NTSB Identification: CHI06LA268.
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Accident occurred Friday, September 22, 2006 in Branson, MO
Probable Cause Approval Date: 11/29/2007
Aircraft: Windler Tri Q2, registration: N6628K
Injuries: 1 Fatal.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The airplane was destroyed when it impacted trees and terrain during an uncontrolled descent, which resulted from an in-flight separation of the right elevator. A witness reported that the airplane appeared to be in a descent as if approaching to land, when something separated from the airframe. A second witness reported the airplane banked to the right, "winged over," and began a clockwise descending spiral. The right elevator was recovered approximately 1,250 feet from the accident site. Examination of the elevator revealed corrosion and fatigue failure of the mid span hinge pivot pin. The examination also noted surface corrosion on the mid span hinge pin in the area of the fatigue failure. Failure of the mid span hinge pin allowed the control surface to buckle, which subsequently fractured the integral torque tube running along the leading edge of the elevator. Flexing of the control surface permitted the outboard end of the torque tube to slide free of the outboard hinge support. This allowed the elevator to separate from the airframe. In addition, the torque tube cutout at the mid span hinge fitting appeared to be oversized from that shown in the aircraft construction plans. The cutout of the torque tube at the mid span hinge support extended around approximately 120 degrees at the forward side of the tube. According to the plans, the cutout for the hinge was shown to be approximately 80 degrees. The reduced cross section on the torque tube due to the oversized cutout resulted in increased stresses in the area of the cutout.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

Fatigue failure, originating in an area of surface corrosion, of the right elevator mid span hinge pin and the subsequent failure of the elevator torque tube. Additional causes are the separation of the elevator from the airframe due to the hinge pin and torque tube failures, and the pilot's inability to maintain control of the airplane after separation of the control surface.

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