What was found
PILOT REPORTED LOW AND FLUCTUATING OIL PRESSURE FROM LEFT ENGINE IN FLIGHT AND ELECTED TO SHUT THE ENGINE DOWN. AN UNEVENTFUL SINGLE ENGINE LANDING WAS MADE. THE ENGINE OIL BYPASS VALVE WAS FOUND TO BE IN THE "POPPED" CONDITION, THE OIL FILTER WAS THEN REMOVED AND FOUND TO BE BLACK IN COLOR WITH THE FORWARD SEALING SURFACE BROKEN IN SEVERAL SMALL PIECES. THE REDUCTION GEAR BOX WAS DISASSEMBLED AND THE OIL PRESSURE PUMP REMOVED. THE FORWARD HOUSING WAS CRACKED APPROXIMATELY (3 INCH) RADIALLY AT FWD DETAIL. (K)