:hmm: Flyinheight has always worked for choppers.. and even works for planes now.... :hmm:
there must be an error occuring in the way you're using it ...
you could simply try placing this in the heli's init field:
this flyinheight 90
or alternatively you can name the chopper something and use:
choppername flyinheight 90
in a script, trigger, or waypoint