On Sun, 14 Oct 2007 20:36:03 GMT, "Jim Carter"
wrote:

I used 80K while in Oklahoma where you don't fly in the clouds in summer or
winter very often. When I moved to Seattle I switched to 90K because the 172
likes to make carb ice at 1700 rpm more than at 1900 (90K) and we flew in
visible moisture a lot up there. I didn't like flying holds with the carb
heat turned on. I'd rather use it when necessary at lower power settings.

I had an instrument student that came to me after several hours of work with
other instructors. He was adamant about flying the holds at 75K so I let him
(for a while). During one lesson where we were holding over Kitsap at some
intersection for a while, he had to keep adding power to maintain airspeed
and altitude. He finally figured out that he was picking up carb ice and
applied it full on all at once. I'm sure there weren't more than 10 or 12
revolutions of the engine while it tried to burn water, but that was the
longest "stumble" he'd ever experienced and was an object lesson in forming
bad habits.

You really should be able to fly the holds at various speeds ranging from
best endurance, to low-cruise because sometimes you need the higher speed to
avoid ridiculous wind correction angles. I really think you should plan your
hold speeds based on conditions at the time of the hold. Flight is a dynamic
thing after all.


Great post Jim. Thanks!