Accident Narrative
The pilot reported fueling the airplane himself from his own fuel tank the day before the accident. On the accident day, the pilot and one passenger departed for a 20-minute uneventful flight to another airport, where an additional passenger boarded. During climbout at 6,500 feet msl with the autopilot engaged, the VFR pilot observed adverse weather ahead on the airplane's stormscope. The pilot disengaged the autopilot and turned 90 degrees left to avoid the weather. The flight subsequently entered IMC conditions and encountered a downdraft, losing 2,000–3,000 feet of altitude. Following this, the airplane met an updraft, during which airspeed decreased and the engine ceased operating. The pilot maintained a nose-low attitude, set the mixture control to full rich, and activated the auxiliary fuel pump in an effort to restore engine power, but power was not regained. The pilot executed a forced landing in a planted millet field.
Post-Accident Examination
During airplane recovery, 28–30 gallons of fuel were found in the left fuel tank, while no fuel was detected in the right fuel tank. The right fuel tank was later discovered to have a crack. No fuel leakage was observed at the accident site from the initial touchdown point to the final resting position. No fuel stains were present on either the upper or lower surfaces of the right wing. Both fuel tank vents were clear, and the fuel lines from each tank to the wing center section had no obstructions. A temporary fuel tank was connected to the fuel selector valve; with the valve selected to both left and right positions, fuel flow was noted at each fuel injector nozzle.
Engine and Component Findings
Engine examination revealed continuity of the crankshaft, camshaft, and valve train, with no evidence of insufficient lubrication. The impulse couplings on both magnetos were broken. Metallurgical analysis of the broken components indicated that, except for the main spring from the impulse coupling of the left magneto, all fracture surfaces showed overstress failure. The main spring of the left magneto impulse coupling exhibited fatigue signatures; the spring met specifications for material, width, and thickness. The roll trim motor actuator was positioned to compensate for a left-wing-heavy condition.
Additional Information
According to a representative of the engine manufacturer, the damage to the impulse couplings for both magnetos was consistent with the magnetos having been operated at speeds below 450 magneto rpm for an extended period. The airplane was equipped with a fuel caution light that would illuminate if one tank were empty and the other tank held less than 14 gallons of fuel; the light would not illuminate if one tank was empty but the other held more than 14 gallons.