Hi Dave,
With an external antenna, I suspect the coverage will be very similar to aviation band radios. Using the 'rubber duck'... likely about 1/3 of that range because of the decreased efficiency of the antenna and the shielding effect of the airframe. Also, just as with flying over large bodies of water, when it comes to radio signal range at VHF and UHF frequencies, height is your friend.
I hope the next step in avaition radio is to combime one with an amateur rig like this one. There may be some regulatory reason not to do it, but if they do build one.... I'm in!!!
-Dan