Airworthiness Directive · Amendment 39-17139 · Equipment/furnishings
The Boeing Company Airplanes
This AD applies to The Boeing Company Model 747-400 and 747-400D series airplanes; certificated in any category; as identified in Boeing Alert Service Bulletin 747-25A3555, Revision 1, dated July 27, 2011.
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.
Except as required by paragraph (h) of this AD, do the actions specified in either paragraph (g)(1) or (g)(2) of this AD.
(1) Within 24 months after the effective date of this AD, install aluminum reinforcing brackets on the MEC drip shield gutter, in accordance with Work Package 1 of the Accomplishment Instructions of Boeing Alert Service Bulletin 747-25A3555, Revision 1, dated July 27, 2011; and add a reinforcing fiberglass overcoat to the top surface of the MEC drip shield, including doing a general visual inspection for cracking and holes in the top surface of the MEC drip shield, and doing all applicable corrective actions, in accordance with Work Package 3 of the Accomplishment Instructions of Boeing Alert Service Bulletin 747-25A3555, Revision 1, dated July 27, 2011. Do all applicable corrective actions before further flight after doing the general visual inspection.
(2) Do the actions specified in paragraphs (g)(2)(i) and (g)(2)(ii) of this AD.
(i) Within 24 months after the effective date of this AD, install aluminum reinforcing brackets on the MEC drip shield gutter, in accordance with Work Package 1 of the Accomplishment Instructions of Boeing Alert Service Bulletin 747-25A3555, Revision 1, dated July 27, 2011; and install a MEC drip shield drain system, in accordance with Work Package 2 of the Accomplishment Instructions of Boeing Alert Service Bulletin 747-25A3555, Revision 1, dated July 27, 2011.
(ii) Within 96 months after the effective date of this AD, add a reinforcing fiberglass overcoat to the top surface of the MEC drip shield, including doing a general visual inspection for cracking and holes in the top surface of the MEC drip shield, and doing all applicable corrective actions, in accordance with Work Package 3 of the Accomplishment Instructions of Boeing Alert Service Bulletin 747-25A3555, Revision 1, dated July 27, 2011. Do all applicable corrective actions before further flight after doing the general visual inspection.
(1) Boeing Alert Service Bulletin 747-25A3555, Revision 1, dated July 27, 2011, states that Figures 7 and 8 apply to airplanes in Groups 1 and 3; however, Figures 7 and 8 apply to Group 2 airplanes.
(2) Boeing Alert Service Bulletin 747-25A3555, Revision 1, dated July 27, 2011, states that Figures 9 and 10 apply to airplanes in Group 2; however, Figures 9 and 10 apply to Groups 1 and 3 airplanes.
(3) Where Paragraph 1., “Kits/Parts,” of Paragraph 2.C., “Parts Necessary for Each Airplane,” of Boeing Alert Service Bulletin 747-25A3555, Revision 1, dated July 27, 2011, states that Groups 1 and 3 airplanes require top kits 015U1854-1 and 015U1854- 2, Groups 1 and 3 airplanes require top kits 015U1854-3 and 015U1854-4.
(4) Where Paragraph 1., “Kits/Parts,” of Paragraph 2.C., “Parts Necessary for Each Airplane,” of Boeing Alert Service Bulletin 747-25A3555, Revision 1, dated July 27, 2011, states that Group 2 airplanes require top kits 015U1854-3 and 015U1854-4, Group 2 airplanes require top kits 015U1854-1 and 015U1854-2.
