yes - you don't want to leave it turned on without adequate airflow to
dissipate the heat buildup. The things get hot enough to melt the 1/4"
plastic tubing that connect most of them to the P/S system. I had a P/S
failure just prior to rotation on an ITO in Seattle years ago because of a
looong hold with the heat turned on. Luckily the student in the left seat
had paid attention during training and aborted the takeoff when the airspeed
went to zero. A perfect training lesson for the student and a lesson in
reality for the instructor.

Typically now we turn on the heat as we taxi into position and then turn it
off during the taxi in to the ramp. Feel of the pitot tube some time after
the heat has been on for a while -- but do so carefully because you can get
burnt on some of them.

--
Jim Carter
Seen on a bumper sticker:
If you can read this, thank a teacher
If you can read this in English, thank a soldier.

"K. Ari Krupnikov" wrote in message
...
Coming back from Mammoth this past Sunday and flying through a snow
cloud West of the Sierras, I had the Pitot freeze over. I realized it
was frozen when I tried to correct for altitude gained in turbulence
and the airspeed indication didn't increase even as I pushed the nose
down and could hear the relative wind increase. Not a big problem -- I
could see where I was going on the AI, and a minute or less after I
turned Pitot heat on, ASI returned to normal.

This did raise a question -- is there a good reason Pitot heat isn't
on all the time? It doesn't seem to be a big power drain, and unlike
carb heat does not to my knowledge affect performance. Is there a
reason I shouldn't turn it on when I put transponder on ALT and turn
it off when I shut down electrics before engine shutdown?

Ari.

--
Elections only count as free and trials as fair if you can lose money
betting on the outcome.