On June 13, 2003, about 2030 Alaska daylight time, a wheel-equipped Longren Centaur L-13 airplane, N4062H, sustained substantial damage when it collided with terrain during takeoff from a private gravel airstrip, about 30 miles east of Chickaloon, Alaska. The airplane was being operated by the pilot as a visual flight rules (VFR) cross country personal flight under Title 14, CFR Part 91, when the accident occurred. The commercial pilot and sole passenger were not injured. Visual meteorological conditions prevailed, and no flight plan was filed. The flight was bound for another airstrip at Chickaloon. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC) on June 14, the pilot said he waited on the gravel airstrip for a thunderstorm and associated rain to pass. He said when he started the takeoff roll, the winds were calm, but during the initial climb, the airplane encountered a downdraft and descended, touching down on a sandbar in a river adjacent to the airstrip. The airplane started to climb again, but was forced down by another downdraft. The pilot said the airplane touched down on another sandbar, and after a third attempt to climb, was forced down into the river where it nosed over. The pilot said there were no preimpact mechanical anomalies with the airplane. In a written statement to the IIC received on June 23, the pilot wrote "in retrospect, it appears there was a mysterious loss of power." He further noted in his written statement that "two witnesses stated there was little or no wind, and that the airplane sounded like a normally powered takeoff, but the sound quickly dwindled, as if the throttle was pulled back to abort the takeoff."