On February 29, 2004 about 1200 Alaska standard time, a ski-equipped Piper PA-15 airplane, N4492H, sustained substantial damage when it collided with trees during an emergency landing, about 18 miles west of Big Lake, Alaska. The airplane was being operated as a visual flight rules (VFR) cross-country personal flight under Title 14, CFR Part 91, when the accident occurred. The airplane was operated by the pilot. The private certificated pilot, the sole occupant, received minor injuries. Visual meteorological conditions prevailed. The flight originated about 1130 from a cabin on a small frozen lake, about 5 miles west-northwest of Skwentna, Alaska, and was en route to Merrill Field, Anchorage, Alaska. 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 March 1, and during an interview on March 8, the pilot reported that after departure from his cabin, he observed areas of sleet near Beluga Mountain. He deviated east of his normal route of flight around areas of low visibility by following the Skwentna River to the Yentna River. While in cruise flight, about 1,200 feet msl, or about 800 feet agl, the pilot said the airplane began a gentle, uncommanded left turn. He applied right aileron control in an attempt to straighten the airplane, but there was no change, and the airplane's left bank became increasingly steep. The pilot applied right rudder to prevent the airplane from becoming inverted. He said the airplane was in a left descending spiral, and he decided to land as soon as possible. He selected an emergency landing area on a small frozen lake, but was unable to achieve his selected spot. He then selected a stand of trees, and during the landing, the airplane's wings, landing gear, and fuselage received extensive damage. The pilot said that the entire emergency event lasted about one minute. The pilot indicated that he made a radio call to an over-flying aircraft to report the accident, but he was unsure of his exact position. No emergency locator transmitter (ELT) was installed in the airplane. The pilot was reported overdue by relatives on February 29, at 2034. Search personnel located the accident site on March 1, about 0830. The closest official weather observation station to the accident location is Skwentna, which is about 26 nautical miles west of the accident site. At 1150, an Aviation Routine Weather Report (METAR) was reporting, in part: Wind, 330 degrees (true) at 4 knots; visibility, 1.5 statute miles in light snow and mist; clouds and sky condition, 1,000 feet broken, 1,800 feet overcast; temperature, 30 degrees F; dew point, 29 degrees F; altimeter, 30.27 inHg. The pilot reported that in the area of the accident, he was flying under 2,000 foot overcast to broken sky conditions, with calm wind conditions. He said the visibility was VFR with low visibility to the south of his position, but clear toward the southeast. The pilot indicated that the airplane was rebuilt, and had an annual inspection in September, 2003. Since the inspection, the airplane had accrued about 2 hours of operation. The pilot also said that airplane skis were installed on the airplane just prior to the accident flight. The installation date was not recorded in the airplane maintenance logs. The airplane was disassembled and recovered from the accident site by friends of the pilot. The wings, ailerons, horizontal stabilizers, elevators, and the rudder, were stored at the home of the pilot. The fuselage was recovered and stored at the pilot's parking spot at Merrill Field. On March 19, the airplane fuselage and components were examined by NTSB and FAA personnel. No evidence of a flight control system malfunction was found. The ski retention cables and springs exhibited no anomalies.