Tuesday, December 20, 2011
Air Race Accidents
Safety in air racing depends on the airplane as well as the pilot
|RENO AIR RACES. A P-51 Mustang accident at the 2011 races in September killed spectators and left the future of the event in question.|
On September 13, 2002, an amateur-built Venture M20 airplane crashed after failure of the left and right horizontal stabilizers and elevators. The accident was at the Reno-Stead Airport, during the sport-class race as part of the annual Reno Air Races. The airplane dove into the ground and was destroyed. The pilot was killed.
FAA inspectors from the Reno Flight Standards District Office were at the airport monitoring air race activities. They responded to the accident site. Witnesses told them that as the airplane was rounding pylon Number 1, the horizontal stabilizers and elevators began flexing and then bent down. The FAA inspectors reported that the wreckage field was 450 feet long. The airplane was extensively fragmented. The airspeed indicator was found in the debris. The needle was trapped between the fractured glass and the instrument face at the 300 knots/red line. Official timers for the Reno Air Races reported to FAA inspectors that based on time over the measured course distance, the airplane was doing 330 knots just before the accident. The airplane was designed with a gross weight design-maneuvering speed (Va) of 156 knots indicated airspeed (KIAS). Never exceed speed (Vne) was 300 KIAS, and the maximum structural cruising speed (Vno) was 265 KIAS. At maximum gross weight, 2,000 pounds, the structure was stressed for positive and negative load factors of +5 and -2.5 G's.
Investigators learned during the developmental flight-test work with a prototype airplane that a spring was needed in the elevator control circuit to add feedback resistance to control forces felt by the pilot in order to prevent pilot-induced oscillation. However, the spring recovered from the wreckage wasn't the specified size. The spring tension was measured and found to be 30% of the required value.
The NTSB determined that the probable cause of this accident was the overload failure of the horizontal stabilizers and elevators due to a pilot-induced oscillation at a speed at or above Vne, which exceeded the design stress limits of the structure. A factor was the use of an improper spring in the control system by an unknown person.
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