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 cracks in horizontal stabilizer lower skins. This proposed AD would require repetitive inspections for cracking of the horizontal stabilizer lower skin, and corrective actions if necessary. This proposed AD also provides actions that would terminate certain repetitive inspections. We are proposing this AD to detect and correct cracks in horizontal stabilizer lower skins resulting in reduced local stiffness of the horizontal stabilizer, which can cause heavy vibration leading to loss of structural integrity of the horizontal stabilizer.