Summary
We propose to adopt a new airworthiness directive (AD) for certain The Boeing Company Model 737-300, -400, and -500 series airplanes. This proposed AD was prompted by reports of fatigue cracking found at the left-side and right-side upper frame, at a certain area. This proposed AD would require repetitive medium frequency eddy current (MFEC) inspections for cracking of the left-side and right-side upper frame, and repair (including open hole high frequency eddy current (HFEC) inspections for cracking of fastener holes) if necessary. This proposed AD also provides an optional preventative modification which would terminate the repetitive inspections at the modified location. We are proposing this AD to detect and correct fatigue cracking, which if not corrected, can grow in size and result in a severed frame, which could lead to rapid decompression and reduced structural integrity of the airplane.