Approach and Descent
The pilot was conducting an instrument flight rules (IFR) flight and received clearance from the controller for a VOR runway 22 approach at the destination airport. During the descent, the pilot did not apply carburetor heat. The aircraft's Let-Down procedures checklist states, "Carburetor Heat - AS REQUIRED to prevent carburetor icing."
Power Loss at Minimum Descent Altitude
Upon reaching the minimum descent altitude (MDA) for the approach, the pilot advanced the throttle but did not obtain an engine response. Recognizing that the runway could not be reached, the pilot executed a forced landing into a river.
Weather Conditions
The surface weather observation at the destination airport reported a temperature of 75 degrees Fahrenheit and a dew point temperature of 61 degrees Fahrenheit. Review of the Department of Transportation Icing Probability Chart indicates that under these conditions, an aircraft at glide power would encounter serious icing conditions.
Engine Examination
Following the incident, the engine was mounted in a test stand and connected to an alternate fuel and battery source. Engine controls and magneto grounding wires were installed, and the mixture control was safetied in the full rich position. The engine was started and ran at idle power. After warm-up, the throttle was advanced to full power, and the engine stabilized at a takeoff rpm of 2,000. The throttle was then returned to idle, the safety wire on the mixture was cut, and the engine was shut down using the mixture control.