Mr S,
I'd certainly follow all the good advice here,
but if a power assurance comes in negative, carry out instrument checks first before you start (expensive) work on the engine. Dead-weight test on the torque indicator, Barfield check on the ToT indication, calibration on the Ng gauge: even a pressure test on the altimeter could be worth the effort if the engine is actually healthy, and the instruments are wrong. Has this engine always given these figures, or has there been a noticeable deterioration over a period of time?
Mind you, it can sometimes work the wrong way: some time back we had an S76A with a negative engine. After a Barfield calibration, Chief Engineer decreed that all 6 ToT indicators were to be ignored for both engines, and revised manually by some 20C. Needless to say, the Barfield was out of whack, and we still had an engine change
