[Babul]

how far did you set the distance? get yourself a parachute/maverick, and fly towards the (invisible yet) plane. if the plane appears at half the way, then you have to increase the streamdistance by another 300 units. i suggest 1000 units for a first try. if it works, decrease it again.
edit: the heliport seems to be at 1/4 distance instead 1/2. therefore the distance 450 or 500 will work already.