"David W" wrote:

[snip]

And is it true that such aircraft's navigation systems use maps
'optimised' for GPS?

What does 'optimised' for GPS mean?

I'm not sure. Somebody with whom I am having a 'debate' has asserted
that there is an altitude-dependent error component (if I may call it
that) on positions determined by GPS (and I presume that this alleged
error component affects the horizontal component of a 3D position, as
well as vertical (altitude) component). In his own words:

"GPS is optimised for sea level, Blanchefort [a mountaintop ruined
castle] is 467 metres above sea level, couple this with a slant range
to a satellite of several thousand miles and the curvature of the earth
and you have error. At least up to 100 metres..."

Nonsense. Your opponent in the debate is a ninny.

I personally can find no evidence which supports his claim that a) GPS
is optimised for sea level, or b) GPS coordinates obtained at a few
hundred metres above (mean)
sea level are affected by his alleged altitude-induced error.

[snip]

His reply (with some non-essentials removed):

"Aircraft ... are using a map optimised to the GPS system and this is
the key point which seems to be passing you by."

Utter twaddle. There are no such maps.

What's behind your questions; what are you trying to get at? If you
posted
that, you might get more suitable answers.

I hope that that is sufficiently answered above. I didn't want to
burden this group with extensive background information and endless
quotes from this slightly silly debate!

No problem. You came to the right place after your opponent introduced his
bogus aviation arguments.

--
Dan
C172RG at BFM