Plane & Pilot
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.
After a highly modified World War II P-51 Mustang crashed into spectators at the National Championship Air Races at Reno-Stead Airport, Reno, Nev., this past September, there was the predictable criticism of air races being an excessively dangerous sport for participants and spectators alike. The death toll quickly rose to 11, including the pilot with about 70 injured. Enthusiasts and air race organizers defended the activity, noting that only the best-qualified pilots are allowed to participate, and safety is emphasized in everything. The FAA is active in providing oversight and promoting safety for racing events, ranging from prescribing minimum distances between the crowds and aerial activity, to certifying racing check pilots. A records search shows that the NTSB investigated three fatal air racing accidents in the 10 years before the September accident, with about a dozen more if you go back into the '60s. Generally, these previous accidents had in common that the pilots were the fatalities. In the context of extreme speeds and maneuvers, and the informed assumption of risk by the participants, three or four fatal racing accidents in 10 years doesn't seem as grim as a decade's worth of fatal highway accidents, or 10 years' worth of GA fatal accidents involving weather and fuel mismanagement.

Venture M20
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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