Newps wrote:

Has nothing to do with traffic levels. We were a TRSA here at BIL and
went right into class C when that all happened across the country. A
very few just stayed TRSA's. Class D is never an option for a facility
with a radar approach control.

It may have been an option at one time. Not all TRSAs are leftover
from the old days. I recall that Fairbanks, AK had an approach control
and class D back in '99 (no TRSA). Looks like they've added a TRSA
since then.

John Galban=====N4BQ (PA28-180)