N171AS

On March 11, 1997, at 1330 eastern standard time, a Cessna 172, N171AS, sustained substantial damage during a forced landing, following a reported loss of engine oil pressure, near Marquette, Michigan. The student pilot reported minor injuries. The 14 CFR Part 91, instructional flight had departed Manistique, Michigan, at 1230, with a planned destination of Iron Mountain, Michigan. Visual meteorological conditions prevailed and no flight plan was filed.

In his written statement, the pilot reported that smoke started to enter the cabin from the heater vent. He shut the vent and scanned the engine instruments. He noted there was "no oil pressure." The engine "started running very rough and shaking." He "shut the engine down to minimize vibration...established best glide angle" and conducted a forced landing in a wooded swamp. The airplane sustained substantial damage during the landing. The pilot was recovered from the accident site by a U. S. Coast Guard helicopter about 1700.

The Federal Aviation Administration Inspector who examined the wreckage reported that the lower fuselage was covered with oil. He reported that the "lower oil separator hose" was not connected to the wet vacuum pump.

During a telephone interview, the operator of the airplane reported that he had "topped off" the engine oil prior to the origination of the accident flight.

The engine was examined at Teledyne Continental Motors, Mobile, Alabama, on June 4, 1997. The oil sump contained "residual" oil and metallic debris. The number one and two connecting rod bolts were necked and fractured. Corresponding holes were punched in the crankcase. The number one exhaust lifter was located in the sump. The left magneto gasket and starter motor mounting flange exhibited evidence of oil leakage. Combustion deposits in the number three cylinder exhibited evidence of "possible high oil consumption" and both number three spark plugs were oil fouled. The engine oil pump was intact. Crankcase main bearings, journals, and connecting rod bearings exhibited signatures of oil starvation. No evidence of fatigue or progressive failure was noted.