In order to record everything that is said in the cockpit, I connect the audio with a Video Recorder Adapter -GA/Helicopter, from Aircraft Spruce -
HEADSET ADAPTERS AND EXTENSIONS from Aircraft Spruce.
It goes into your planes headphone socket and splits the feed so that you can get the sound into your camcorder/recorder's mic socket.
You can connect it to the rear passenger sockets - if you have any - to keep the cables out of the way.
Have a listen to the sound on one of my flights:
YouTube - Flight from Barton to Caernarfon
or the second half of this video:
YouTube - Flight from White Waltham