NTSB Identification: IAD97LA008.
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Accident occurred Sunday, October 13, 1996 in GERMANTOWN, KY
Probable Cause Approval Date: 10/31/1997
Aircraft: Cessna 172, registration: N8299U
Injuries: 1 Minor.

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

The flight was en route at 5500' MSL, when the pilot noted a loss of oil pressure followed by a loss of engine power. A forced landing was made in an open field, where the airplane collided with a ditch. Inspection of the airplane revealed the lower fuselage was covered with oil. Examination of the engine revealed evidence of oil starvation in the main bearings, connecting rod bearings, and journals of the crankshaft. All of the cylinders were steel-barreled, except the #4 cylinder, which was chrome plated. The #4 cylinder was heavily scored in the chrome barrel, and the #4 piston was scored completely around its skirt. The #4 piston exhibited burning on the lower crown, which eroded a hole to the piston interior below the third piston ring groove. The piston rings were stuck due to aluminum from the piston skirts extruding over them. Heat had expanded the piston skirts into contact with the cylinder walls, scoring them and transferring aluminum from the piston skirt. According to a report from the manufacturer, chrome cylinders must use plain steel rings per TCM service literature; however, the #4 cylinder was installed using rings for a steel barreled cylinder, which have chrome plating on the top compression ring. The manufacturer's report also noted that chrome ring on chrome cylinder bore will not work and could create scoring, metal transfer, and eventually severe blowby conditions. The engine had accumulated 1075 hours of flight time since the last overhaul.

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

improper maintenance with the installation of an improper oil ring on the number four piston, which led to failure of both the ring and pistion, oil starvation, and subsequent loss of engine power.

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