(2)
AMM 54-51-03/401, Spring Beam

 (3)
AMM 54-51-03/601, Spring Beam

 (4)
AMM 54-62-00/201, Nacelle Strut Access Panels

 (5)
AMM 54-62-03/501, Trailing Edge Fairing Door

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747-400
MAINTENANCE MANUAL

STRUT SKIN FUSE PIN INDICATION STRIPE
NOTE: TYPICAL INBOARD OR OUTBOARD STRUT. ALTERNATIVE LOCATIONS

Nacelles/Pylons Figure 1
C26859
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
 1.

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747-400 MAINTENANCE MANUAL
 NACELLE STRUT ASSEMBLY - DESCRIPTION AND OPERATION
__________________________________________________
General (Fig. 1)
_______
 A.  The nacelle strut assembly consists of the torque box, fan cowl support beam, strut-to-wing attach hardware, engine attach fittings, firewall, and strut drain system.
Torque Box
__________
 A.  The torque box transmits loads between the engine and wing through attaching hardware.
 B.  The torque box is constructed of spars, bulkheads, ribs, and stiffeners. The inboard and outboard struts differ in length, quantity of ribs, and structure at the stepped-down portion of the closure spar area.
 (1)  
Spars in the torque box include the forward upper spar, closure spar at the upper aft end of the torque box, midspar, and forward and aft lower spars.

 (2)  
Bulkheads in the torque box include the forward and aft engine mount

 bulkheads, and torque bulkhead at the aft end of the torque box.Fan Cowl Support Beam
_____________________
 A.  The fan cowl support beam extends forward of the torque box. The fan cowl panels attach to hinges mounted on the fan cowl support beam.
 B.  The fan cowl support beam is attached to the forward engine mount bulkhead by attach fittings and to the forward upper spar by a support link.
Strut-to-Wing Attach Hardware
_____________________________
 A.  The strut is attached to the wing by the upper link, diagonal brace, side brace or side links, spring beams on the outboard struts, and attach/fuse pins.
 B.  Attach/fuse pins are located at each end of the upper link, diagonal brace, and the aft end of the midspar on inboard struts and the spring beam on outboard struts.
Engine Attach Fittings
______________________
 A.  Engine attach fittings, located below the forward and aft engine mount bulkheads, transmit loads between engine and strut. For description of engine attach fittings, refer to 71-21-00/001.
Firewall
________
 A.  The firewall protects the nacelle strut and systems installed in the strut from high temperatures generated in the engine combustor and turbine sections below the strut.
 B.  The firewall consists of steel or steel clad structural members along the entire lower section of the strut. A fireseal depressor is installed along the forward lower section of the strut to mate with a bulb seal installed on the thrust reversers.
Strut Drain System
__________________
 A.  The strut drain system provides a means for disposal of accumulated fuel or other fluids leaking from system plumbing routed through the strut. Fluids are drained overboard or routed through tubes to the engine drain system.
 B.  Strut drain inlets are provided at the bottom of internal strut compartments. Screens are installed on all strut drain inlets to prevent debris from entering drain tubes.
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