ANC04LA031

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.

On February 9, 2004, about 1845 Alaska standard time, a wheel-equipped Cessna 182M airplane, N71886, sustained substantial damage when it collided with a ditch during a forced landing shortly after takeoff from the Yakutat Airport, Yakutat, Alaska. The airplane was being operated as a visual flight rules (VFR) cross-country business flight under Title 14, CFR Part 91, when the accident occurred. The airplane was operated by the pilot. The airline transport certificated pilot, the sole occupant, was not injured. Night visual meteorological conditions prevailed. No flight plan was filed, nor was one required.

During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), on February 10, the pilot reported that he stopped in Yakutat for fuel on his cross-country flight to Anchorage, Alaska. After fueling, the pilot said he drained the fuel system sumps and found no contaminants. He performed an engine run-up, and then departed on runway 29. After takeoff, about 400 feet above the ground, the pilot indicated that the engine began to run rough and slowly lose power. He switched fuel tanks and applied carburetor heat, but the engine power continued to decline, and the airplane lost altitude. The pilot 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 came to rest about 1,000 feet beyond the departure end of runway 29, and received structural damage to the left wing and fuselage. The left main landing gear was also torn off the airplane.

On February 13, a Federal Aviation Administration (FAA) aviation safety inspector from the Juneau, Alaska, Flight Standard District Office (FSDO), examined the airplane in Yakutat after it was retrieved from the ditch. His examination revealed that the fuel, air intake, exhaust, and ignition systems were intact at the time of the accident. The fuel tanks, gascolator, and carburetor bowl contained fuel that was free of contaminants. The spark plugs were sooted.

At 1853, an Aviation Routine Weather Report (METAR) from Yakutat was reporting, in part: Wind, 070 degrees at 7 knots; visibility, 10 statute miles; clouds and sky condition, 11,000 feet overcast; temperature, 37 degrees F (+3 degrees celsius); dew point, 31 degrees F (-1 degree celsius); altimeter, 30.16 inHg.

The FAA's Advisory Circular (AC) 61-23C, Pilot's Handbook of Aeronautical Knowledge, Chapter 2, Carburetor Icing, states, in part: "... if the temperature is between -7 degrees C (20 degrees F) and 21 degrees C (70 degrees F), 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. For airplanes with fixed-pitch propellers, the first indication of carburetor icing is loss of RPM. For airplanes with controllable pitch (constant-speed) propellers, the first indication is usually a drop in manifold pressure. In both cases, a roughness in engine operation may develop later."

The FAA's AC 20-113, Pilot Precautions and Procedures to be Taken in Preventing Aircraft Reciprocating Engine Induction System and Fuel System Icing Problems, 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."

According to the FAA inspector who examined the airplane, it was equipped with a carburetor air temperature gauge. The airplane's Owner's Manual, Optional Systems, Carburetor Air Temperature Gage, states, in part: "A carburetor air temperature gage may be installed in the airplane to help detect carburetor icing conditions. The gage is 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..."