AD FAA-2010-0480

We are adopting a new airworthiness directive (AD) for certain The Boeing Company Model 747-400 and 747-400D series airplanes. This AD was prompted by a report of an in-flight multi-power system loss of the <greek-i>1, <greek-i>2, and <greek-i>3 alternating current electrical power systems located in the main equipment center (MEC). This AD requires installing aluminum gutter reinforcing brackets to the forward and aft drip shield gutters of the 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. This AD also provides 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. We are issuing this AD to prevent water penetration into the MEC, which could result in the loss of flight critical systems.