Accident Overview
During a night dual instructional flight, the airplane experienced a partial power loss, prompting the instructor to execute a forced landing. The maneuver concluded with the airplane colliding with rough terrain.
Investigation Findings
Post-accident examination revealed that the #3 exhaust valve rocker arm attachment stud had failed due to fatigue. The separated stud became lodged under the #3 intake valve mechanism, and the corresponding push rod was found bent. The engine and the failed components had accumulated a total of 2,903.5 hours of operation.
Sequence of Events
The accident occurred at night during a training flight with an instructor and student onboard. Following the partial power loss, the instructor assumed control and attempted a forced landing. The aircraft struck uneven ground, resulting in damage.
Mechanical Examination
Laboratory analysis of the engine components identified a fatigue fracture on the #3 exhaust valve rocker arm attachment stud. This failure allowed the stud to migrate and interfere with the intake valve mechanism, bending the push rod and likely contributing to the partial power loss.