On June 6, 2004, about 1100 Alaska daylight time, a tundra tire-equipped Cessna 170B airplane, N2631D, sustained substantial damage when it nosed over while landing on soft terrain, about 8 miles west of Dillingham, Alaska. The airplane was being operated as a visual flight rules (VFR) local area 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, was not injured. Visual meteorological conditions prevailed. 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 June 6, the pilot reported that he was planning to test a remote tundra-covered area for its suitability as a landing strip. The area was about 2,000 feet square adjacent to the Snake River. The pilot said he configured the airplane with 20 degrees of flaps, and touched the main landing gear tires on the tundra to test the surface. The tires dug into the soft tundra and the airplane nosed over. The airplane received damage to the propeller, fuselage, vertical stabilizer, and the rudder.