I assume that mountains equates to significantly higher elevations. Study the flight manual limitations and performance charts. Understand the various limits associated with high altitude operations. Performance and maneuverability margins are reduced at altitude. You are more likely to encounter the engine T5 or N1 limit (than the torque limit), and rotor droop can accompany large/rapid increases in collective pitch when operating at or near the engine power limits.
A better way to explain the reduced performance/maneuverability margin is to simply say that with increasing altitude the rotor power required increases while the engine power available decreases. You will be operating at the performance limit when the two become equal.
Last edited by HeliTester; 16th November 2010 at 15:52.
Reason: Expand original post