"Kyle Boatright" wrote in
:

On Christmas Eve, I got to go flying. I took a friend of ours on a
200 nm cross country to drop her off with her family for the holidays.
On the good side, the visibility was as good as I've ever seen in the
Southeast. Probably 150 miles or more. I could see the Smokey Mtns
waay north. Also, on the way "out", there was a 25 knot tailwind, so
that portion of the trip went pretty quickly.

On the way home, I flew down low (3000 -3500' MSL) to duck most of the
wind, but still enjoyed the good visibility. Part of the way home, I
saw a large tower a long way in front of me. I was surprised, because
the tower appeared to be much higher than my cruising altitude. I
didn't remember any extremely tall towers NE of Atlanta, but studied
the sectional several times looking for what my eyes were seeing.
Never did find a particularly tall tower on the sectional.

Anyway, it probably took me 20 minutes to reach the tower and by the
time I reached it, it was well below my altitude, (which hadn't
changed). After a little thought, I realized that the curvature of
the earth had resulted in an illusion that the tower was extremely
tall when viewed from a distance, but was only 1000' AGl (or 1800'
MSL) in reality.

I've heard of this phenomena causing confusion between aircraft
approaching each other at high altitude, but never realized it would
occur with towers and the like when visibility was good. It'll
probably be a long time before the visibility around here is good
enough to see a tower from 50 miles away again.


Well, even at middling altitudes I find it hard to tell the altitude of
other airplanes. I also find it difficult to tell the height of a tower,
even relative to my own altitude. if there's a trick to it aside from
makrking the windscreen with a magic marker, it's eluded me!
The introduction of TCAS was a revelation. NEarby airplkanes that you
might have sron were a couple of thousand above turned out to be lower
than us and vice versa. It's not just me, everyone says the same thing.
I can't see how the curvature of the earth would do it, though. Seems to
me no matter which way you slice that the tower would look lower.




Bertie