How come GPS reads different

Stefan wrote:
Fred G. Black wrote:

This isn't a concern for en-route operations since everybody's
altimeter has the same "error". It can be a concern for terrain
clearance in the mountains or in some cases instrument approaches in
cold weather since the altimeter reads higher than the plane actually is.


No concern, either. When IMC, there is a safety margin built into the
approaches, and when VMC, there are windows in the copckpit.

Pneumatic altimeters are reliable, independant of any infrastructure and
work without electricity.

Stefan

There is a buffer in the procedure design however given that cold
temperature corrections are published (at least in Canada, ref CAP GEN
p19), it's not unreasonable to assume that there are situations where
they should be used.

Fred.