In article .com,
"David W" wrote:

Do most modern aircraft rely on the GPS for navigation, and to what
extent do they rely on it?

define "modern"

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

No.

And finally, if I may, what level of positional accuracy must aircraft
relying on GPS for navigation work with at typical altitudes
(presumably 20,000 to 40,000 ft)? Are we talking tens of metres, or
over a hundred metres?

Currently, the accuracies required are over hundreds of meters.
The tightest restrictions on aircraft operations are currently those
in RNP-4 RNAV airspace. The aircraft must be laterally within
4 nmi of intended course 95% of the time, and have an unannunciated
loss of containment (i.e., break 8 nmi) with a probability of 10-5
per flight hour.

GPS accuracies in the tens of meters are only currently required for
approaches.

--
Bob Noel
Looking for a sig the
lawyers will hate