Incident Summary
An airline transport certificated pilot stopped for fuel during a night cross-country flight. After refueling, the pilot reported draining the fuel system sumps and finding no contaminants. He performed an engine run-up before departing. Shortly after takeoff, at approximately 400 feet above ground level, the engine began to run rough and slowly lose power.
Emergency Landing and Damage
The pilot switched fuel tanks and applied carburetor heat, but engine power continued to decline, causing the aircraft to lose altitude. He executed a 180-degree left turn toward the airport and made an emergency off-airport landing. During the landing, the airplane collided with a ditch, resulting in structural damage to the left wing, fuselage, and landing gear.
Postaccident Examination
A postaccident examination of the engine found that the spark plugs were sooted. No other mechanical malfunctions were identified.
Weather and Carburetor Icing Considerations
At the time of the accident, the temperature was 37°F (3°C), and the dew point was 31°F (-1°C). FAA Advisory Circular (AC) 61-23C notes that carburetor ice can form when temperatures are between -7°C and 21°C in conditions of visible moisture or high humidity, particularly at low or closed throttle settings. AC 20-113 states that vaporization icing may occur at temperatures from 32°F to 100°F with relative humidity of 50% or above; a temperature/dew point spread of 20°F or less indicates potential icing conditions. The airplane was equipped with a carburetor air temperature gauge marked with a yellow arc between -15°C and +5°C, indicating the range where carburetor icing can occur.