Is there a requirement for the student to fly at Vmca?
I've only just finished my multi-instructor course, and I don't have my notes to hand, but I seem to recall my instructor on the course teaching me to demonstrate Vmca to the student?
I'm not sure that saying that something "risks an incipient... spin" is justification for not doing it. After all, there is risk of an incipient spin any time you do a stall if the student does not prevent yaw, and this is frequently practiced in aircraft which are not certified for intentional spinning.
Airmanship must surely dictate that this kind of exercise is done at a safe height, though, and also with the instructor having sufficient awareness of the dangers that he prevents a situation developing from which he can not recover. In the example you give, where "the aircraft went into a vicious spin so quickly that the instructor was completely caught off guard", this clearly was not the case - but I'd be willing to bet that the same thing will never happen to this instructor again now that he is aware of the danger!
Thanks for sharing, though - the potential for a spin in this exercise is obvious, but wasn't actually highlighted to me when I did the course. It is definitely something I will watch out for when teaching the multi-engine course though!
FFF
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