Summary
The FAA is revising an earlier NPRM for an airworthiness directive (AD) that applies to certain Airbus airplane models, as specified above. The original NPRM would have required modifying the thermal insulation system of certain fuselage frames, and modifying the fuselage drainage system. The original NPRM would also have required revising the FAA-approved maintenance inspection program to include inspections for corrosion or cracking in the subject areas. The original NPRM was prompted by reports of corrosion in the lower part of the pressure bulkhead at certain fuselage frames. This action revises the original NPRM by expanding the applicability to include additional airplanes. We are proposing this supplemental NPRM to prevent accumulation of condensation in the insulation blankets of certain fuselage frames, which could cause corrosion that could result in reduced structural integrity of the fuselage and consequent rapid decompression of the airplane.