I agree on the systems knowledge - if you fail a system by pulling the circuit breaker you need to know what you are doing. But if you are teaching, say, emergency gear extension, you hopefully know the gear system quite well - otherwise, what do you teach the student???
I disagree on that it should not be done (sorry for the double negative).
I will happily pull CBs in training provided - and that is important - I can safely complete the flight if it cannot be reset for any reason, which might well be that it is 30 years old and has not been moved in the last 15 of these. So I would NOT pull the flap CB with full flaps down, but would do it with flaps up.
There are a couple of training scenarios where it is, IMO, essential to pull the CB.
(a) Training a procedure that cannot be performed with the system powered. Example
On an aircraft that has an emergency gear extension procedure that can be done without requiring follow-up engineering work (such as disengaging cranks, refilling blow-down bottles etc.) I would argue that it is part of any good conversion training (or initial retractable training) to actually perform an emergency extension. The way it feels, the amount of pumps on the manual pump / cranks on the handle etc. are all valuable training, and there are some interesting teaching points for beginners. You could switch off the master instead, but that, IMO, is not great given you lose the radios during that time.
(b) Training the recognition of an abnormal condition
If possible, at least once per student, I secretly pull the gear CB on downwind (e. g., in a PA28 Arrow). One of my initial retractable students said "three greens" without looking. Nothing drives the message home as calling for the go-around at 100ft...
As for the "flaps stay down" scenario - I simulate this by secretly reselecting flaps down. But more than half of the students notice.
Last edited by Cobalt; 9th Jan 2014 at 22:49.