On January 8, 2000, at 1034 hours Pacific standard time, a homebuilt Pitts S1X, N900SH, collided with terrain while performing an aerobatic routine at an airshow at the Cable Airport, Upland, California. The experimental airplane, owned and operated by the pilot, was destroyed. The commercial pilot was fatally injured. The local airshow performance, conducted under 14 CFR Part 91, had originated at the Cable Airport at an unspecified time. Visual meteorological conditions prevailed and no flight plan was filed. According to witnesses, the pilot was performing an aerobatic routine with two other airplanes, known as a "squirrel cage" maneuver. The airplanes would take turns entering the aerobatic box to perform a single choreographed maneuver. The airshow held a waiver for an "airshow box" (performing area), which was partly over a rock quarry. The routine card indicated that the pilot was supposed to perform multiple snap rolls when the accident occurred. A video of the pilot's routine was provided to the Safety Board. A frame-by-frame examination was conducted, with the assistance of the International Aerobatic Club. The video showed that the pilot made 3 1/2 snap rolls to the right, then 2 1/2 spins to the left. The elevator appeared to be loaded. The video cut out as the pilot impacted the rock quarry. Witnesses reported that there was a fire on impact. No one on the ground was injured. According to the Federal Aviation Administration (FAA) airman certification database, the pilot held an airline transport pilot certificate with an airplane multiengine land rating. He also held a commercial pilot certificate with an airplane single engine land rating and a private certificate with a helicopter rating. The FAA aeromedical certification database revealed that the pilot held a second-class medical, issued March 11, 1999, with the restriction that the pilot must wear corrective lenses. The aircraft was examined following its recovery from the impact site. The flight controls were inspected. Both rudder pedals remained secured at their respective fittings. Both rudder cables were fractured approximately midspan. The fractured cables displayed frayed ends, and "necking" was evident when viewed under a magnifying lens. The elevator trim was intact and secure at its fitting. The elevator control system was separated at a joint fitting. It remained connected forward of the stick to just aft of the seat. Both the right and left side top and bottom ailerons both moved freely with no noted binding. The right side aileron control system was fractured at the bellcrank joint. The left side aileron control system was fractured at a joint fitting. No foreign objects were found in any of the control system surfaces. All controls could be manipulated freely by hand. Examination of the engine revealed significant thermal damage. The propeller could not be rotated by hand. The top and bottom spark plugs were removed and examined. They exhibited normal coloration and wear patterns consistent with the Champion Check-A-Plug chart. The magnetos, fuel pump, and sections of the fuel injection servo displayed significant damage and no testing was conducted. The cylinders were internally examined utilizing a lighted bore scope; they appeared undamaged. The valves were intact and there was no evidence of foreign object ingestion or oil residue. The fuel injector(s) remained at their respective locations with the fuel lines attached. The rocker box covers were removed. The rocker assemblies, springs, and valve retainers were secure at each cylinder assembly. There was no evidence of metal contamination observed at the rockers or oil screen. The oil cooler bypass valve (vernatherm) remained intact. The fuel injection servo fuel inlet screen was removed and displayed no visible contaminants. The oil sump and portions of the accessory case had been displaced, exposing portions of the crankshaft and accessory gears. Visual inspection of the internal components through those voids utilizing a lighted bore scope revealed no evidence of malfunction. There was no evidence of mechanical malfunction. According to the pilot's ACE, the pilot had not been approved for squirrel cage maneuvers. The pilot held a "level 3" certificate, and according to the ACE, at level 3, any deviations from the planned routine should be approved. He had only approved the pilot for his usual routine.