NTSB Identification: LAX02FA134.
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Accident occurred Thursday, April 11, 2002 in Willows, CA
Probable Cause Approval Date: 06/30/2004
Aircraft: Beech G35, registration: N4487D
Injuries: 2 Fatal.
NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.
According to witnesses, the airplane was seen approaching the motor sports park from the southwest at approximately 1,200 feet agl and at a "faster than usual" rate of speed. The airplane was in a "sharp, 90-degree bank," as it began to circle the park in a level turn. After circling around to the east, the airplane returned to a wings-level attitude and began to climb. Shortly thereafter, the tail of the airplane began to "shake violently" and separate from the airplane. One witness said he heard a loud noise as "the tail came off, and all of it started falling apart." He said the tail section separated first, then the airplane pitched over, and the left wing broke off. Witnesses saw the airplane enter a downward spiral. As the airplane descended, the engine separated and the passenger was ejected. The airplane then entered an inverted flat spin and impacted the ground 1,000 feet north of park. An examination of the airplane's left wing, and stabilizers revealed structural failures consistent with overload. According to the manufacturer's Flight Strength Diagram or Vn diagram for the G35, abrupt control column deflection at a speed of 113 knots (Va, or maneuvering speed) could produce a 4.4 G structural load (Limit Load factor), while abrupt control column deflection at or above 152 knots (Vno/Vc, or maximum structural cruise speed) could produce a 6.6 G structural load (Ultimate Load limit). Examination of the recorded radar data disclosed that the airplane was traveling at 142 knots at the time of the breakup. Engineering analysis concluded that in a level turn, the bank angle required to achieve Limit Load is 76.8 degrees, and the bank angle required to achieve the Ultimate Load is 81.2 degrees. FAA toxicology testing of the pilot revealed the presence of Diphenhydramine in urine, and Norverapamil, and Verapamil in urine and liver.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: the pilot's entry into an abrupt maneuver at an excessive airspeed beyond Va, which resulted in exceeding the aircraft's design stress limits. Full narrative available
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