Dear Doc, I have to agree with MaxNr. All the info you need about max and min rotor rpm (Nr) should be in the aircrafts Aircrew Manual. This apart the instrument panel will have an Nr gauge clearly marked with the normal safe power-off range. Should the Nr droop below the minimum rpm indicated, all is not lost. It is possible with the collective fully down and by a hard flair of the aircraft to increase Nr back into the safe range from an Nr figure as low as 80%.
Wishing you all a happy and safe PFL when you need it. HeliAv8tor.
[This message has been edited by HeliAv8tor (edited 26 August 1999).]