What happened
Shortly after departing, approximately five to ten minutes into the flight, the pilot attempted to adjust the mixture to address an engine running roughly. Roughly thirty minutes later, the left engine experienced an overspeed event. During this period, the pilot was unable to feather the propeller.
In an attempt to return to the departure airfield, the pilot utilized maximum power from the right engine. However, the aircraft was unable to reach the airport, necessitating an emergency landing on a highway. During the landing sequence, the pilot lost directional control, resulting in the aircraft striking trees. There were no reported fatalities or injuries in the accident.
Findings
Investigations into the mechanical state of the aircraft revealed extensive issues with the engine and control systems. The left propeller featured a corroded start lock pin in the extended position, and the pitch control cable was found to be frayed, corroded, and separated. Significant wear was also noted in the piston rings and the number 6 connecting rod.
On the right engine, the propeller governor control cables were also corroded and frayed, and the intake pipe connection and hose for cylinder number 5 were missing. Internal engine damage included severely worn compression rings on pistons 1 and 5, as well as seized compression rings on piston 2. Furthermore, there was no documentation indicating that the aircraft had undergone recent inspections by an A&P mechanic or an FAA-approved repair station, as the last annual inspection was recorded in 1978. Additionally, the pilot indicated that the flight manual was not utilized during ground or flight operations.