What was found
RT PROPELLER RPM DECREASES TOWARD FEATHER BEFORE PROP CONTROL IS BROUGHT BACK INTO FEATHER DETENT. FOUND JAM NUT ON FEATHER SPEED ADJUSTMENT SCREW HAD WORKED LOOSE AND THE ADJUSTMENT SCREW WAS BACKING OUT. THE DESIGN OF THESE NUTS HAS BEEN CHANGED IN THE LAST FEW YEARS, THE EARLY TYPE DID NOT SEEM TO LOOSEN. IF THE ADJUSTMENT SCREW HAD CONTINUED TO BACK OUT, THE ENGINE COULD HAVE EXPERIENCED AN UNCOMMANDED FEATHER WITH LITTLE OR NO WARNING. SUGGEST CHECKING TORQUE OF JAM NUT AT EACH INSPECTION AND APPLICATION OF TORQUE PUTTY UNTIL BETTER RETENTION SYSTEM IS DEVELOPED. (K)