Lycoming Carb Heat

"Mitty" wrote in message
...
I am about to get checked out in a Civil Air Patrol 172 that has an STC'd
O-360 installed in place of the original Lycoming O-320. The 172 POH
wants carb heat on approach. This makes no sense to me. If I have to do
a go around it is just one more workload item/one more thing to forget
and, from my Piper experience, it does not appear to be necessary. My
guess, without benefit of any actual facts, is that this POH requirement
comes from Cessna's Continental roots and has no engineering
justification. So it seems wise to ignore it.

I'm not familiar with the 172, but in the PA-28s I fly I was taught always
to have carb heat on when below 2,000rpm, which would certainly be the case
on an approach - so much so that checking/adjusting the carb heat setting is
now a ritual that I subconsciously carry out whenever changing the power
setting.

At 300 feet or so, though, you'd switch it to "cold", mainly to give you
maximum power in the event of a go-around, but also in the knowledge that
having the carb heat on means you're getting some unfiltered air into the
engine, and the air can be quite mucky at, or just above, ground level.

D.