Incident
During an aerial pipeline patrol flight, the aircraft was in cruise flight at an altitude of 500 feet above ground level when it experienced a power loss. The pilot executed an off-airport emergency landing in rough terrain, which resulted in substantial damage to the aircraft. The pilot and passenger reported that earlier on the same flight, prior to the emergency landing, they had encountered a power loss that was alleviated by the application of carburetor heat.
Investigation
The subsequent investigation focused on the carburetor heat system. It was discovered that the carburetor heat gate valve would only close approximately two-thirds of the way when the control was placed in the carburetor heat full-on position. Further examination revealed that the actuator arm was binding against the interior baffling of the engine compartment. This binding prevented the valve from closing fully, potentially affecting engine operation.
Findings
The mechanical interference between the actuator arm and engine compartment baffling restricted the movement of the carburetor heat gate valve. This condition could lead to improper carburetor heat control, affecting engine performance during critical phases of flight. The exact cause of the power loss was not explicitly stated, but the carburetor heat valve issue was identified as a significant factor in the incident.