NAVION PLT MADE AN EMER LNDG WITH CANOPY OBSCURED WITH OIL DUE TO A PROP DIAPHRAGM LEAK.

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CLRNC WAS OBTAINED WITH AN INITIAL CLB TO 6000 FT MSL. APPROX 2 MINS AFTER LEVELING OFF AT 6000 FT MSL; BEGAN TO NOTICE FINE OIL MIST ON FRONT WINDSHIELDS. ADVISED APCH OF SITUATION AND REQUESTED IMMEDIATE RETURN. CLRNC RECEIVED AND EXECUTED 180 DEG TURN TO R. SITUATION RAPIDLY DETERIORATED AS BOTH FRONT WINDSHIELDS BECAME FULLY OBSCURED IN OIL. ACFT ENG OIL PRESSURE AND TEMP GAUGES NORMAL. CONTACTED APCH AND REQUESTED PRIORITY HANDLING TO ZZZ. CLRNC OBTAINED AND THEN INSTRUCTED TO CONTACT TWR. CONTACTED TWR AND ADVISED THEM OF OUR SITUATION. TWR WANTED TO KNOW HOW MANY SOULS ON BOARD AND FUEL REMAINING IN HRS AND WHICH RWY WE REQUESTED. REQUESTED RWY 25L AND TO ROLL THE CFR EQUIP. BOTH FRONT WINDSHIELDS STILL TOTALLY OBSCURED IN OIL; AND NOW CANOPY SIDE WINDOWS BECOMING OBSCURED IN OIL. THEREFORE; REQUESTED RWY 30 DUE TO THE FACT THAT IT IS THE LONGEST AND WIDEST RWY AT THE ARPT; AND IS ALSO SERVED WITH AN ILS APCH. FORWARD VISIBILITY CONTINUED TO BE ZERO. ENTERED ON L BASE FOR RWY 30 BUT HAD TO EXTEND BACK ON THE DOWNWIND TO LOSE ALT AND AIRSPD TO LOWER THE LNDG GEAR AT 100 MPH. L TURN TO INTERCEPT FINAL APCH COURSE. AS ACFT SLOWED ON FINAL APCH; OIL CLUNG TO ALL WINDOWS. FORWARD VISIBILITY ZERO; PERIPHERAL VISION MARGINAL. ATTEMPTED TO OPEN CANOPY WITHOUT SUCCESS. PERFORMED ZERO FLAP LNDG WITH PWR AND MINIMAL SINK RATE UNTIL ACFT LANDED. ACFT STAYED ON THE RWY AT ALL TIMES. OPENED CANOPY; TAXIED OFF ACTIVE RWY AND SHUT DOWN ENG. POSTFLT INSPECTION REVEALED NO DAMAGE TO ACFT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: PLT STATED THAT THE OIL LEAK WAS CAUSED BY A FAILURE OF THE PUMP DIAPHRAGM IN THE PROP CTL UNIT.