On June 1, 1999, at 1200 mountain daylight time, a Snow S2C, N1665S, registered to and operated by Mustang Aviation as a 14 CFR Part 137, aerial application flight, collided with the terrain shortly after takeoff from a private airstrip near Paul, Idaho. Visual meteorological conditions prevailed at the time and no flight plan was filed for the local flight. The airplane was substantially damaged and the commercial pilot, the sole occupant, was not injured. During a telephone interview and subsequent written statement, the pilot reported that this was the seventh flight of the day, and that the load (approximately 1,000 to 1,100 pounds of dry fertilizer), was based on visual volume that had been previously weighed the day before. The pilot reported that he had flown 18 flights the day before under similar temperature conditions (62 degrees F) and load volume without incident. The pilot reported that after the airplane lifted off, he felt that the airplane was not flying as well as it had on the previous flights that day. The pilot stated that he immediately opened the emergency dump which also controls the rate of application. The pilot reported that as he flipped the metal tab out of the way of the dump handle, the tab would not flip clear of the handle because of interference with the seat frame. The pilot reported that at the rate that was set for the application, it would take about three miles to empty the hopper. The pilot reported that he was aware of this problem, but he could hold the stop up with one finger and force the handle around the stop. The pilot reported that he was flying the airplane in ground effect and trying to move the dump handle around the stop, when the airplane collided with a rise in the terrain. The main landing gear contacted the ground first, followed by the left wing. The main landing gear collapsed and the airplane came to rest 90 degrees from the direction of travel, and about 50 yards from the initial impact point. The accident site was about one mile from the end of the airstrip. The pilot stated that if he could have dumped more of the load more quickly, he probably could have flown over the rising terrain. The type certificate data sheet for this aircraft's serial number indicates a gross weight of 4,400 pounds. The pilot reported that he was not aware of the requirement, and had not demonstrated the maximum set gross weight for the conditions to the Federal Aviation Administration per Part 137 certification. A Federal Aviation Administration Inspector from the Boise, Idaho, Flight Standards District Office, responded to the accident site and documented the aircraft's emergency dump system. The inspector reported that the design of the system in the aircraft is different than the manufacturers drawings. At 1153, the Twin Falls airport, located 36 miles west of Paul, was reporting a temperature of 72 degrees F, and 29.81" Hg. The elevation at Twin Falls is 4,151 feet. Utilizing the temperature and pressure altitude from Twin Falls, the density altitude at Paul would have been approximately 6,277 feet. Utilizing the pilot's estimated temperature of 62 degrees, the density altitude would have been approximately 5,684 feet. The elevation at Paul is 4,300 feet.