responding to Lu- (what is taught about rotor divergence and how to correct it)- SFAR 73 is what is taught. the premise being, at least in the case of divergence, that low rotor rpm = loss of centrifugal force. centrifugal force being the only thing keeping the blades in their proper plane. does the R22 have a predisposition to rapid rotor rpm fluctuation? you bet. the SFAR attempts to reinforce recovery procedures.