Tuesday, December 20, 2011
Air Race Accidents
Safety in air racing depends on the airplane as well as the pilot
On September 6, 2008, an amateur-built single-seat Cassutt racing aircraft crashed after an in-flight breakup while maneuvering at the Reno-Stead Airport. The pilot was killed. The airplane was quite small, with a wingspan of 15 feet and length of 16 feet. Its height was four feet, and it had an empty weight of 500 pounds.
An FAA inspector reported that the pilot was participating in an International Formula One Pylon Air Race Class pilot-qualification flight. The flight was intended to be composed of a series of maneuvers that included 360-degree rolls to the left and right, followed by 180-degree rolls to the left and right. These maneuvers were being observed by personnel located on the airport ramp for the purposes of the pilot obtaining a Formula One Racing Pilot License.
The airplane was observed on an east-to-west heading parallel to runway 8 about 1,500 to 1,800 feet AGL. The pilot performed a 360-degree left roll at more than 200 miles per hour. Witnesses reported the airplane seemed to "bobble" and "pitch downwards" prior to abruptly leveling off. They estimated the roll rate was about 400 degrees per second.
The airplane made a climbing 360-degree turn to the left in order to set up for a second pass parallel to runway 8. The airplane exited the 360-degree turn, leveled off, pitched downward in order to gain airspeed, leveled off and proceeded to enter a roll to the right. Two witnesses estimated the airspeed from 220 mph to 240 mph. As the airplane rolled through about 90 to 120 degrees, witnesses stated the right wing separated from the airframe followed by the left wing separating. The airplane crashed at the airport.
Investigation revealed that the airplane was a rebuild of an airplane that had crashed in 2005. The accident airplane was rebuilt using a new Cassutt fuselage and empennage, using Cassutt design plans. However, the manufacturer of the original kit told the NTSB that the trim system on the accident airplane wasn't their design. The accident airplane had a trim system that was adjustable in flight. The original trim system could only be adjusted on the ground.
The accident airplane had a tube-and-fabric fuselage. The fuselage was a tubular steel truss structure that tapered in the cross-section toward the aft end of the airplane. The one-piece wing was of a twin-spar configuration, and manufactured with wood spars, ribs and skins. During a telephone interview, a representative of the company that produces the Cassutt kit told investigators that there's no published maneuvering speed or never-exceed speed for the Cassutt. The representative estimated that if they were to place a maneuvering speed on the airplane, it would be around 200 miles per hour.
The NTSB determined that the probable cause of this accident was the movement of the airplane's modified horizontal-stabilizer trim system during an intentional high-speed aerobatic maneuver that resulted in exceeding the design stress limits of the airplane and an in-flight structural failure. Contributing to the accident was the builder's deviation from the airplane designer's original trim system.
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