FLC OF AN LTT TURBOPROP LOST DIRECTIONAL CTL OF ACFT DURING LNDG ROLL RESULTING IN RUNNING OFF THE SIDE OF THE RWY IN A GRASSY AREA. THERE WAS NO DAMAGE TO THE ACFT OR INJURIES TO THE OCCUPANTS.

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AT APPROX 30 MI FROM DEST ARPT; THE LOW OIL PRESSURE LIGHT ILLUMINATED ON THE ANNUNCIATOR. FURTHER INVESTIGATION DISCOVERED THE OIL PRESSURE GAUGE WAS INDICATING LOWER THAN NORMAL; HOWEVER; ALL OTHER INSTS (INCLUDING OIL TEMP) WERE NORMAL. WE ADVISED ATC OF A POTENTIAL PLANNED ENG SHUTDOWN WHILE CONTACTING OUR MAINT. MAINT SUGGESTED THAT WE CONTINUE WITH BOTH ENGS RUNNING AND TO MONITOR OIL TEMP CLOSELY. AT THIS POINT; WE WERE ESTABLISHED ON THE LOC AND REQUESTED THE STRAIGHT-IN ILS. DURING THE APCH BRIEF; WE MADE A PLAN TO REQUEST A HOLD AT THE OM IN ORDER TO SHUT THE ENG DOWN UPON RECEIVING ANY ADDITIONAL SIGNS OF AN ENG PROB. WE BROKE OUT OF THE APCH AT 1000 FT AGL AND PROCEEDED TO TOUCHDOWN WITHOUT ANY NOTICEABLE CHANGE. UPON LNDG; THE ACFT WAS BROUGHT FROM FLT IDLE TO GND IDLE; AT WHICH POINT IT STARTED TO VEER TO THE R OF CTRLINE. ADDITIONAL L REVERSE WAS APPLIED WITH NO EFFECT TO STEERING. THEN DIFFERENTIAL BRAKING WAS APPLIED WITH ONLY PARTIAL AID IN DIRECTIONAL CTL. THE ACFT EXITED THE RWY ON THE ADJACENT GRASS WHERE IT CAME TO A STOP WITHOUT DAMAGE OR INJURIES. THE ACFT WAS SHUT DOWN AND THE PAX WERE EVACED. AFTER THE MAINT INSPECTION; IT APPEARED THAT AN OIL SEAL COMPLETELY BLEW UPON LNDG; RESULTING IN NO PROP PITCH CTL. IN THE FUTURE; I WILL BE MORE APPREHENSIVE WITH CONTINUING A FLT WITH A POTENTIAL PROB INTO A CRITICAL PHASE OF FLT. OTHER OPTIONS INCLUDE SHUTTING THE ENG DOWN AND DIVERTING TO A LARGER ARPT.