It drives the flight director and the autopilot follows the flight director.
I don't know for certain if it drives the GS needle. I am pretty sure it
does.

Mike
MU-2

"Julian Scarfe" wrote in message
...
"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