Yakutat Airport
Aircraft Accident/Incident Report

Yakutat, Alaska 99689
Monday, February 9, 2004 18:45 AST

The airline transport certificated pilot stopped for fuel on a night cross-country flight. After fueling, the pilot said he drained the fuel system sumps and found no contaminants. He performed an engine run-up, and then departed. After takeoff, about 400 feet above the ground, the engine began to run rough and slowly lose power. The pilot switched fuel tanks and applied carburetor heat, but engine power continued to decline, and the airplane lost altitude. He made a 180 degree left turn toward the airport and made an emergency, off-airport landing, during which the airplane collided with a ditch. The airplane received structural damage to the left wing, fuselage, and landing gear. A postaccident examination of the airplane's engine revealed that the spark plugs were sooted, and no other mechanical malfunction was found. At the time of accident, the temperature was 37 degrees F (+3 degrees C), and the dew point was 31 degrees F (-1 degree C). FAA Advisory Circular (AC) 61-23C, states, in part: "... if the temperature is between -7 degrees C and 21 degrees, with visible moisture or high humidity, the pilot should be constantly on the alert for carburetor ice. During low or closed throttle setting, an engine is particularly susceptible to carburetor icing. AC 20-113, states, in part: "Vaporization icing may occur at temperatures from 32 degrees F to as high as 100 degrees F with a relative humidity of 50 percent or above... Since aviation weather reports normally include air temperature and dew point temperature, it is possible to relate the temperature/dew point spread to relative humidity. As the spread becomes less, relative humidity increases and becomes 100 percent when temperature and dew point are the same. In general, when the temperature/dew point spread reaches 20 degrees or less, you have a relative humidity of 50 percent or higher and are in potential icing conditions." The airplane was equipped with a carburetor air temperature gauge that was marked with a yellow arc between -15 degrees to +5 degrees celsius. The yellow arc indicates the carburetor temperature range where carburetor icing can occur.

The pilot's delayed use of carburetor heat, which resulted in an engine power loss during takeoff-initial climb, a forced landing, and subsequent collision with terrain. A factor contributing to the accident was the presence of carburetor icing conditions.