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

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We are adopting a new airworthiness directive (AD) for the products listed above. This AD requires a general visual inspection for cracks and holes of the main equipment center (MEC) drip shields, and repairs if necessary; installation of a fiberglass reinforcing overcoat; and, for certain airplanes, installation of stiffening panels to the MEC drip shields. This AD was prompted by a report of a loss of bus control unit number 1 and generator control units numbers 1 and 2 while the airplane was on the ground, and multiple operator reports of cracked MEC drip shields. We are issuing this AD to prevent water penetration into the MEC, which could result in the loss of flight critical systems.