20010917029189A

(-23) At 6000 feet MSL, in cruise flight, on an IFR flight plan from orl to ocf, crew noticed oil pressure reading zero and low oil pressure light illuminated. The CFI decided to attempt return to Orlando executive airport, approximately 35 NM to the se. The crew overflew two nearby airports on their return to orl. At 3500 to 3000 feet MSL the engine seized. The CFI initially planned a forced landing to a busy highway. He changed his mind and landed in a marshy area adjacent to the highway substantially damaging the airplane. (.4) during cruise flight the engine lost oil pressure and the pilot continued to fly in an attempt to get back to his departure point, however the engine seized before the pilot could reach the departure point. The pilot made a forced landing into unsuitable terrain substantially damaging the airplane, however, the pilot and pilot rated passenger were not injured. Examination of the engine found the two bottom attachment screws for the upper (left) vacuum pump loose. Approximately one quart of oil was found in the engine and oil filter. The underside of the airplane was coated with oil from t he firewall to the tail mooring point. No anomalies were found with the oil pump or oil lines. A review of the airfrane maintenance logbooks revealed that the left vacuum pump and been removed and replaced on the same day of the accident prior to the accident flight. An oil leak test was performed on another 172R. The two lower nuts of the upper vacuum pump were loosened and the engine was run near full static RPM for five minutes. Oil began leaking from the vacuum pump as soon as the engine was started. After five minutes, the back of the engine, the lower cowling, engine accessories and the ground were partially covered with oil. According to the Cessna pilot operating handbook under emergency procedures, the pilot's should have landed at the nearest airport to inspect for the source of the loss of oil pressure.