"THIS CASE WAS MODIFIED MARCH 25, 2009." On March 22, 2008, approximately 0930 Pacific daylight time, a Gulfstream-Schweizer G-164B, N8148K, was substantially damaged during landing following the partial separation of its rudder, while in-flight, near Genesee, Idaho. The commercial pilot, the sole occupant in the airplane, sustained a minor injury. Heimgartner Aviation LLC, was operating the airplane under 14 CFR Part 137. The airplane was on an aerial application sortie when the rudder failed; it had departed a private airstrip at approximately 0900. Visual meteorological conditions prevailed for the local flight; a flight plan had not been filed. The pilot said that a few minutes after takeoff, he lost rudder control. He flew the airplane for approximately 1/2 hour to learn its flight characteristics at low airspeed and low power setting. During the landing, the airplane turned sideways, nosed over, and came to rest inverted. Examination of the airplane by Federal Aviation Administration (FAA) inspectors revealed that the lower rudder attachment point had failed and the separation surfaces displayed evidence of severe corrosion. The airplane had an annual inspection on March 17, 2008, and the airplane had flown 1/2 hour since the inspection. On December 19, 2008, the FAA issued Airworthiness Directive (AD) 2008-22-21, which expanded the applicability of a previous AD 78-08-09 to include all G-164 series airplanes. The previous AD did not include the accident airplane. The expanded AD requires repetitive inspections of the rudder main tubular spar for corrosion and correction if detected. Prior to this AD, the area where the corrosion was found and failure occurred did not require inspection.