On March 31, 1999, at 1715 central standard time, an Air Tractor AT-301 agricultural airplane, N8789S, was substantially damaged upon collision with a post following a loss of control while landing near Garwood, Texas. The instrument rated commercial pilot, sole occupant of the airplane, was not injured. The airplane was registered to and operated by A.N.F. Air Service Inc., of Garwood, Texas. Visual meteorological conditions prevailed for the Title 14 CFR Part 137 aerial application flight for which a flight plan was not filed. The local flight originated from the operator's private airstrip approximately 30 minutes prior to the accident. The pilot reported that he departed the 2,600 foot airstrip with a load of herbicide to be sprayed on a rice field approximately 2 miles southwest of the airstrip. After dispensing his load, the pilot returned to the airstrip for a landing on runway 35. The operator reported to the FAA inspector, who responded to the accident site, that after a normal landing and roll out, the pilot initially applied brake pressure to slow down the airplane's landing roll. The pilot reported that when he attempted to re-apply brake pressure, the right brake pedal "fell all the way to the floorboard." The pilot added that the airplane made a gradual left turn, which he could not compensate for with an inoperative right brake. The airplane came to a stop after the left wing impacted a concrete pole located on the west side of the airstrip. Examination of the airplane by the FAA inspector revealed structural damage to the left wing spar and the empennage. The inspector stated that the failure of the right brake was due to the eye bolt, which connects the brake master cylinder to the top portion of the rudder pedal, pulling out of the master cylinder. The inspector added that the eye bolt's jam nut was found still attached to the shaft of the rod end. The operator stated that the only possible way for the eye bolt to become separated from the master cylinder was for the eye bolt to pull out of the threaded hole in the brake master cylinder. The operator further stated that the time in service for the brake master cylinder was unknown. He added that the bottom 2 or 3 threads of the eye bolt appeared to be damaged or stripped, which "could have resulted in the eye bolt pulling out" of the master cylinder. The failed part (eye bolt, master cylinder attach) was manufactured by Parker Hannifin (formerly Cleveland) and assigned an Air Tractor part number 40002-1. The brake master cylinder was manufactured by Cleveland as part number 10-23A. The operator reported in the enclosed NTSB Form 6120.1/2 that the last annual inspection on the airplane was completed 23 hours prior to the accident. The failed components were not available for further metallurgical examination.