Fatigue fracture folds wing in flight

This June 2007 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.

Aircraft: Taylorcraft BF12.
Location: West Linn, Ore.
Injuries: 2 Fatal.
Aircraft damage: Destroyed.

What reportedly happened: According to witnesses, it appeared that the 67-year-old float-equipped Taylorcraft was going to land on the river. However, just before touchdown it began to climb to the left. The left wing buckled and folded back against the fuselage. The airplane then entered an uncontrolled descent into the water.

Examination of the fractured wing strut attachment fitting showed substantial corrosion and pitting throughout the assembly. Further examination utilizing a scanning electron microscope 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 two months prior to the accident by the aircraft owner, who held an airframe and powerplant technician license.

Probable cause: The corrosion, fatigue fracture, and subsequent separation of the left wing lift strut attachment fitting. The inadequate maintenance and annual inspection by the owner/pilot/mechanic was a factor.

For more information: NTSB.gov/ntsb/brief.asp?ev_id=20070808X01147&key=1.

Comments

  1. A comment on how to inspect older aircraft, or a source of inspection techniques would have been helpful in this case. Many of us have older aircraft and constantly are concerned with age and fatigue problems and can use all the help and suggestions we can get.

    Thanks

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