NTSB Identification: LAX06LA190.
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Accident occurred Saturday, June 03, 2006 in Antioch, CA
Probable Cause Approval Date: 06/27/2007
Aircraft: Aviat Aircraft Inc Pitts S-2B, registration: N117PS
Injuries: 1 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.

The pilot shut down the engine and force-landed the airplane in a field following a loss of oil pressure while performing an aerobatic maneuver. During the landing roll, the airplane nosed-over in muddy terrain. Post accident examination showed that a portion of the number 5 cylinder piston skirt had fractured and was located within the oil valve. The oil valve works through the means of gravity operated ball valves which includes two balls and a spring. During normal flight, the top ball valve is closed and the bottom ball valve is open. During inverted flight, the opposite is true. In this location, the fractured piece could prevent the ball assembly of the oil valve from seating.

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

The loss of oil pressure due to metal pieces from the number 5 piston skirt in the oil system, which prevented the oil valve top ball valve from seating. The muddy terrain was a factor.

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