As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED THAT LT ENGINE RPM CONTINUED TO DECREASE IN FLIGHT. ON APPROACH, ELECTED TO SHUT THE LT ENGINE DOWN. UPON INSPECTION, IT WAS DETERMINED THAT THE LT ENGINE RPM ADJUSTING SCREW SELF LOCKING INSERT WAS LOOSE, ALLOWING SCREW TO BACK OFF DUE TO ENGINE VIBRATION. UPDATE:THE LOWER OUTER SHAFT LEVER WAS REPAIRED BY REPLACING THE SELF LOCKING THREADED INSERT, AND INSTALLING A NEW SCREW.