Rockwell S2R N8468V accident near Royal City, Washington

Probable cause

The loss of engine power due to the separation of the No. 2 cylinder exhaust rocker boss housing, which prevented the exhaust valve from opening.

NTSB analysis

The pilot stated that shortly after taking off for the aerial application flight the engine began to run rough. Because he could not maintain altitude and was concerned about clearing a set of power lines in front of him, the pilot partially dumped the airplane’s aerial application load. After the airplane cleared the power lines, the pilot attempted to land on a road; however, during the touchdown the airplane veered off of the road and into a ditch. A postaccident fire consumed the airplane. A postaccident examination of the engine revealed that the No. 2 cylinder exhaust rocker boss housing had separated from the cylinder, which prevented the cylinder's exhaust valve from opening and resulted in the loss of engine power. Maintenance records revealed that the cylinder had been inspected in accordance with the time interval specified by the applicable Federal Aviation Administration airworthiness directive (AD). The AD specifies a 100-hour recurring inspection requirement; the engine had accumulated 91 hours since its last inspection.

Text from the NTSB. Open the NTSB docket for WPR12LA356 for the full record.