Summary
We propose to adopt a new airworthiness directive (AD) for certain The Boeing Company Model 737-300 and -500 series airplanes. This proposed AD was prompted by a report indicating that fatigue cracks were found in the lower wing skin of an airplane with winglets installed. This proposed AD would require repetitive inspections for cracking of the lower wing skin, and repair if necessary. We are proposing this AD to address the unsafe condition on these products.