Action
Supplemental notice of proposed rulemaking (NPRM); reopening of comment period.
Summary
We are revising an earlier proposed airworthiness directive (AD) for certain The Boeing Company Model 747 airplanes. The NPRM proposed to require repetitive inspections for cracking in the bulkhead splice fitting, frame supports, forward and aft inner chords, and floor support; an inspection for cracking in the bulkhead upper web, doubler, and bulkhead lower web; and corrective actions if necessary; for certain airplanes, inspections for cracking in the repaired area of the bulkhead, and corrective actions if necessary; for certain airplanes, support frame modification and support frame inspections, and related investigative and corrective actions, if necessary; for certain airplanes, repetitive support frame post-modification inspections and inspections for cracking in the hinge support, and related investigative and corrective actions if necessary; for certain airplanes, a one-time inspection of the frame web and upper shear deck (floor support) chord aft side for fasteners; and a one-time inspection of the upper forward inner chord, frame support fitting and splice fitting, for the installation of certain fasteners; and related investigative and corrective actions if necessary; for certain airplanes, a one-time inspection of the upper forward inner chord, frame support fitting and splice fitting for the installation of certain fasteners; a one-time inspection for any repair installed on the left and right side of the aft inner chord, and related investigative and corrective actions, if necessary; for certain airplanes, a one-time inspection of the support frame outer chords for cracking, and repair if necessary; and repetitive support frame post- repair inspections, and corrective actions, if necessary. The NPRM was prompted by reports of cracking in the forward and aft inner chord of the body station (BS) 2598 bulkhead near the upper corners of the cutout for the horizontal stabilizer rear spar, and cracking in the bulkhead upper and lower web panels near the inner chord to shear deck connection. This action revises the NPRM by adding an optional terminating action for certain inspections and expanding the inspection area for certain surface and open-hole HFEC inspections. We are proposing this supplemental NPRM (SNPRM) to detect and correct fatigue cracking of the BS 2598 bulkhead structure, which could adversely affect the structural integrity of the bulkhead and the horizontal stabilizer support structure and result in loss of controllability of the airplane. Since these actions impose 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.