Summary
We are revising an earlier proposed airworthiness directive (AD) for certain Boeing Model 737-600, -700, -700C, -800 and -900 series airplanes. The original NPRM would have required a one-time general visual inspection of frames between body station (BS) 360 and BS 907 to determine if certain support brackets of the air conditioning (A/C) outlet extrusions are installed; medium- and high-frequency eddy current inspections for cracking of the frames around the attachment holes of the subject brackets; and repair if necessary. The original NPRM would also have required installing new, improved fittings for all support brackets of the A/C outlet extrusions between BS 360 and BS 907. The original NPRM resulted from numerous reports of multiple cracks in the frames around the attachment holes of certain support brackets of the A/C outlet extrusions. This action revises the original NPRM by adding an airplane to the applicability and reducing the compliance time for certain airplanes. We are proposing this supplemental NPRM to prevent frame cracking, which, if not corrected, could lead to a severed frame that, combined with cracking of the skin lap splice above stringer 10, could result in rapid decompression of the airplane.