On December 12, 1956, a Curtiss C-46 Commando (registration N1662M) operated by ASA International Airlines - Aerovias Sud Americana was involved in an aviation accident near San Miguel, Panama during takeoff. No fatalities were reported. Investigators recorded the probable cause as: The left engine experienced an overspeed condition that could not be mitigated through standard emergency shutdown procedures. This summary draws on records from the Bureau of Aircraft Accidents Archives (B3A).
An aircraft experienced a left engine overspeed shortly after departing San Miguel Island, resulting in an emergency sea landing and the loss of the airframe.
What happened
During the initial climb phase following departure from San Miguel Island, the aircraft's left engine experienced an overspeed condition. In response to the malfunction, the crew attempted to feather the propeller and shut down the affected engine; however, these emergency procedures were unsuccessful.
As the aircraft lost both airspeed and altitude, the pilots performed an emergency ditching in the ocean a few kilometers from the coastline. While both pilots were successfully rescued from the scene, the aircraft subsequently sank to a depth of 35 meters approximately 30 minutes after the incident.
Findings
The primary issue was an engine overspeed on the left side of the aircraft.
The crew's attempts to mitigate the failure by feathering the propeller and shutting down the engine were not successful.
Probable cause
The left engine experienced an overspeed condition that could not be mitigated through standard emergency shutdown procedures.