What happened
During a cross-country aerial observation mission, the pilot was operating a multiengine airplane on the final leg of a landing pattern. As the pilot decreased power to prepare for touchdown, an unusual sound emerged from the right engine, suggesting the propeller was moving toward the beta position. The pilot attempted to rectify the situation by increasing power, which temporarily silenced the noise, but the sound and a noticeable rightward yaw returned as power was reduced again.
Despite applying corrective rudder and aileron inputs to maintain the runway centerline, the aircraft continued to drift. When the pilot transitioned the engine to idle power over the runway, the rightward yaw persisted. An attempt to execute a go-around using full power failed to stabilize the aircraft, as the plane drifted approximately 30 degrees off the centerline. The aircraft subsequently touched down in a grassy area and struck trees. The impact caused the separation of the right wing, the right engine, and the right propeller assembly. There were no fatalities reported in the incident.
Findings
Investigation of the aircraft's maintenance history showed that the right propeller had undergone an overhaul and reinstallation only two days prior to the accident, having flown for nine hours since that service. While testing of the right propeller governor showed no operational anomalies, the speed settings were found to be incorrectly configured. Additionally, the beta valve travel from its neutral position was measured to be out of tolerance.
While it was noted that this mechanical discrepancy could potentially cause improper oil pressure distribution and subsequent blade angle changes, investigators could not confirm if this was the specific cause during the landing. Due to the extent of the impact damage, the condition of the propeller governor control linkage could not be inspected to determine if improper installation or rigging contributed to the propeller moving into the beta position. Ultimately, the exact reason the right propeller moved toward the beta position during power reduction remains undetermined.