NTSB Factual Report

On January 3, 2004, at 1240 central standard time, a Pitts S-1S experimental amateur-built airplane, N9AQ, was substantially damaged following the separation of the right main landing gear wheel while landing on a private airstrip near Burleson, Texas. The airplane was registered to and operated by the pilot under Title 14 Code of Federal Regulations Part 91. The private pilot, sole occupant of the airplane, was not injured. The flight departed from the Spinks Airport (FWS) near Fort Worth, Texas with the Rafter J. Airport (3TX9) near Burleson, Texas, as its intended destination. Visual meteorological conditions prevailed, and a flight plan was not filed for the local flight.

The 259-hour pilot, with approximately 17 hours in the accident aircraft, stated that he made a normal approach and landing on the 2,800 feet long by 50 feet wide private turf airstrip. Shortly after ground contact, the right main wheel separated from the aircraft. The right gear strut dug into the grass for approximately 75 feet before the aircraft nosed-over coming to rest in an inverted position. The aircraft sustained damage to the propeller, engine, landing gear, vertical stabilizer, and the upper wing surface.

A witness standing beside the runway, reported that the approach and landing "appeared normal." However, when the right main gear touched the ground, it separated from the aircraft. Afterwards, the right main gear strut drug the nose of the aircraft into the ground and flipped inverted.

According to the FAA Inspector, who responded to the accident site, an old crack was present on the flange where it was welded to the axle nut. A new fracture propagated from both ends of this crack around the lower axle shaft bolt, causing the other 3 remaining bolts to fracture and separate. The FAA Inspector added that the deformity of the flange in the area of the new fracture and the failure of the remaining axle shaft bolts indicated that the gear was subjected to a hard landing and/or substantial side loads prior to, or during the accident landing.

The FAA Inspector also found the separated wheel with a piece of the flange still attached to it by one of the bolts. The flange was able to swivel around the bolt. The Inspector added that this condition suggested that the bolt (and the 3 other bolts) was improperly torqued.

The amateur built Pitts S-1S, serial number 568-H, has accumulated a total airframe time of 1,486.8 hours. The most recent annual inspection was completed on June 22, 2003, 26 hours before the accident. The Lycoming engine, model IO-360-A1B, has 2425.8 hours total time. There has been 247.8 hours since the engine's last overhaul.

NTSB Probable Cause

The separation of the right main gear wheel, during landing, due to the improper maintenance by unknown maintenance personnel on the right main landing gear assembly.