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