On Sun, 03 Sep 2006 16:11:09 +0100, wrote in
:

FM maintains a low background noise longer than AM and the only
difference is at low signal levels when FM very quickly becomes
totally unreadable. AM can still be heard and understood, depending on
the ability of the person listening. With all the noise in an aircraft
a little bit of low level background noise is not significant.

Thank you for bringing up this information. I believe it is adequate
to overcome any suggestion of switching from AM to FM for aviation
communications.