This follows from http://thread.gmane.org/gmane.games.flightgear.devel/77932.
With the introduction of the 3D sound engine, all sound files in FlightGear now
must be mono point sources.
The following original sound files have been preserved by renaming to
*-stereo.wav, as the information content in both stereo channels are similar but
non-identical, and mono versions created by extracting the left channel:
- Sounds/apache.wav
Note that audacity was used to convert the Sounds/apache.wav file into a WAV
format readable within FlightGear.
