Summary
We propose to adopt a new airworthiness directive (AD) for certain Model 737-200, -300, -400, and -500 series airplanes. This proposed AD would require repetitive inspections for cracking of certain fuselage frames and stub beams, and corrective actions if necessary. This proposed AD also provides for an optional repair, which would terminate the repetitive inspections. For airplanes on which a certain repair is done, this proposed AD would also require repetitive inspections for cracking of certain fuselage frames and stub beams, and corrective actions if necessary. This proposed AD results from reports of the detection of fatigue cracks at certain frame sections, in addition to stub beam cracking, caused by high flight cycle stresses from both pressurization and maneuver loads. We are proposing this AD to detect and correct fatigue cracking of certain fuselage frames and stub beams and possible severed frames, which could result in reduced structural integrity of the frames.This reduced structural integrity can increase loading in the fuselage skin, which will accelerate skin crack growth and could result in rapid decompression of the fuselage.