The question was IF no radio available to get a corrected
altimeter setting... if a GPS is available the GPS altitude
is better than no correction at all.

If I take-off in a airplane with no radio and fly through a
cold front in VFR, the altimeter setting is likely to change
enough to have a 500 foot or greater error with a 100 mile
flight. A GPS can be used to get closer than that.

Probably, most NORDO flights are at or below 3,000 AGL under
VFR. Terrain clearance is more critical to such a flight
based on the altimeter than is the mid-air collision problem
since the "rule" only applies above 3,000 AGL.

Someday, the rules may change, but within today's rules,
using GPS "as the best available" or only source is better
than no source at all.



"mike regish" wrote in message
. ..
| Well, kind of. Most, if not all altimeters now, compensate
for pressure
| variations to show geometric (if that's the right term for
it) altitude.
|
| With SA disables in the GPS system, altitude is much more
accurate than it
| was. How accurate, I don't know. When I compare my
altimeter with my GPS's,
| they're usually about 100' apart. I'm not sure which is
more accurate.
|
| mike
|
| "Stefan" wrote in message
| . ..
| Jim Macklin schrieb:
| they give altitude, accurate to within a few feet.
just set the
| altimeter to read the same.
|
| NO, dont' do this. The whole aviation system (airspace,
separation...) is
| based on pressure altitude, not geometric altitude.
|
| Stefan
|
|