On September 2, 1998, about 1002 Alaska daylight time, an amphibious Grumman G-44 airplane, N139F, sustained substantial damage during a collision with mountainous terrain, about 80 miles north of Dillingham, Alaska. The airplane was being operated as a visual flight rules (VFR) on-demand passenger flight under Title 14, CFR Part 135, when the accident occurred. The airplane was operated by Fresh Water Adventures, Inc., Dillingham. The certificated commercial pilot, and the two passengers aboard were not injured. Instrument meteorological conditions prevailed at the time of departure, and company flight following procedures were in effect. The flight originated at the Dillingham Airport, about 0840, under special VFR weather conditions. During a telephone conversation with the National Transportation Safety Board investigator-in-charge on September 2, the pilot reported that he was transporting two hunters to a remote lake located about 100 miles north of Dillingham. During the flight, low clouds, rain, and fog were present in an area of mountainous terrain along the route of flight. The pilot stated that he intended to utilize a narrow mountain pass to transit the area, and as he entered the mountain pass, discovered that the ceiling and visibility would not allow safe passage. He said that he made an emergency 180 degree turn in an attempt to exit the pass, and subsequently collided with terrain. After initial impact, the airplane slid downhill about 100 feet, and came to rest on a 35 degree slope. The airplane sustained substantial damage to the fuselage, wings, and elevator. The pilot stated that weather conditions at the time of the accident consisted of: Ceiling, 500 foot overcast; visibility, 2 miles with rain and fog; wind 360 degrees, at 8 knots. The closest official weather observation station is Dillingham, located about 80 nautical miles southeast of the accident site. On September 2, 1998, at 0925, an Aviation Routine Weather Report (METAR) was reporting, in part: Wind, 330 degrees at 6 knots; visibility, 3 statute miles with light rain and mist; clouds, 500 feet broken, 800 feet overcast; temperature, 48 degrees F; dew point, 48 degrees F; altimeter, 29.34 inHg. The pilot noted that there were no preaccident anomalies with the airplane.