This Special Airworthiness Information Bulletin (SAIB) informs the aviation industry of potential non-conforming Military Specifications (MS), Army Navy Standards (AN) and National Aerospace Standards (NAS) fasteners. The SAIB applies to manufacturers, owners, operators, and maintenance personnel of airplanes, rotorcraft, engines and appliances. This SAIB also asks the aviation industry to report fastener failures and other non-conformities. This bulletin focuses on MS 21042 nuts due to their wide usage in aviation, but is relevant to all other standard fasteners.
At this time, the airworthiness concern is not an unsafe condition and does not warrant an airworthiness directive (AD) action under Title 14 of the Code of Federal Regulations (14 CFR) part 39. However, a significant number of past ADs noted possible unsafe conditions caused by non-conforming fasteners.
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