Summary
We propose to adopt a new airworthiness directive (AD) for certain Learjet Inc. Model 60 airplanes. This proposed AD was prompted by an evaluation by the design approval holder (DAH) indicating that the upper fuselage skin under the aft oxygen line fairing is subject to multi-site damage (MSD). This proposed AD would require a one-time inspection of the fuselage skin for corrosion and related investigative and corrective actions if necessary. We are proposing this AD to address the unsafe condition on these products.