What happened
While descending at approximately 900 feet MSL and preparing to enter the airport traffic pattern, the pilot reported that the aircraft began an abrupt, uncommanded roll to the right. The pilot attempted to regain level flight by applying full left aileron and full left rudder; however, the aircraft maintained a right wing low attitude and continued in a gradual right turn.
Recognizing that directional control was compromised and noting the high density of housing near the airport, the pilot elected to perform a forced landing in a cow pasture. Following the landing, the aircraft impacted a drainage ditch. The pilot was not injured.
The investigation
Post-accident examination of the fuel system showed that the fuel tanks had not been breached. The left fuel tank remained full, while no fuel was found in the right fuel tank. The fuel selector handle was found in the position for the "right tank." During testing, approximately 1 ounce of fuel was drained from the forward fuel filter and about 1/3 of a pint was drained from the aft fuel filter.
The flight controls were examined and found to be in serviceable condition and operating normally. An examination of the propeller revealed that one blade was straight and clean, while the other blade was scratched and bent aft 30 degrees.