525  Forward Airstair Door 
Aug 15/72  Figure 1 (Sheet 2) BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  52-61-500 Page 3 

Forward Airstair Door Lock Mechanism  500 
52-61-500 Page 4  Figure 2 (Sheet 1) BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  Nov 15/68 

500  Forward Airstair Door Lock Mechanism 
Nov 15/68  Figure 2 (Sheet 2) BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  52-61-500 Page 5 

6.  Actuator and Jackscrew
A.  The actuator is an electromechanical device, which converts electrical energy to mechanical rotary motion to turn the door actuator jackscrew. The actuator consists of a gearbox with output shaft, and two identical motor and brake assemblies, primary and standby. Motors are of the series-wound split-field type and have a magnetic brake that engages mechanically when current is removed. The actuator also incorporates a torque-limiting drive clutch to prevent damage due to overload, and a manual drive input when the standby motor is removed from the actuator.
B.  The actuator jackscrew is a ball screw device splined to the actuator gearbox output shaft at one end and connected to the airstair door carriage through the ball nut. A snubber assembly is installed on the jackscrew to protect the actuator from excessive jackscrew travel. The snubber assembly consists of a circular solid rubber snubber bonded at its outer circumference to a metal cover half. An internally splined sleeve insert through the axis of the rubber snubber mates with the jackscrew shaft. The metal cover half has stops for contact with the ball nut stops. If the jackscrew travel exceeds door open switch limits the ball nut stops engage the stops on the snubber, compressing the rubber face and twisting it through 90 degrees with respect to the jackscrew at which point the jackscrew stops are contacted. This braking action reduces the speed at which the stops make contact.
7.  Door Lock and Control
A.  The door lock mechanism consists of actuating levers, control box, telescopic units, cables, rocker arm, and lockpin. When the door is closed and locked, the lockpin engages the door lock bracket on the lower edge of the door. (Fig. 2)
B.  The lockpin can be retracted by two methods while the airplane is on the ground but it cannot be retracted while in flight. Opening the forward entry door or operating the airstair exterior control handle will retract the lockpin.
C.  The rocker arm is connected directly to the lockpin and force applied to either end or to both ends of the rocker arm will retract the lockpin. When the forward entry door is opened, the spring loaded-telescopic unit for the interior control automatically applies a force to one end of the rocker arm. When the exterior control is moved to the open position, a force is applied to the other end of the rocker arm.
525 
52-61-500 Page 6  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  Aug 15/72 

8.  Electrical System
A.  The door electrical system provides for both normal and standby operation. The system consists of a normal dc airstair door motor, a standby dc airstair door motor, relays, and microswitches. (Ref. 52-61-0, Fig.2 and 3)
9.  Operation
A.  By positioning the interior or exterior controls to the EXTEND or RETRACT position, the airstair door can be operated electrically when power is available and the airstair is connected. Either the NORMAL or STANDBY mode of operation may be used. When power is applied to either the NORMAL or STANDBY airstair door motor, the motor drives the actuator, which drives the actuator jackscrew. The actuator jackscrew will then move the door in the carriage and door tracks. (Fig. 1) During EXTEND, power to the airstair motor is automatically removed by either door open switch - NORMAL or STANDBY - when actuated by the door in its full open position. Power is also removed from the airstair door motor automatically during the retract cycle when either door close switch - NORMAL or STANDBY - is actuated by the door in its full close position. The door is locked or unlocked by either the forward entry door or the exterior control handle via the airstair door lock mechanism. Refer to 52-61-0, for system operation.
B.  The airstair door can be operated from the interior or exterior control when the airstair is removed or disconnected by inserting a special plug in the airstair power receptacle. The plug is made from a standard BACC45FT22-19P plug with a jumper of No. 20 wire between pins 9 and 10 for normal system operation. Jumper pins No. 14 and 15 for operation using the standby system. These jumpers functionally replace the airstair NORMAL and STANDBY retract switches in their retract position. Ref. to 52-61-0
　
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