Also, AM detection is probably more tolerant of mistuning than FM.
There's also the reason why Air Traffic Control use AM and not FM - ie
lack of capture effect.


I suspect it is more historical Ian. Aircraft VHF sets are not VFO
controlled, these days there will be PLL but in the past they were
crystal controlled.


It is not the mis-tuning that is the reason, it is the ability to hear 2
stations when they transmit simultaneously, at least under some
conditions. Also it makes it easier to have a ground station transmit on
the same channel simultaneously from several different locations with
offset frequencies, which would be more difficult with FM.

Jeff