Introduction
An accident occurred when a aircraft, during flight, experienced a loss of control and crashed into a parking lot. Witnesses reported hearing sounds consistent with propeller overspeed followed by engine power being reduced to idle, as if the pilot closed the throttle. The aircraft then banked to the left and entered a spin before impacting the ground.
Witness Observations
According to witness statements, the engine noise changed dramatically, suggesting the propeller was overspeeding. Shortly after, the engine power was reduced to idle. The aircraft then rolled left and entered a spin, descending until it struck a parking lot.
Post-Crash Examination
Investigators examined the engine, aircraft structure, and flight controls after the crash. No evidence of precrash failure or malfunction was found in these components. The examination then focused on the propeller assembly.
Propeller Pin Failure
The propeller examination revealed that the number two blade pitch change actuating pin had failed. The failure was determined to be due to fatigue. The pin had been installed during a propeller overhaul approximately 600 flight hours before the accident. The installation was performed in accordance with McCauley Service Bulletin 99, which, however, is not applicable to this model of propeller.
The installation used a short threaded pin, a thin spacer, and a blind hole in the ferrule. This combination allowed the pin to bottom out in the hole, preventing proper torquing. As a result, the pin cracked under the applied loads during service, leading to the fatigue failure.
Conclusion
The investigation identified the failure of the propeller blade pitch change actuating pin as a result of fatigue cracking caused by improper installation. No other precrash anomalies were found in the airframe, engine, or flight controls.