On August 20, 2005, about 1400 Alaska daylight time, a tundra tire-equipped Piper PA-18-150 airplane, N13833, sustained substantial damage when it nosed down during the landing roll on a remote tundra strip, about 80 miles north of Cold Foot, Alaska. The airplane was being operated by the U. S. Fish and Wildlife Service, Anchorage, Alaska, as a visual flight rules (VFR) federal public use law enforcement flight under Title 14, CFR Part 91, when the accident occurred. The solo commercial certificated pilot was not injured. Visual meteorological conditions prevailed, and company flight following procedures were in effect. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge on August 25, the pilot said he landed on an unimproved strip of tundra to check sheep hunters. He said during the landing roll he changed the line of the roll from what he had determined in the air to a line that looked better on the ground. He said his right main wheel hit an "18-inch vertical face," which he had not seen due to low-hanging brush. The right main wheel then hit a hole, and the airplane nosed down. According to the pilot, there were no known mechanical anomalies with the airplane prior to the accident. The operator said the airplane sustained a broken engine mount, and structural damage to the forward fuselage and firewall.