As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKEOFF, NR 1 PROP CYCLED FROM 1200 TO 800 RPM, COULD NOT BE CONTROLLED UNTIL ENGINE WAS SHUTDOWN AND FEATHERED. AFTER RETURN TO FIELD, MAINTENANCE READ THE FDR, NO OVERTORQUE FOUND. THE ENGINE AND PROP CONTROL LINKAGES WERE INSPECTED, NO DEFECTS FOUND. NO ABNORMAL PARAMETERS NOTED ON GROUND RUN, THE BETA LOCKOUT SYSTEM WAS DETERMINED TO HAVE CAUSED THE PROP RPM FLUCTUATION. BETA LOCKOUT MEL WAS COMPLIED WITH AND THE AIRCRAFT WAS RETURNED TO SERVICE.