CAUTION:  PREMATURE RELEASE OF THE EXTEND SWITCH WILL ALLOW AIRSTAIR TO FREE FALL WITH SPEED CONTROLLED BY THE CENTRIFUGAL GOVERNOR. THIS WILL SHORTEN THE LIFE OF THE GOVERNOR.

(3)  
To prevent inadvertent operation of the emergency system during a normal stair extension, the emergency system is rendered imperative when the airstair has moved approximately 15 degrees in the extend direction. This is achieved by a cam and follower arrangement at the door hinge. This mechanism collapses the overcenter linkage, which locks out the emergency latch mechanism.

(4)  
To retract the airstairs, operate the internal or external switch to the RETRACT position. The stairs will retract to the full UP position. In the full UP position, the retract limit switch in the transmission unit will de-energize the power unit. As this occurs, position the console control handle to the DOOR LATCHED position to secure the aft entry door.

(5)  
Whenever the aft airstairs are extended (power unit de-energized) the treadway lights will illuminate automatically if the aft airstairs tread lights switch is in the AUTO position. However, the lights will be illuminated whenever the switch is in the ON position.

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May 15/68  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  52-14-0 Page 9 

C.  Manual Mode - Interior
(1)  
The manual extension operation of the aft airstair is accomplished by placing the console control handle in the DOOR UNLATCHED position and manually pushing the airstair out the doorway until it free falls.

(2)  
The manual drive attachments are located on the aft end of the aft transmission unit and the forward end of the forward transmission unit (Fig. 2). Access to the aft attachment is thru the lavatory cupboard unit. Access to the forward attachment is thru an opening on the forward side of the windscreen.

(3)  
To retract the aft airstair using the manual drive, place the console control handle in the DOOR UNLATCHED position. Rotate the manual drive counterclockwise. A ratchet wrench and socket on the aft transmission manual drive will serve as a ratchet for the airstair drive system while raising the airstair from the forward transmission manual drive.

WARNING:  DO NOT EXCEED 250 INCH-POUNDS TORQUE ON MANUAL DRIVE.
CAUTION:  PRIOR TO ROTATING THE MANUAL DRIVE, THE CONSOLE CONTROL HANDLE MUST BE PLACED IN THE DOOR UNLATCHED POSITION. THIS PROCEDURE IS NECESSARY TO PREVENT DAMAGE TO THE AIRCRAFT STRUCTURE AND/OR AIRSTAIR MECHANISMS.
NOTE:  Approximately 94 complete turns of the manual drive are required to completely retract the airstairs.
(4)  When the airstairs are fully retracted, place the console control handle in the DOOR LATCHED position.
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D.  Emergency Mode
(1)  Emergency extension of the aft airstairs is accomplished by moving the handle on the control console through its normal range and into the emergency detent position. The first portion of control handle travel in the normal range unlatches and mechanically raises the door to a position where it is clear of surrounding structure. Movement of the control handle into the emergency detent causes a cam in the console to rotate a crank and pull a control rod attached to an arm on a latch release shaft located below the floor. Rotation of this shaft rotates a latch mechanism, which releases the operating arm of a torsion bar installed below the door threshold. The torsion bar arm bears against a roller on the door hinge member. The stored energy in the torsion bar overcomes the effect of stair weight and drive train friction and drives the airstair sufficiently far to initiate a free fall. The airstair will free fall to approximately 70 degrees open and then stop. The center segment is then manually lifted outward to complete the extension. The rate of free fall is limited by a centrifugal governor installed on the aft gearbox pad of the drive mechanism. Whenever an emergency (free fall) extension is accomplished, the electrically controlled three-position switches are rendered temporarily inoperative. This is accomplished internally within the console control panel by mechanical linkage, which opens the door-arming switch. (See figure 3.) Following an emergency extension, the latch system is rearmed by moving the control handle to DOOR UNLATCHED position, then rotating the roller arm on the aft flange of the aft airstair hinge to the SET position engraved on the roller and carrying out a normal retract cycle. Extending the airstair using either the manual or normal mode and returning the roller arm to the NORM position as engraved on the roller completes rearming.
NOTE:  Under adverse conditions of high winds, extreme cold or airplane tilt, it may be required to manually push the airstair out the doorway. After airstair has partially extended, personnel then must lift up and push out the center ladder section. To complete extension when operated from external control, the airstair door may be pulled down.
　
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