The United States Federal Aviation Administration (FAA) has issued an Airworthiness Directive (AD) addressing missing washers on Boeing 737 Next Generation (NG) aircraft, namely the -600, -700, -700C, -800, -900, and -900ER models. According to the FAA, the AD was initiated due to reports of missing washers, incorrect washer type, shanked fasteners, gaps in the fastener head, and incorrect hole sizes found on the left and right sides at a specific station (STA) of the frame inner girder and web. To comply with the directive, airlines must inspect existing repairs and cracks and, if necessary, perform remedial actions. "The FAA is issuing this AD to address cracks in the left and right sides of the STA 727 inner frame and S-18A web before the cracks reach a critical length," the agency said, adding that the cracks could result in a fatigue critical basic structure (FCBS) and the inability of a principal structural member (PSE) to support the ultimate load, which could compromise the structural integrity of the airplane." This is a final AD rule with an effective date of May 30, 2023. The agency estimates that the rule will affect 1.925 U.S.-certified Boeing 737 NGs and calculates that a general visual inspection and a high frequency eddy current (HFEC) and shim installation inspection will cost $170 and $425 per operator, respectively. In the meantime, the “condition-based actions include the installation of a new washer, an HFEC surface inspection of the STA 727 frame inner belt at S-18A for cracks and repair” and