For what reasons does the RRPM increase during the auto flare ?
Here's one which has caught instructors out.
How about...
Student inadvertantly rolling on throttle and *raising collective!!!! Arghhh!!!!
Particularly in R22, this can be very problematic. The correlator, govenor, increased disc loading (Conservation of angular momemtum or Coriolis - - whatever you call it) and low inertia can all work at the same time to bring up that RRPM, and before you can say,"Jack Robinson!" you have an overspeed to explain to maintainance.
I'll admit, it got me once some time ago, with a commercial student who had just joined to continue training with us/me. What it boiled down to was a difference in my timing and technique to what he'd already been taught. Very frustrating...but at the end of the day, as PIC (and instructor) my fault.
Lesson: Guard the collective and throttle like a hawk until you are sure you are familiar with a new student. (Even one with hours of experience.)
Hope this helps someone out there!
cl12pv2s
*Before anyone tries to flame me for this...(Of course I know raising would normally reduce RRPM)...if raising of the collective from flat pitch (full down collective) the correlator will raise RRPM faster than the increased blade pitch will have any effect in reduceing it. (This is demonstrated in the initial pickup and is the reason for the governor to be on then.)