NTSB Identification: CHI96LA093.
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Accident occurred Sunday, February 18, 1996 in WORTHINGTON, MN
Probable Cause Approval Date: 05/29/1996
Aircraft: CESSNA 172, registration: N758CQ
Injuries: 3 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

After climbing to 3500 feet, the pilot noted that smoke was entering the cockpit and that the engine was beginning to run rough. He diverted back toward the airport, but noted that the oil pressure began dropping rapidly and that the RPM began to fluctuate. The pilot then decided to secured the engine and make an emergency landing on a gravel road. During the landing, the right wing hit a yield sign on the side of the road. There was no indication of oil on the dipstick. A two to three inch hole was discovered in the crankcase of the engine. Examination of the engine revealed that a hole had been burned through the number three piston; the #1 and #2 connecting rods were off the crankshaft; and the #1 and #2 crankshaft journals were partially melted. The fuel system was checked and no defects were discovered. An examination of the magnetos revealed that the race inside the left magneto was loose and rotating within the aluminum housing. Metal particles from the race and housing covered the surface around the magneto block.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

Progressive failure of the engine, beginning with failure of the left magneto, which resulted in preignition or detonation, a burned hole in the #3 piston, subsequent oil exhaustion, and failure of the #1 and #2 connecting rods.

Full narrative available

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