What happened
During cruise flight, the pilot observed a gradual decrease in left engine oil pressure, which dropped from a normal reading of 70 psi to 20 psi. In response to this indication, the pilot shut down the left engine and feathered the propeller. The pilot then diverted to an alternate airport.
While en route to the alternate airport, the pilot attempted to restart the left engine in an effort to avoid a single-engine landing. However, the pilot reported that the aircraft battery was depleted due to the unsuccessful start attempts. Upon arrival at the airport, the landing gear would not lower via the electrical system because of the low battery output.
The pilot attempted to lower the gear manually but determined there was insufficient time and altitude remaining to complete the operation before landing. Consequently, the pilot attempted a single-engine go-around with the gear partially extended. The aircraft was unable to maintain altitude during this maneuver. The pilot then executed a forced landing in an open field at an elevation of 5600 feet MSL.
The investigation
The investigation focused on the mechanical and operational factors leading to the accident. Examination revealed that the initial trigger was a gradual loss of oil pressure in the left engine. The subsequent chain of events involved the pilot's decision to attempt an in-flight restart, which drained the battery. This depletion prevented the normal electrical operation of the landing gear system.
Findings
Contributing factors included the initial engine oil pressure failure and the resulting battery depletion. The inability to extend the landing gear fully was a direct result of the low battery output caused by the restart attempts. The aircraft's performance during the go-around was insufficient to maintain altitude with one engine inoperative and partial gear extension.
Safety message
This event highlights the critical interdependence of aircraft systems. An initial mechanical failure can cascade into electrical system failures if backup power is exhausted by emergency procedures. Pilots must carefully weigh the risks of attempting restarts against the potential loss of essential electrical power for other critical systems.