Summary
We propose to adopt a new airworthiness directive (AD) for certain The Boeing Company Model 737-900 and -900ER series airplanes. This proposed AD was prompted by reports of early fatigue cracks at chem-mill areas on the crown skin panels. This proposed AD would require repetitive inspections for cracking of the fuselage skin along chem-mill steps at certain crown skin and shear wrinkle areas, and repair if necessary. We are proposing this AD to detect and correct fatigue cracking of the skin panel at the specified chem-mill step locations, which could result in rapid decompression of the airplane.