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 747-400 and 747-400D series airplanes. That NPRM proposed installing aluminum gutter reinforcing brackets to the forward and aft drip shield gutters of the main equipment center (MEC); and adding a reinforcing fiberglass overcoat to the top surface of the MEC drip shield, including an inspection for cracking and holes in the MEC drip shield, and corrective actions if necessary. That NPRM also provided for an option to install an MEC drip shield drain system, which, if accomplished, would extend the compliance time for adding the reinforcing fiberglass overcoat to the top surface of the MEC drip shield. That NPRM was prompted by a report of a multi-power system loss in flight of <greek-i>1, <greek-i>2, and <greek-i>3 alternating current electrical power systems located in the MEC. This action revises that NPRM by revising the locating dimensions of the brackets and changing the routing of the forward drain tubes. We are proposing this supplemental NPRM to prevent water penetration into the MEC, which could result in the loss of flight critical systems. 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.