Summary
We are revising an earlier proposed airworthiness directive (AD) that proposed to supersede AD 95-26-11, for all Lockheed Martin Corporation/Lockheed Martin Aeronautics Company Model L-1011 series airplanes. AD 95-26-11 currently requires repetitive inspections to detect cracking of the fittings that attach the aft pressure bulkhead to the fuselage stringers, repetitive inspections to detect cracking of the fittings and of the splice tab of the aft pressure bulkhead, and corrective actions if necessary. The NPRM proposed to reduce the compliance time; add inspections for cracking of certain aft fuselage skin panels; add a structural modification; and also add a post- modification inspection program. The NPRM was prompted by a determination that the fittings at stringer attachments to the upper region of the aft pressure bulkhead are subject to widespread fatigue damage (WFD), which could result in cracking in the aft pressure bulkhead. This action revises the NPRM by reducingthe post-structural modification repetitive inspection interval. We are proposing this supplemental NPRM (SNPRM) to prevent simultaneous failure of multiple stringer end fittings through fatigue cracking at the aft pressure bulkhead, which could lead to rapid decompression of the airplane. Since this action imposes an additional burden over that proposed in the NPRM, we are reopening the comment period to allow the public the chance to comment on these proposed changes.