AD FAA-2013-0304

We are adopting a new airworthiness directive (AD) for certain The Boeing Company Model 747-400, -400D, and -400F series airplanes. This AD was prompted by a report of water leakage into the main deck cargo wire integration unit (WIU). The water flowed from the main deck floor panels, through disbonded seams in the aft main equipment center (MEC) drip shield gutter, then onto the WIU. This AD requires cleaning the aft MEC drip shield gutter; and doing a one-time general visual inspection for disbonded seams, and repair if necessary. This AD also requires installing a fiberglass reinforcement overcoat to the underside of the bonded seams of the aft MEC drip shield gutters. We are issuing this AD to prevent water penetration into the MEC, which could result in the loss of flight critical systems.