"Mike Rapoport" wrote in message
k.net...
Many, if not most, turbine airplanes have this but it requires an airdata
computer system. You can set it to arrive at a particular point at a
specific altitude. You need an airdata system as long as you are climbing
or descending to a pressure altitiude. WAAS could only guide you to a GPS
altitude.


Does it really drive the glideslope needle?

Some of the more sophisticated GPSs have VNAV functionality, and turbine
aircraft FMSs almost certainly do too, based on a barometric altitude input.
But I always thought there was a reluctance to put the information on the GS
needle because the glideslope of an ILS is generally associated with a
trajectory with terrain clearance -- something that simple VNAV can't
guarantee.

Julian Scarfe