ZikZak writes:

There are a (very) few places in the U.S. where class A does not extend down
to FL180.

.... and more elsewhere in North America. Class A starts at FL230 in
the Canadian Northern Control Area (roughly north of 60 deg latitude,
but with a lot of variation) and at FL270 in the Canadian Arctic
Control Area (roughly north of 75 deg latitude). I think it's
probably a matter of the limits of radar coverage.


All the best,


David