In rec.aviation.piloting karl gruber wrote:
No. It isn't!

Don't know about the 90B, but my 89B has an input from the transponder/encoder.
You can use it for advisory VNAV. Since the input is pressure altitude, you
need to keep the pressure setting current. Mode C is only accurate to 100
feet though, so you will see it jump up and down by that amount. There is
also a page that shows the GPS calculated altitude. I've never seen it closer
than a couple of hundred feet to the true altitude. (on the ground; it could
be more acurate in the air, but I'd only be comparing it to the transponder
or the regular altimeter and maybe they go crazy in the air, but they always
agree within 100 feet of each other.) Sometimes I fly 50 feet higher or lower
to make the GPS presure-supplied altitude read my assigned altitude so that
my flight-aware track (and ATC) believe that I can maintain an altitude as
well as an auto-pilot.


Karl
"Doug" wrote in message
oups.com...
My IFR GPS, a King KLN90B is connected to the altimeter in my
transponder. It is also adjustable to the barometric setting.


--
Don Poitras