Air Conditioning Access Doors Inner Surface Repair  500 
52-48-11  Figure 801  Aug 15/68 
Page 802 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

APU ACCESS DOOR - DESCRIPTION AND OPERATION
1. General
A.  The APU access door is situated on the aft lower surface of the fuselage and extends from approximately station 1088 bulkhead to station 1156 bulkhead. (See figure 1.) This is a cowl door that is arranged to provide easy access to the APU. The door is supported on the door sill and fuselage lower torque box structure by two hinges on the right edge of the door and by three tension latches that are located on the left edge of the door. The hinges are equipped with locking levers and shear pins to facilitate door removal. An adjustable latch fitting and stop assembly, attached to the lower torque box structure, mates with each latch. Two door-open brace rods, one located near the forward edge and one near the aft edge of the door inner surface, are provided to secure the door in open position. A drain mast (detail A) is situated in the left forward side of the door and diagonally opposite the APU cooling air exhaust duct (detail B) and the air exhaust exit in the door. The drain mast is connected by fluid line tubes to drain cups which are attached by brackets to the inner surface of the door. The tail skid fairing aft assembly is attached to the forward lower surface of the APU access door and extends to station 1114. For information on the tail skid fairing, refer to Tail Skid, Chapter 32.
B.  The door gussets, doublers, clips, intercostals, hinge frame and the two- piece bonded type skin are fabricated from clad aluminum alloy sheet. Tees and latch frame channels are aluminum alloy extrusions. The latches, latch fitting and stop assemblies and hinges are constructed of aluminum alloy and as required of corrosion resistant steel. The drain mast is constructed of an epoxy reinforced plastic glass fabric and the drain cups and the fluid line tubes of corrosion resistant steel. The cooling air duct, flange and outlet are also fabricated from corrosion resistant steel. The door is formed to fair with the fuselage contour when it is closed and latched.
2.  Latching Mechanism
A.  The three tension latch assemblies provide a means of quickly unlatching the APU access door, permitting the door to be opened for easy access to the APU. The latches also provide a positive door lock.
B  The latches are of fail-safe design. Safety features include trigger action and actuator safety and the overcenter toggle action of the latch handle. A fail-safe spring design is incorporated in the trigger mechanism so that failure of the spring will not cause the latch to open.
505 
Feb 15/68  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  52-48-21 Page 1 

APU Access Door  500 
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500  APU Access Door 
Feb 15/68  Figure 1 (Sheet 2) BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  52-48-21 Page 3 

The trigger in the latch handle can be operated by moderate pressure to release the latch handle from the closed and locked position. The latch handle has approximately 15 degrees of free travel and affords as much as an eight-to-one mechanical advantage in latch operation.
C.  The exposed surfaces of the handle and trigger are agreeable in color with the adjacent clad aluminum structure.
3.  Drain Mast
A.  A drain mast (detail A) is located on the forward left exterior surface of the door and diagonally opposite the APU cooling air exhaust exit in the door. The mast is situated on the door at an angle to prevent its being damaged in the event the airplane is scuffed. Fluid line tubes lead from the exterior surface of the mast to drain cups which are attached by brackets to the inner surface of the door. Fluid that enters the cups flows overboard through the tubes and the drain mast.
4.  APU Cooling Air Exhaust Duct
A.  The APU cooling air exhaust duct (detail B) is attached to the aft right interior surface of the door. The duct directs the cooling air from the APU through the cooling air exhaust exit in the door.
5.  Operation
A.  The APU access door is opened by pushing the trigger in each latch handle, using moderate thumb pressure, which releases the latch safety catch allowing the latch handle and hook to begin the movement required to unlatch the door. While manually restraining the door from opening, each latch handle is moved to its full open position. This action disengages the latch hook and the mated latch fitting and allows the door to open. The door is then manually swung open. The free end of each door brace rod is then unlatched from its stowed position on the door inner surface and is used to secure the door in open position.
　
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