Airworthiness Directives; The Boeing Company Model 747-400 and 747-400D Series Airplanes

Résumé

We propose to adopt a new airworthiness directive (AD) for certain Model 747-400 and 747-400D series airplanes. This proposed AD would require 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. This proposed 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. This proposed AD results from a report indicating that an operator experienced a multi-power system loss in-flight of 1, 2, and 3 alternating current (AC) electrical power systems located in the MEC. We are proposing this AD to prevent water penetration into the MEC, which could result in the loss of flight critical systems.