AW 139 Cat A Ops
"1. The optimum Nr for rotor performance is 100% (any more or less and the rotor is LESS efficient)
2. In order to meet the RFM Cat A performance standards, any OEI flight during take off and landing must be conducted with the remaining engine at maximum power.
3. To ensure that this is so, the collective lever must be raised until the Nr droops. This will bring the remaining engine up to maximum power. If the remaining engine is NOT at maximum power then the performance promised in the RFM cannot be guaranteed.
4. If the starting point was 100% Nr then this would mean that when the Nr was 'drooped' to say 98% then the rotor was working at a less efficient speed so the Nr is set to 102%. Thus, when the Nr is drooped it will droop to 100% where it should remain until Vtoss is achieved.
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