On July 6, 2002, at 0930 Pacific daylight time, a Grumman-Schweizer G-164B agricultural airplane, N3631B, sustained substantial damage when it impacted terrain near Sacramento, California. The commercial pilot, sole occupant of the airplane, was not injured. The airplane was registered to and operated by Farm Air Flying Service, Sacramento, California, under 14 CFR Part 137. Visual meteorological conditions prevailed for the local aerial application flight, and a flight plan was not filed. The flight originated from a private airstrip near Sacramento at 0928. As reported in the Pilot/Operator Aircraft Accident Report (NTSB form 6120.1/2), the pilot had been applying fertilizer for about 2 hours. After taking off with a 2,000 pound load and initiating a left turn at an altitude of approximately 15 feet agl, the pilot reported hearing a "loud bang and a sharp jolt as the airplane began shaking violently." The pilot stated that he leveled the wings and reduced power; "however, the vibration did not subside." He then initiated a shallow right turn in order to land on a road. "As I began to maneuver for landing I saw a burst of flame from the exhaust and heard the engine quit and felt the aircraft settle." The airplane impacted a levee and flipped over, coming to rest inverted. It was reported by the operator that both wing spars, the rudder, and vertical stabilizer had sustained structural damage. Both main landing gear and the engine had separated from the airplane. During post-accident investigation of the wreckage, it was noted that the outboard section of one propeller blade was missing. The inboard section of the Hamilton Standard propeller blade, P/N AG200-2 Chg B, S/N 76500, was sent to the NTSB Materials Laboratory Division, Washington, D.C., for examination. The Senior Metallurgist reported the blade was fractured approximately 26 to 27 inches from the butt end. Optical examination of the fracture face found features consistent with fatigue progression over the majority of the fracture. Closer examinations revealed beach marks and other progression features indicating fatigue initiation at a mechanical dent on the camber surface near midspan. Further examination indicated that fatigue accounted for approximately 70% of the total fracture area. Refer to attachment, Report No. 02-103.