Summary
We are revising an earlier proposed airworthiness directive (AD) for certain Boeing Model 737-100, -200, -200C, -300, -400, and - 500 series airplanes. The original NPRM would have required doing repetitive internal eddy current and detailed inspections to detect cracked stringer tie clips; measuring the fastener spacing and the edge margin if applicable, and doing applicable corrective and related investigative actions. As a temporary alternative to doing the actions described previously, the original NPRM would have required repetitive inspections of the skin and lap joints for cracks and evidence of overload resulting from cracked stringer tie clips, and applicable corrective actions if necessary. The original NPRM resulted from a report of several cracked stringer tie clips. This action revises the original NPRM by including repetitive external eddy current sliding probe inspections of the lap joints for cracks and evidence of overload resulting from cracked stringer tie clips. We are proposing this supplemental NPRM to detect and correct multiple adjacent cracked stringer tie clips and damaged skin and frames, which could lead to the skin and frame structure developing cracks and consequent decompression of the airplane.