What happened
While conducting a survey operation at an altitude of 400 feet AGL, the crew of a C-47 identified what appeared to be an oil leak originating from the number two engine. In response to this perceived issue, the propeller on the second engine was feathered. To compensate for the loss of power, the pilot increased the power setting on the number one engine.
During this adjustment, the propeller on the first engine entered a runaway state, creating significant aerodynamic drag. The crew attempted to unfeather the number two engine to restore operational power, but these efforts were unsuccessful. Consequently, the C-47 impacted the ground.
Findings
Investigations into the accident suggest that the decision to feather the right engine was performed too hastily given the aircraft's low altitude of only 400 feet. Furthermore, the increase in power to the left engine led to an uncontrollable propeller state, which may have been caused by a failure within the propeller governor or a deficiency in the oil strainer screen. This sequence of events necessitated the feathering of the remaining functional engine, leaving the aircraft with no available power and resulting in an immediate forced landing.