On August 30, 1999, at 1845 central daylight time, a Cessna A188B agricultural airplane, N731JY, nosed over during landing at a private airstrip near Seminole, Texas. The aircraft was owned and operated by Addison Flying Service, Seminole, Texas, under 14 Code of Federal Regulations Part 137. The commercial pilot received serious injuries, and the aircraft sustained substantial damage. Visual meteorological conditions prevailed for the flight, and a flight plan was not filed. The flight originated from Kilgore, Texas, with a landing at the Seminole/Gaines County Municipal Airport. The flight then departed this municipal airport for a positioning flight to the nearby private airstrip at 1830. During a telephone interview, conducted by the NTSB investgator-in-charge (IIC), the operator reported that the aircraft was landing to the east on his private caliche (gravel) runway (5,280 feet long and 60 feet wide). The airplane departed the right side of the runway into soft dirt and "flipped" to the inverted position. The vertical stabilizer and rudder were crushed. The cockpit was compressed and the wings were wrinkled. On the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1/2) the pilot stated that "after initial touchdown the pilot seat slid back all the way which made it impossible to reach the left rudder pedal." The pilot further stated that his left leg is shorter than his right leg. The FAA inspector, who responded to the site, found that the pilot seat was dislodged from the seat track. Further examination revealed that the "part number 0700645-1 housing assembly seat roller forward left had spread open to near the width of the seat rail allowing the seat to dislodge from the locked position." The FAA inspector reported that the "airworthiness directive 87-20-03 had not been properly accomplished on the seat installation in N731JY. The seat did not meet the locking pin engagement requirements of the airworthiness directive. The airworthiness directive had been properly signed off in the maintenance records during the last inspection." The aircraft tachometer reading was 249.4 hours. A review of the maintenance records by the NTSB investigator-in-charge revealed that the last annual inspection was performed on April 16, 1999, at a total aircraft time of 5,039 hours, and the tachometer was replaced at that time.