What was found
(CAN) EVERY 20 SECONDS IN FLIGHT, PROP SPEED DROPS BY 10 RPM AND ALL OTHER ENGINE PARAMETERS ALSO DROP. CREW COULD FEEL THE DROP IN POWER, NOT AN INDICATION PROBLEM. FADEC WAS REPLACED, ON GROUND HIGH POWER RUNS NO DEFECT NOTICED. TAKE-OFF WAS FINE, BUT ON CLIMB, PARAMETER FLUCTUATIONS RESURFACED EVERY 20 SECS. NR 1 ENGINE SHUTDOWN AND AIRCRAFT RETURNED TO BACK BASE. PCU CHANGED AND CHECK FLIGHT WAS SUCCESSFUL, AIRCRAFT RETURNED TO SERVICE.