If you want to do it more professional, use SeAnVeR's
method, but instead of switching the chopper's waypoint
(it would be hovering in the air all the time), rather do
it with the crew (not boarded yet).
Create an empty chopper
create the crew (could be 1 pilot, 1 gunner - or only the
pilot)
Now give the crew a waypoint (type: HOLD) close to the
chopper. place the next waypoint directly onto the chopper
(type: GETIN), and continue with giving waypoints for
your airstrike.
Now syncronize (press F5/drag line) the HOLD waypoint with
the trigger, and whoop the chopper isn't stupidly hovering
anymore.
~S~ CD