NATA Receives AMOC for T-6/SNJ Emergency AD

    Just before EAA AirVenture Oshkosh 2009, the North American Trainer Association (NATA) received final paperwork from the FAA on an alternate method of compliance (AMOC) for an emergency airworthiness directive for North American T-6, SNJ, and Harvard aircraft. AD 2005-12-51 was issued in June 2005 after an AT-6 experienced a catastrophic wing failure in May that year.

    The original procedure outlined in the AD was taken from a service letter developed by an FAA-approved repair station in South Africa after a similar failure in a South African Air Force (SAAF) T-6. The inspection called for the removal of all wing attach angle bolts in a specific order, stripping the paint, inspecting for cracks with a fluorescent dye penetrant, and reinstalling the bolts. Inspection interval was mandated at every 200 hours of flight time.

    The entire fleet of approximately 800 U.S. and many foreign aircraft were inspected and no structural cracks were found in the fleet. However, the inspection did uncover other issues with the wing attach angles, which prompted some aircraft to have the wing attach angles replaced.

    EAA Warbirds of America and NATA worked together to find qualified personnel to complete a damage tolerance analysis and crack growth analysis on the lower wing attach angle. Fortunately, a contact made at the National Warbird Operators Conference and the National Research Council of Canada (NRC) was able to complete the study that involved NRC putting strain gauges on a Harvard to flight test and evaluate the data. The results of this study showed that only the forward 7 to 13 inches of the lower wing attach angles needed to be inspected every 200 hours of service. The remainder of the wing attach angles could therefore use an inspection interval of 1,000 hours.

    Armed with this study and guidance of EAA Warbirds of America, NATA asked for an AMOC reflecting the change to the inspection interval. The AMOC also includes approval to use eddy current testing in lieu of the fluorescent dye penetrant inspections. NATA was granted to extend the inspection interval on the upper wing attach angles to an interval of every 1,000 hours rather than the 200 hours based on the findings of the first round of inspections.

    The AMOC is available to any T-6/SNJ/Harvard aircraft owner through NATA, and the AMOC will be recorded by the aircraft’s serial number and owner. For more information, contact NATA at 360-256-0066, or email: natrainer@aol.com.

 

   

     
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