Michelle,

I just want to know if the airplane is in front of me or
behind me and at what altitude.


Well, for the last part (altitude - and distance), you'll have to sepnd
less than 1000 $ - the Monroy ATD-300 and the Surecheck portable units
are your option.

For any kind of direction, think upwards of 7000 bucks and installed
units. The Ryan and BFGoodrich (or whatever they call themselves these
days) units do that.

--
Thomas Borchert (EDDH)