What was found
(CAN) WHILE RETURNING TO BASE AFTER FIRE BOMBING OPERATION, THE NR 2 ENGINE BEGAN TO BACKFIRE MILDLY. A PRECAUTIONARY ENGINE SHUTDOWN WAS CARRIED OUT. POST-FLIGHT INSPECTION FOUND NR 3 CYLINDER SPARK PLUG PEENED OVER. THE DAMAGED NR 3 CYLINDER WAS REMOVED AND A CRACKED PISTON RING GLAND WAS DISCOVERED. THE CYLINDER ASSEMBLY WAS REPLACED. THE ENGINE GROUND RUN SERVICEABLE AND THE AIRCRAFT RETURNED TO SERVICE.