Geoffersincornwall
Of course the aircraft does not realize whether it's flying at 100 or 102%. For AW139 Cat A operations 102% has not been selected to have the best rotor efficiency but to achieve the best Cat A performance. So in this terms the best aircraft efficiency is 102% NR
Actually is FADEC and nothuing else that it'll take care of the power delivered topping the engine at 2.5' rating and giving you always the max power available. Collective has to be kept at the same position most of the times and when needed (at the extreme of the nevelope) pulled in order to droop the rotor as much as required to achieve transitional lift.
You do not need to know whether the engine is at max power, you need to carry out the reccomended procedure. Actually you need to watch NR gauge and not PI. Many conditions will not require max OEI power to carry out the procedure.
If you operate the aircraft within the RFM limitations you'll have huge safety margins at 100% NR in the whole Cat B envelope respecting the certification requirements.
212man
The reason 102% has been selected is not to achieve 100% when the rotor droops but to have a greater inertia reserve down to 90% when is required