NTSB Factual Report

On March 29, 2002, about 1900 Alaska standard time, a wheel-equipped Interstate Arctic Tern airplane, N48027, sustained substantial damage during a forced landing about five miles southwest of Big Lake, Alaska. The airplane was being operated by the pilot 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. Visual meteorological conditions prevailed, and no flight plan was filed. The flight originated at Merrill Field, Anchorage, Alaska, about 1800, with a stop at Goose Bay, Alaska.

During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), on March 29, the pilot said he departed Goose Bay, en route to Merrill Field. He said he was less then half-way to Merrill Field when the cockpit started to fill with smoke, so he turned toward Goose Bay. En route the engine started to lose power, and he decided to make an emergency landing on a snow-covered field. Prior to landing the engine lost all power. When the airplane touched down on the field, the main landing gear broke through the crusted snow, and the airplane nosed over.

During a telephone conversation with the IIC on April 1, the pilot said he found a broken weld on the airplane's engine tailpipe. The hot exhaust gasses escaping from the tailpipe into the engine compartment burned wiring and hoses in the compartment. He said there were no known mechanical problems with the airplane prior to the accident.

The NTSB IIC inspected the airplane on April 8, and noted that the engine exhaust stack had separated from the cabin heater's heat exchanger. The pilot said the exhaust stack was missing when he landed. The hot exhaust gasses burned a hole through the lower engine cowling. There was a large burned area on both the interior and exterior of the lower engine cowling. All of the electrical wiring, below the level of the engine cylinders, was burned. The alternate air and heater air hoses/ducts were burned away. The paint on the lower portion, of the right side of the fuselage, aft of the lower engine cowling, was blistered. The belly of the airplane was covered with a thin layer of soot. The throttle cable, mixture cable, and fuel line were charred. The wing lift strut attachment points exhibited stress tearing of the fabric around the attachment points. The lift struts were bent. The fabric on the top of the fuselage showed stress fractures and tearing, and the top of the vertical fin was crushed. One blade of the two bladed, fixed-pitch propeller was bent rearward at the tip about 11/2 inches.

NTSB Probable Cause

The separation of the exhaust system stack from the heat exchanger. A factor associated with the accident was an engine compartment fire.