NTSB Identification: SEA07LA217.
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Accident occurred Saturday, July 28, 2007 in West Linn, OR
Probable Cause Approval Date: 03/31/2008
Aircraft: Taylorcraft BF12, registration: N13060
Injuries: 2 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 67-year-old float equipped Taylorcraft crashed into a river following a wing lift strut separation. A witness reported that it appeared the airplane was going to land; however, just before touchdown it began to ascend and enter a left turn. The witness said that shortly after entering the turn, the airplane's left wing buckled and folded back against the fuselage. The airplane then entered an uncontrolled descent to impact with the water. Visual examination of the fractured wing strut attachment fitting showed substantial corrosion and pitting throughout the assembly. Further examination utilizing a scanning electron microscope (SEM) revealed that the left wing strut fitting fractured due to extensive corrosion followed by fatigue cracking. The lower side of the fitting had corrosion pitting that extended from the interior of the fitting completely through the thickness in some areas. The upper side of the fitting was also thinned due to corrosion. Several areas of the fracture surfaces showed oxidation consistent with progressive crack growth over an extended period of time, and fatigue features were found in areas not damaged by rubbing or corrosion. The most recent annual inspection was completed 2 months prior to the accident by the owner, who held an airframe and powerplant technician license. It was not determined which one of the two pilots, an airline transport pilot/certified flight instructor (also the owner of the airplane) seated in the left front seat or the airline transport pilot/certified flight instructor (CFI) seated in the right front seat, was manipulating the flight controls when the accident occurred.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The corrosion, fatigue fracture, and subsequent separation of the left wing lift strut attachment fitting. Also causal was the inadequate maintenance and annual inspection by the owner/pilot/mechanic. Full narrative available
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