Summary
This document revises an earlier proposed airworthiness directive (AD), applicable to certain Boeing Model 747SP, 747SR, 747-100, 747-200, and 747-300 series airplanes, that would have superseded an existing AD that currently requires repetitive operational tests of the reversible gearbox pneumatic drive unit (PDU) or the reversing air motor PDU to ensure that the unit can restrain the thrust reverser sleeve, and correction of any discrepancy found. The proposed AD also would have required installation of a terminating modification, and repetitive functional tests of that installation to detect discrepancies, and repair if necessary. This new action revises the proposed rule by removing airplanes from the applicability and adding new requirements. The actions specified by this new proposed AD are intended to ensure the integrity of the fail-safe features of the thrust reverser system by preventing possible failure modes in the thrust reverser control system that can result ininadvertent deployment of a thrust reverser during flight. This action is intended to address the identified unsafe condition.