GPS Altitude with WAAS

Okay. But if you're on a precision approach you'll be below the inversion, no?

Mike Rapoport wrote:


I agree in principle but in actuality it never gets cold enough in the US to
make a difference. The only times that we have really low temperatures (-40
and below) there is an inversion.

Mike
MU-2

Mike Rapoport wrote:
The pigs will be flying long before there is a 5F day at OAK.

Mike
MU-2

Oh yeah, I forgot to add that those pigs will be using WAAS and LAAS
equipment to make their approaches into Oakland when it happens

Roger Halstead wrote:

It seems a bit strange...
.
DH on the ILS at MBS is only 200 feet AGL and that is with no
temperature correction. In the winter we regularly see below zero
F and it's not rare to see it at minus 20 at night


Yup, but temperature doesn't effect the glideslope, just where you put
the MAP along that glideslope. On the so-called "Baro-VNAV" approaches,
the glideslope is defined using barometric altimeter data, so the entire
glideslope will be shallower and closer to the ground on a cold day.
And if there is a low-level temperature inversion the glideslope won't
even be a straight line.