Summary
The FAA proposes to adopt a new airworthiness directive (AD) for certain Boeing Model 737-200, -300, -400, and -500 series airplanes. This proposed AD would require a one-time inspection of frames between station 360 and station 907 to determine if a subject support bracket for the air conditioning outlet extrusion is installed, and related repetitive investigative actions and repair if necessary. This proposed AD also provides an optional preventive modification that would end the repetitive investigative actions. This proposed AD would also require a one-time post-modification/repair inspection for cracking of each repaired/modified frame. This proposed AD results from numerous reports indicating that frame cracks have been found at the attachment holes for support brackets for the air conditioning outlet extrusion. We are proposing this AD to detect and correct such cracking, which, if the cracking were to continue to grow, could result in a severed frame. A severed frame,combined with existing multi-site damage at the stringer 10 lap splice, could result in rapid decompression of the airplane.