On July 23, 1999, approximately 0900 mountain daylight time, a Rockwell International S-2R agricultural spray plane, N3649X, registered to, operated by, and being flown by an airline transport pilot, was substantially damaged during a collision with a fence while executing a forced landing following a loss of power. The pilot sustained minor injuries and no flight plan had been filed. Visual meteorological conditions prevailed. The flight, which was engaged in dispensing fertilizer, was to have been operated under 14CFR137, and had originated from American Falls, Idaho, approximately 0855. The pilot, who was telephonically interviewed by the investigator-in-charge, reported that just before executing a course reversal after his second swath run, he perceived a loss of engine power through a degradation of engine noise and airspeed, but the engine did not completely quit. He further reported that the engine produced no coughing or sputtering. He attempted to correct the condition by activating the boost pump and adjusting the mixture without success. He then jettisoned the 2,400 pound fertilizer load, crossed into another field, made a 20 degree left heading change to avoid a residence, and executed a forced landing. During the landing roll, the aircraft passed through a wooden post fence and the right main landing gear collapsed. This was the second flight of the morning at the same fertilizer load weight, and the outside air temperature was estimated at 55 to 60 degrees Fahrenheit (refer to ATTACHMENT T-I). The pilot later provided a written statement (refer to attached NTSB form 6120.1/2) and reported that "about 1/2 to 2/3 thru [sic] the run I experienced a sudden and near complete loss of power. An attempt was made to regain power by activating the auxiliary fuel pump and placing the mixture into the manual rich [position]. Throttle movement had no response. The spray run was in a uphill direction and some airspeed was converted to additional altitude. After passing the end of the target field the remaining load was jettisoned into some adjacent set aside ground. A crash landing was imminent due to the rough terrain and low altitude. Landing in the rough terrain collapsed the right landing gear and terminated in a violent right turn when the right wing settled into the soft soil of a recently plowed fallow field." The engine was examined on August 25, 1999, at the facilities of Gustin Aviation, Lewiston, Idaho. The examination revealed no evidence of mechanical malfunction. Valve-train continuity was established. Compression of each cylinder was verified, as was the magneto timing. The magnetos were removed and tested with no evidence of malfunction. The oil screen and filters were examined with no blockage noted, and no ferrous particulate material was found within the engine. The engine's air intake system and controls were also checked with no discrepancies reported.