On June 10, 2007, about 1700 Alaska daylight time, a tailwheel-equipped Piper PA-12 airplane, N78492, sustained substantial damage when it nosed over while landing on a mountain ridge, about 41 miles northwest of Koyukuk, Alaska. The airplane was being operated by the pilot as a visual flight rules (VFR) personal cross-country flight under Title 14, CFR Part 91, when the accident occurred. The airline transport certificated pilot received serious injuries, and the sole passenger received minor injuries. Visual meteorological conditions prevailed, and no flight plan was filed. The flight departed the Unalakleet Airport, Unalakleet, Alaska, about 1500. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC) on June 15, the pilot said the mountain ridge where he intended to land looked smooth, free of rocks, and flat on top. He said the ridge sloped upward about 8 degrees, and he intended to land upslope. The pilot said an upslope landing necessitated he land with what he estimated to be about a 5 knot tailwind. According to the pilot, after the main landing gear touched down the airplane rolled into a depression on the ridge, and he believed that rolling into the depression exposed the underside of the tail to the tailwind, which flipped the airplane onto its back. He said there were no preaccident mechanical anomalies with the airplane prior to the accident, and that both wings and the fuselage were damaged during the accident.