As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) WHILE IN FLIGHT THE RT ENG BEGANS BACKFIRING WITH LOSS OF POWER. AS IAW COMPANY PROCEDURES THE ENG WAS SHUTDOWN AND THE PROP FEATHERED. EMERGENCY PROCEDURE DECLARED, ACFT RETURNED TO MX FACILITY. AFTER INVESTIGATION WE FOUND THE FRONT SPARK PLUG ON CYLINDER NR15 DEFECTIVE. SPARK PLUG REPLACED AND ACFT BACK TO SERVICE.