NTSB Factual Report

HISTORY OF FLIGHT

On June 1, 2002, about 1110 Alaska daylight time, a Piper PA-18-150, N6969H, sustained substantial damage during an emergency landing about one and one-half miles west of Merrill Field, Anchorage, Alaska. The airplane was being operated as a visual flight rules (VFR) personal flight under Title 14, CFR Part 91, when the accident occurred. The solo private pilot was not injured. The accident airplane departed Merrill Field about 1100 en route to Wasilla, Alaska, by way of Goose Bay, Alaska. Visual meteorological conditions prevailed at the time of the accident, and no flight plan was filed.

During an interview with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC) at the accident site on June 1, the pilot said the airplane was at 600 feet msl crossing the channel west of Anchorage when he noticed a decline in engine rpm. He said the airplane was configured for cruise flight and he was mid-channel. He said he applied carburetor heat, and switched from the right wing fuel tank to the left wing fuel tank. He said after he applied carburetor heat, and switched fuel tanks the rpm increased momentarily, and then the engine quit. He said he turned east and headed for the shoreline, and selected an open dirt area adjacent to a fuel storage depot for landing.

The pilot said during the preflight inspection the right fuel tank appeared to be about three-quarters full. He said he could not tell how much fuel was in the left fuel tank, but he believed there was at least a couple of gallons, and that he had "sumped" both fuel tank drains during the inspection. He said there was a magneto problem during the engine run-up, but leaning the mixture cleared up the problem. Due to airport traffic, the ground run for the engine was about 15 minutes from startup to takeoff. The climb-out and transition to cruise flight were normal.

PERSONNEL INFORMATION

The pilot held a private pilot certificate with a FAA rating for single-engine land airplane. The pilot was issued an FAA second class medical certificate on September 22, 2001. According to information received from the pilot, he had accumulated 92.5 total flying hours, 4.8 of which were in the make and model of the accident airplane.

AIRPLANE INFORMATION

The airplane was a Piper PA-18-150 with oversize tires, and a Lycoming O-320-A2B, carbureted engine. The airframe had accumulated 5651 hours total time since new, and the engine had accumulated 1555 hours total since overhaul. The fuel system was unmodified, and had three positions available on the fuel selector; right or left wing main fuel tanks, or "off."

METEOROLOGICAL INFORMATION

The closest official weather observation station is Merrill Field, which is located one and one half miles east of the accident site. At 1053, an Aviation Routine Weather Report (METAR) was reporting in part: wind, 310 degrees (true) at 4 knots; visibility, 10 statute miles in light rain; cloud and sky condition, few at 1,200 feet, 2,200 feet broken, 4,700 feet overcast; temperature, 48 degrees F; dew point, 45 degrees F; altimeter, 29.92 inHg. The pilot reported flying through light rain at the time the airplane lost engine power.

WRECKAGE INFORMATION

During the emergency landing at a fuel storage depot near the port of Anchorage, the airplane impacted near the top of a 4 feet high dirt berm. During the impact the left main landing gear collapsed. The airplane rolled/skidded across the top of the berm, and as it descended the opposite side of the berm, it nosed over. The airplane sustained damage to both wings, the left wing lift-struts, vertical stabilizer, and main landing gear.

The airplane was inspected on-site by the NTSB IIC. The airplane was on its back, and emergency workers had placed a rubber fuel containment dam under the right wing fuel filler cap, to capture fuel leaking from the right wing tank. The left wing fuel tank was not leaking. The left wing fuel sight gauge showed no signs of fuel in the left wing tank. The left wing was removed from the airplane during the recovery operation, and no evidence of fuel was found in the left wing tank. During the removal of the right wing, about nine gallons of fuel were removed. The left main wing tank was selected on the fuel selector valve.

The engine appeared to be intact, and the propeller showed no chord-wise scratching, or leading edge gouging. One blade of the two-bladed propeller was bent rearward.

ADDITIONAL INFORMATION

The airplane was taken to a maintenance hangar at Merrill Field for further examination and testing. The propeller was replaced, and a fuel supply was connected to the engine. The engine was started and run through various power settings without faltering.

The pilot described the weather conditions as 1,000 to 1,500 feet overcast; temperature, mid to high 40's; visibility, greater than 3 miles in light rain showers. He also stated his first indication of a problem was the loss of engine rpm. To counter the loss of engine rpm the pilot said he applied carburetor heat, and switched from the right wing fuel tank to the left wing fuel tank.

According to the FAA's, Aviation Weather for Pilots and Flight Operations Personnel, Advisory Circular 00-6A, the amount of water vapor in the air is measured by either relative humidity, or the dew point temperature. Relative humidity expresses the actual water vapor present at a given temperature. One hundred percent relative humidity means the air is saturated. For air that is less then one hundred percent saturated, the dew point is the temperature to which the air must cool to become one hundred percent saturated.

According to the FAA's, INDUCTION ICING - PILOT PRECAUTIONS AND PROCEDURES, Advisory Circular 60-9, 7. INDICATIONS OF INDUCTION ICING, reads, in part: "The possibility of induction icing should always be considered when the temperature is between 32 and 70 degrees F with a relative humidity greater then 50 percent, or when the temperature is below freezing with visible moisture in the air. The effect of induction icing is a gradual, progressive decline in power delivered by the engine. With a fixed pitch propeller this is evidenced by a loss in engine rpm and ... ."

According to a carburetor icing probability chart, the atmospheric conditions at the time of the accident reflected the probability of serious icing at any power setting (see attached chart).

The Piper PA-18 Operators Manual does not have a specific emergency procedures section. It does have Section VII, which explains the fuel system. Section VII reads, in part: "In the two tank system, it is recommended that the left tank be considered the main tank and that fuel be used from the right tank first on long flights, saving the left tank until last." Under 'OPERATING INSTRUCTIONS', specifically 'WARM UP AND GROUND CHECK' the manual reads, in part: "Carburetor heat should be checked during warm up to make sure the heat control operation is satisfactory and to clear out the engine if any ice has formed. It should also be checked in flight occasionally when outside air temperatures are between 20 and 70 degrees F to see if icing is occurring in the carburetor."

NTSB Probable Cause

The pilot's selection of a fuel tank that did not contain a usable quantity of fuel. Factors associated with the accident are the dirt berm, meteorological conditions conducive to carburetor icing, and carburetor ice.