I don't know if there is a FAR against plugging any recording equipment into the aircraft. Just some food for thought because nobody wants to break a FAR.

Anyhow, on the military side of things, Uncle Sam uses a different plug. In order to connect directly, you need some fancy converters. But there is a simple fix and would apply to your situation.

Get yourself some in-the-ear earphones (the small kind). Plug then into the mic jack of your recorder. Connect a headset to the aircraft and turn the volume up on the headest/audio. Place the ear pieces (which will be acting like microphones and not speakers) inside the ears of the headset. Cover the headset cups with tape, leaving the an ear piece inside.

The ear pieces will record the audio and it works surprisingly well.

-Fatty