Cessna A188B N9496G accident near Pine Bluffs, Wyoming

Probable cause

A partial loss of engine power during takeoff for reasons that could not be determined because postaccident examination did not reveal any mechanical malfunctions or failures that would have precluded normal operation.

NTSB analysis

The newly hired commercial pilot intended to conduct a solo practice flight in the piston-engine, agricultural-agent-dispensing airplane. It was the first flight of the day for the pilot and airplane, and his first flight in this particular airplane. Because the airport elevation was about 5,100 feet above mean sea level, the pilot leaned the fuel-air mixture, then conducted an engine run-up. The pilot reported that the run-up was normal and that he set flaps at 5 degrees. The target climb speed was 80 mph. The initial portion of the takeoff roll was normal but then seemed to continue for an “abnormal length of runway.” The pilot did not abort the takeoff because, by the time he recognized that the airplane was not performing adequately, he believed that there was insufficient runway remaining to stop. The airplane lifted off, but then the engine seemed to experience a partial loss of power, and the pilot was unable to fly the airplane out of ground effect after it crossed the departure end of the runway. The pilot jettisoned the payload and conducted a precautionary landing in a field off the end of the runway to avoid a collision with power lines. Review of maintenance records found that the engine exceeded the recommended time between overhaul by 470 hours. However, examination of the airplane and engine did not reveal evidence of any preimpact mechanical malfunctions or failures that would have precluded normal operation. The appearance of the engine spark plugs was consistent with the engine being regularly operated with a fuel-air mixture that was leaner than normal, and the possibility that the pilot improperly leaned the engine for the takeoff could not be ruled out. The takeoff performance data in the airplane manufacturer's operating manual was insufficient to determine the expected performance for the airplane’s reported configuration and ambient conditions. The available performance data suggested that the airplane should have been able to climb out of ground effect and that the target climb speed used by the pilot might have been too high; however, the available information was inconclusive with regard to both these issues.

Text from the NTSB. Open the NTSB docket for WPR11LA253 for the full record.