Simple rule
As a general rule, if it's an airplane use AM mode. For all else
use FM. For anything that is a broadcast station (like FM radio 88-108, or
TV, use Wide FM setting if available).
Exceptions: Mil Air Band Sat. Downlinks = FM, Shortwave Broadcasts = AM, and the
good old AM band (500-1800, give or take) = of course AM.
Happy Scanning!