SEA97LA116

The pilot reported that while in cruise flight, he heard a 'pop' from the engine and then felt a vibration. The engine lost partial power and the pilot tried to troubleshoot to find the problem. The pilot was unable to identify the problem and maneuvered the airplane to a nearby airstrip. The pilot stated that he tried twice to land on the 2,950-foot-long airstrip, however, each time the airplane's altitude was too high. The pilot opted to divert to an open field where he maneuvered the airplane to avoid obstructions. During the landing, the landing gear was sheared off and the wings were structurally damaged. During the postcrash inspection of the engine, the number three exhaust valve was found broken at the neck. The head of the valve was found lodged in the exhaust manifold.

On May 20, 1997, at 1100 mountain daylight time, a Piper PA-28-140, N32142, registered to New Life Assembly and operated as a 14 CFR Part 91 personal flight, experienced a loss of engine power. The pilot initiated a forced landing to an open field near Hysham, Montana. During the landing roll, the landing gear sheared off and the wings were structurally damaged. Visual meteorological conditions prevailed at the time and no flight plan was filed. The private pilot received minor injuries and his passenger was not injured. The flight had departed from Miles City, Montana, about one-half hour prior to the accident. The flight was en route to Billings, Montana.

In a written statement, the pilot reported that the flight was at 5,500 feet when the engine "popped" and began to vibrate. The pilot stated that he tried to trouble shoot for a problem but was unable to restore full power. The passenger spotted the Hysham Airstrip and the pilot maneuvered toward the airstrip, however, when the flight neared the airstrip, the airplane was too high. The pilot stated that he maneuvered the airplane to try and land on the airstrip again, however, he misjudged the altitude and the airplane was again too high. The pilot opted to divert to an open field where he again had to maneuver the airplane to avoid obstructions. The pilot stated that at the last minute before touchdown, he turned the airplane to avoid striking some old equipment. The left wing contacted the ground and the landing gear was sheared off. The airplane then skidded to a stop.

The Hysham Airstrip is at an elevation of 2,624 feet. The gravel runway is 2,950 feet long and 55 feet wide.

During the post-crash inspection of the engine, it was found that the number three cylinder would not hold compression. The cylinder was removed and it was found that the head of the exhaust valve had broken away at the neck. The head of the valve was found lodged in the exhaust manifold. The top of the piston displayed evidence of impact damage with the valve head.