CARGO COMPARTMENT DOORS - DESCRIPTION AND OPERATION
1. General
A. There are two cargo compartment doors on the lower right side of the fuselage, one serving each cargo compartment. (See figure 1.) Both are plug-type, inward opening doors, hinged at their upper edges and operated manually from either inside or outside the airplane. Except for slight differences in shape, both doors are similar in design and operation.
B. The forward cargo compartment door provides access to the oxygen storage cylinders which are located in the forward cargo compartment.
C. Each cargo door is an alclad structure with outer and inner skin and internal webs and stiffeners. The door is hinged from the fuselage structure by two hinge arms on its upper edge which are adjustable through the use of serrated plates and shims. The forward and aft cargo doors are equipped with a centering device. Two rollers at the fore and aft door edges locate the door in the closed position by engaging roller stop fittings on the door jambs. Around the periphery of the door a continuous sealing strip prevents loss of cabin pressure around the door edges when the airplane is in flight. Pressurization loads on the door are transmitted to the fuselage by twelve adjustable stop fittings attached along the forward, aft, and lower edge of the door, which bear against corresponding stop pads attached to the fuselage structure surrounding the door. Loads on the upper edge of the door are transmitted to fuselage structure by the two hinge arms. Two access panels in the outer skin provide external access to the door latching mechanism to open the door in the event of failure of the latching mechanism.
D. Each door is equipped with a balance mechanism which counterbalances the weight of the door and thus, facilitates door opening. A snubber, installed between the hinge arms on each door, restrains the free fall of door from the open position if the balance mechanism cable fails. A positive mechanical latch on each door secures it in the fully open position while this condition is desired. Each door has a door warning switch.
2. Latching Mechanism
A. The door latching mechanism consists of an internal horizontal torque tube at each end of which a short arm carrying a latching roller protrudes beyond the edge of the door. These latching rollers engage latch fittings attached to the fuselage structure. The torque tube in the door is connected to the operating handle assembly, which consists of a short shaft passing through the thickness of the door, with an operating handle at each end. The handle on the inboard side of the door projects beyond the inboard skin, but the outboard handle is spring-loaded so that it retracts flush with the exterior surface when it is released after use. A recessed finger access pan adjacent to the handle provides access for the fingers when the handle is to be used.
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Nov 15/69 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 52-31-0 Page 1
Cargo Compartment Doors Component Location 526
52-31-0 Figure 1 Apr 01/97
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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
3. Balance Mechanism
A. Door balance is maintained by helical extension springs attached to the upper aft inner edge of the door, between the inner web and outer skin. The springs connect to a cable assembly that is wound on a cable drum mounted on the forward inner structure of the door. (See figure 1.) From the cable drum the cable runs over two pulleys mounted on the inner structure of the door, through a grommet in the door inner web, and connects to an overhead floor beam. The cable grooves in the cable drum have a decreasing radius in order to provide a constant tension in the cable system as the door is opened and closed. The balance mechanism is arranged so that when the door is closed the springs are stretched; when the door is opened the springs contract to raise the door to or near the open latched position.
4. Operation
A. The door is opened from outside the airplane by pulling the door handle out of its recess and rotating it counterclockwise. Rotation of the handle actuates a torque tube to withdraw the latch rollers from their latch fittings. As the door swings inboard, under tension of the door balance mechanism, the door warning proximity switch is actuated to energize the appropriate door warning light in the control cabin. As soon as the door has moved clear of its latch fittings, the handle may be released. Springs within the handle will cause it to return to its normally locked and recessed position. With little or no manual effort, the door may be swung open until the spring-loaded mechanical latch on its lower edge engages with a fitting under the fuselage floor structure. The door may also be opened from inside the airplane, using the nonretracting inner handle. In this case the procedure is similar except that rotation of the handle appears clockwise to the operator. Access to the inside handle is obtained by pulling aside the cargo net which extends from the ceiling to the lower edge of the door.
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