Cessna 172N N734YW accident near Natchitoches, Louisiana

Probable cause

The partial loss of engine power due to the exhaust valve rocker retaining stud backing out of the cylinder head, which resulted in the exhaust valve being stuck in the closed position. Contributing to the accident was the pilot’s failure to configure the airplane and fly it in a manner that would allow him to make the emergency landing in the field rather than overfly it, and the pilot’s failure to have the engine overhauled according to the recommended overhaul interval.

NTSB analysis

Before departure for the flight, the private pilot/owner reported that he conducted the preflight and run-up and that the airplane was operating normally. During takeoff, he rotated the airplane about 70 kts and the climb out was normal. About 300 feet above ground level, the engine suddenly lost power and shook violently. The pilot scanned for potential emergency landing areas and decided to attempt to land in a soybean field that was about 135 degrees to his left. The airplane overflew the soybean field and impacted a line of trees at the end of the field.

The postaccident examination of the engine revealed that the No. 1 cylinder exhaust valve rocker retaining stud was backed out of the cylinder head threads by about 5 threads, or about ¼ inch, and the valve rocker and pushrod were loose. The clearance between the valve rocker and the valve stem was too great to allow the exhaust valve to open as the engine rotated. The last engine overhaul was conducted on May 26, 1990, and had 958.1 hours of operation since the overhaul. The engine manufacturer recommends that engines that have not accumulated the recommended hourly time between overhauls be overhauled during the 12th year after the last overhaul; it had been over 24 years since the last overhaul.

A postaccident examination of the airplane revealed that the flaps were in the up position and that the flap handle, flap indicator, and the flap actuator were in the up position. Had the pilot lowered the flaps, flown S-turns, or slipped the airplane, he most likely would have been able to land the airplane in the soybean field, avoiding impact with trees at the end of the field.

Text from the NTSB. Open the NTSB docket for CEN14FA435 for the full record.