Action
Supplemental notice of proposed rulemaking (NPRM); reopening of comment period.
Summary
We are revising an earlier proposed airworthiness directive (AD) for all Model 747-100B SUD, 747-300, 747-400, and 747-400D series airplanes; and Model 747-200B series airplanes having a stretched upper deck. The original NPRM would have superseded an existing AD that currently requires repetitively inspecting for cracking or discrepancies of the fasteners in the tension ties, shear webs, and frames at body stations 1120 through 1220; and related investigative and corrective actions if necessary. The original NPRM proposed to require modifying the frame-to-tension-tie joints at body stations 1120 through 1220 (including related investigative actions and corrective actions if necessary), which would provide a terminating action for the repetitive inspections. The original NPRM also proposed to require new repetitive inspections after the modification, corrective actions if necessary, and additional modification requirements at a specified time after the first modification. The original NPRM also proposed to remove certain airplanes from the applicability. The original NPRM was prompted by reports of cracked and severed tension ties, broken fasteners, and cracks in the frame, shear web, and shear ties adjacent to tension ties for the upper deck. This action revises the original NPRM by adding repetitive open hole high frequency eddy current (HFEC) inspections for cracking in the forward and aft tension tie channels, and repair if necessary. For certain airplanes, this supplemental NPRM also requires a one-time angle inspection to determine if the angle is installed correctly, and re-installation if necessary; and a one-time open hole HFEC inspection at the fastener locations where the tension tie previously attached to the frame prior to certain modifications, and repair if necessary. This supplemental NPRM also, for the Stage 2 inspections, reduces the initial compliance times for those inspections. We are proposing this supplemental NPRM to detect and correct cracking of the tension ties, shear webs, and frames of the upper deck, which could result in rapid decompression and reduced structural integrity of the airplane.