According to CS 29.143 and CS 27.143 - Controllability and manoeuvrability:

• The rotorcraft, after failure of one engine, in the case of multi-engine rotorcraft that meet Category A engine isolation requirements, or complete power failure in the case of other rotorcraft, must be controllable over the range of speeds and altitudes for which certification is requested when such power failure occurs with maximum continuous power and critical weight. No corrective action time delay for any condition following power failure may be less than:

(1) For the cruise condition, one second, or normal pilot reaction time (whichever is greater); and

(2) For any other condition, normal pilot reaction time.

NOTE:

Reaction time is the time taken by the pilot after the decision on the appropriate corrective action until commencement of the recovery action.