I thought the primary factor in determining the differences between
baro altitude and GPS altitude was the difference between "sea level"
and the WGS84 datum plane at the particular location? From my
understanding these two planes of reference are not the same but are
closer in some spots than in others.

Marco

Ron Lee wrote:
john smith wrote:

In article ,
(Ron Lee) wrote:

I made another flight to KFTG this afternoon and periodically checked
the GPS receiver provided altitude versus my aircraft altimeter. GPS
was within 40' every time I checked (closer at times). I need to
check my last altimeter check to see if it has any errors but it is
certainly within standards so GPS is proving to be close enough for
VFR in these cold weather conditions.

Ron, is your GPS WAAS enabled?
My non-WAAS Garmin 195 will only get within 150 feet vertically.
Vertical is the least accurate of the three planes.

Good question. It is a Garmin GNS 430 without WAAS. I should try my
Etrex as well.

Of course I am not advocating using GPS to establish flight altitudes.

Ron Lee