On Mon, 29 Sep 2003 00:16:00 -0700, "Fred E. Pate"
wrote:

John Bell wrote:
Let me add two links to the discussion:

This is on problems with cold weather altimetry:

http://www.aircraftbuyer.com/learn/train06.htm

This is about the accuracy of unaided GPS altitude in the context of
vertical guidance, but it bears some relavence to the discussion of the
accuracy of GPS altitude:

http://www.bluecoat.org/reports/Graham_2001_RawGPS.pdf

John Bell
www.cockpitgps.com


This one's for the Canadians on this thread. A notice on the new
Oakland, California (KOAK) "RNAV (GPS) RWY 29" approach
(http://www.myairplane.com/databases/.../OAK_agr29.pdf):

"BARO-VNAV NA below -15 deg C (5 deg F)"

And this is for a decision altitude of only 294 ft AGL. Seems like the
FAA is moving towards taking into account temperature errors in
barometric alitmetry. And, by implication, this supports the premise
that WAAS altitude figures are more accurate than the trusty old
"sensitive altimeter." (In the legend they specifically state that
WAAS-based VNAV can be used when BARO-VNAV is not approved due to
temperature.)

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

OTOH with those temperatures we either have severe clear, or blowing
snow. It's rather uncommon to see clouds near the ground when it's
that cold here in the flat lands.

That and you can be "on top" of a raging blizzard at 4,000.



Roger Halstead (K8RI EN73 & ARRL Life Member)
www.rogerhalstead.com
N833R World's oldest Debonair? (S# CD-2)