(2)  
For normal and standby operation, the airstair and airstair door function in response to sequenced control signals (Fig. 2 and 3). The control signals are initiated by actuation of either the interior or exterior controls (Fig. 1). The interior control panel is located near the upper aft corner of the forward entry door. The exterior control handle is located near the lower aft corner of the forward airstair door. The controls for airstair lighting are located on the attendants forward auxiliary panel. For airstair positions during various phases of operation, see Fig. 4.

(3)  
When operating the airstair from the interior control panel, the forward entry door must be unlatched so the airstair door latch pin will retract to unlock the airstair door. Unlatching the entry door also energizes an interlock relay allowing control power to be applied to the interior control panel. The relay is energized when the door warning circuit is actuated and prevents application of power to the airstair door motor while the airstair door is still latched. The interlock relay also prevents operation of the airstair from the internal control when airplane power is not available. The external control must be used to apply battery power. Also the entry door should be open far enough to provide good visibility of the area below the entry door (Fig. 2 and 3).

(4)  
When operating the airstair from the exterior control handle, the forward entry door can be either open or closed because actuation of the control handle will retract the airstair door latch pin. 

(5) 
 The interior and exterior controls are wired in parallel and have equal operating control once the forward entry door is open and the interlock relay energized.

(6)  
During maintenance or when power is not available, the airstair door may be operated manually by removing the standby motor and applying torque to the input drive shaft of the actuator.

(7)  
When the airstair is removed from the airplane, the airstair door can be electrically operated by using a special plug that can be inserted into the airstair power receptacle. The plug is made from a standard BACC45FT22-19P plug with pins No. 9 and 10, for normal system, and pins No. 14 and 15, for standby system, connected by No. 20 wire.

(8)  
The airstair should not be extended when the airplane is jacked or in any attitude that would prevent the lower ladder from firmly contacting the ground. Use of the airstair while unsupported could cause damage.

521 
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526  Forward Airstair Normal System Circuit 
Oct 20/89  Figure 2  52-61-0 
Page 5 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

Forward Airstair Standby System Circuit  526 
52-61-0  Figure 3  Aug 15/69 
Page 6 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

500  Forward Airstair Extension Positions 
May 15/67  Figure 4 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  52-61-0 Page 7 

B.  Forward Airstair Extension - Normal Operation (Fig. 5)
WARNING:  WHEN OPERATING AIRSTAIRS FROM INTERIOR CONTROL PANEL, OPEN ENTRY DOOR TO COCKED POSITION TO ALLOW CLEAR VISIBILITY OF AREA OUTSIDE AIRPLANE TO PREVENT INJURY TO PERSONNEL. DO NOT OPEN DOOR BEYOND COCKED POSITION WHILE OPERATING AIRSTAIR OR EQUIPMENT MAY BE DAMAGED.
CAUTION:  THE AIRSTAIR SHOULD NOT BE OPERATED MORE FREQUENTLY THAN THREE CONSECUTIVE CYCLES WITH NORMAL OPERATION SYSTEM WITHIN A 20 MINUTE PERIOD.
AIRSTAIR SHALL NOT BE OPERATED IF WINDS EXCEED 40 KNOTS.
NOTE:  With the airstair retracted and the airstair door and forward entry door closed and latched, it is mechanically and electrically impossible to extend the airstair until the airstair door latch pin has been retracted. Opening the forward entry door or positioning the exterior control handle to NORMAL EXTEND retracts the airstair door latch pin and allows application of electrical power for airstair extension. Whenever the latch pin is retracted, the door open warning lights on the control cabin forward overhead panel and the master caution lights on the flight crew's panel will be illuminated. 
With the forward entry door unlatched, either the interior or exterior controls may be used to extend the airstair. Whichever control is used, the control must be held in the position required to extend the airstair until the entire extend cycle is complete.
507 
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