Event Description
During a climb through 9,000 feet mean sea level (msl), the pilot leaned the fuel mixture relying solely on the exhaust gas temperature gauge. At about 9,500 feet msl, approximately 1,500 feet above ground level over mountainous terrain, the pilot reported that the engine lost partial power. The propeller continued to rotate, and the tachometer indicated between 2,450 and 2,500 rpm, but the engine did not produce enough power to sustain level flight.
The pilot adjusted the mixture control, turned the carburetor heat to the on position, and applied full throttle. The engine failed to respond. The pilot then made an approach to a sandy beach. During the landing, the pilot flared the airplane about 2 feet above ground level. The left wing struck a tree stump, causing the airplane to veer to the right. The elevation at the crash site was approximately 7,600 feet msl.
Post-Accident Investigation
A post-accident examination of the engine revealed that the left magneto exhibited excessive play at the cam end (points) of the main shaft. Functional testing of the magneto showed an intermittent spark on ignition lead T1. According to Textron Lycoming Mandatory Service Bulletin 515, magnetos must be inspected every 500 hours. At the time of the accident, the magneto had accumulated 1,540.23 hours of total time in service, and there was no maintenance record indicating compliance with the service bulletin.
While post-accident tests demonstrated that the left magneto was operating only intermittently, information provided by Lycoming suggested that a complete loss of one magneto would result in only a 3 to 5 percent loss of power. The investigation determined that it is likely that the combined effects of the magneto malfunction, the high density altitude, and the pilot's manipulation of the mixture and carburetor heat all played roles in the engine's decreased performance capability.
Probable Cause
The probable cause is the combined effects of the magneto malfunction, the high density altitude, and the pilot's manipulation of the mixture and carburetor heat, all contributing to the engine's decreased performance capability.