need to raise your voice to work. If it does, suspect the Radio or Interface to have a problem. If the Mic Audio output is low under these conditions, or another A20 Headset works better, then you may need to send it in to Bose for inspection and repair?
You can contact the Service Department through the Bose Website by entering your location?