On July 21, 1997, at 1830 Alaska daylight time, a Cessna 208 airplane, N9481F, sustained substantial damage when it departed the runway at the Naknek-Tibbetts Airport, Naknek, Alaska, and impacted trees. The airline transport certificated pilot and two passengers were not injured. The airplane was operated by Peninsula Airways, Inc., of Anchorage, Alaska, as scheduled commuter flight number 354 from King Salmon, Alaska to Naknek. The flight was conducted under 14 CFR Part 135, a company VFR flight plan was filed, and visual meteorological conditions prevailed at the time of the accident. The airplane departed the Naknek Airport at 1825, and was en route to the Tibbetts Airport, which is separated from the Naknek Airport by a drainage ditch. The flight immediately entered the pattern to land at the Tibbetts Airport. The pilot reported heavy rain began while maneuvering to land, and that he lost forward visibility while on short final. After landing, the airplane drifted off the right side of the 1,700 foot long by 50 foot wide runway, and contacted trees.