What was found
(CAN) DURING FLIGHT, PILOT REPORTED THAT NP RPM INDICATION WAS FLUCTUATING. NP WOULD DROP TO AROUND 1620 FOR A FEW SECONDS & THEN IT WOULD RETURN TO IT'S CONSTANT SPEED RANGE OF AROUND 1700. FLUCTUATIONS LASTED FOR ABOUT 20 MINUTES. TORQUE & FUEL FLOW WERE CONSTANT & NO SURGING WAS FELT BY PILOT. PILOT LANDED AT NEAREST AIRPORT. NP INDICATION SYS WAS INSPECTED, & RPM CONNECTOR CLEANED ON CSU. A/C WAS GROUND RUN AND NP INDICATIONS WERE NORMAL AND CONSTANT. A/C RETURNED TO BASE. RETURN FLT, & FURTHER INVESTIGATIONS & GROUNDS RUNS AT BASE, NP SYSTEM FUNCTIONED NORMALLY. AFTER 22 HOURS OF FLIGHT OPERATION, PROBLEM HAS NOT RETURNED. BELIEVE THE PROBLEM WAS RPM CONNECTOR ON CSU, SINCE OTHER PC-12 ENGINE CONNECTORS