On June 12, 2003, approximately 0800 Pacific daylight time, a Rockwell International S-2R, N8468V, impacted a post during an aerial application flight near Royal City, Washington. The pilot was not injured, but the aircraft, which is owned and operated by Royal City Flying service, sustained substantial damage. The 14 CFR Part 137 aerial application flight, which departed a local airstrip about 15 minutes earlier, was being operated in visual meteorological conditions. According to the pilot, while applying chemicals to a field, the aircraft's right main landing gear impacted a 20 foot high post. The pilot then dispersed the remainder of his load and returned to the strip he was using as his base of operations. Knowing that the right gear had been damaged, the pilot held the right wing higher than the left as long as he could during the landing roll, but when the right main gear touched the landing surface it collapsed. When the gear collapsed, the right wing came in contact with the terrain, resulting in substantial damage to the right wing main spar.