Snowbird wrote in message There's also the vis. factor. If it's hazy and
you're flying towards the sun, you can't see a durn thing even if there
isn't a cloud out
there. OTOH, a plane flying perp. or away from the sun can legitimately
see 3+ miles

Last weekend, I flew up to North Carolina at 16,500'. I try to put one of
the local flight instructors in the seat when I can. It was a hazy summer
day, but the co-pilot of the day had no problem maintaining straight and
level, staying out of the clouds, and spotting landmarks. However, the TCAD
(traffic collision avoidance thing) would show an occassional target being
within 3 miles of us and we couldn't see them for nothing.

D.