526  Forward Airstair Extend Sequence 
Aug 15/72  Figure 5  52-61-0 
Page 9 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

(1)  
Position interior control to EXTEND or exterior control handle to NORMAL EXTEND and hold in that position.

(a)  
Positioning the controls to EXTEND energizes the normal and standby door open relays, thereby energizing the normal and standby door motors. The door open and close relays are interlocked to prevent energizing simultaneously the open and close side of the airstair door motor. The motors drive the actuator jackscrew to move the door inboard and down on the carriage tracks. The door will open rapidly since both door motors are driving the actuator. The initial movement of the door closes the door close switch, illuminating the STAIRS OPERATING light on the interior control panel. When the door reaches its full open position, the door open switch actuates, thereby removing power from the normal and standby door motors. The open switch energizes the normal airstair extend relay. The standby airstair relay is also energized via the speedup switch and speedup relay.

(b)  
With the airstair extend relays energized, power is applied to the normal and standby stair motors to operate the airstair actuator. With both motors energized, the actuator drives the carriage and upper ladder outboard rapidly. Just before the upper ladder rollers enter the curved tracks of the carriage, the speedup switch is released thereby removing power from the standby airstair motor.

(c)  
As the lead rollers of the upper ladder enter the curved tracks of the carriage, the lower ladder lock is triggered to release the lower ladder. Also, the slow-down operating switch is actuated by a ramp on aft carriage beam which energizes the standby airstair motor in the retract mode to slow the rotation of the ladders as they rotate downward. When rotation of the lower ladder is nearly complete the slow down operating-switch is released, thereby de-energizing the standby airstair motor.

(d)  
As the upper and lower ladders reach full extension, the carriage continues to extend until the carriage actuates the extend switches to remove power from the airstair motor.

(e)  
The extend switch, in the actuated position, lights the stair tread lights and turns out the STAIRS OPERATING light on the interior control panel.

(2)  
When extend cycle is complete, move interior control to OFF or exterior control handle to the neutral position.

(3)  
Open forward entry door to the full open position.

(4)  
Disengage handrail extensions from stowed position by sliding handrail latch release outboard and lifting handrail extension (detail C).

(a)  When handrail extensions are disengaged from stowed position on handrails, microswitches in the handrails are actuated to disarm the airstair retract relay. This ensures, for normal system operation only, that the stair cannot be retracted until the handrail extensions are properly stowed on the handrails. For standby operation, the handrail microswitches and relays are bypassed. Actuator retraction using standby mode can be attempted, without stowing the handrails; however, structural damage may result.

(5)  
Extend handrail extensions inside doorway and latch ends of handrail extensions to the handrail support brackets located just inside forward entry doorway.

526 
52-61-0 Page 10  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  Aug 15/69 

526 
May 01/76  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  52-61-0 Page 10A 

(a)  The support brackets are spring-loaded and fold vertically against the passenger compartment interior panels when not in use.
WARNING:  CHECK HANDRAIL LATCHES ARE LOCKED BY STRONGLY SHAKING LATCH FORE AND AFT. SHOULD THE LATCHES NOT BE LOCKED AND COME UNLATCHED, AN INDIVIDUAL COULD FALL SINCE THE HANDRAIL EXTENSIONS DO NOT PROVIDE SUPPORT WHEN UNLATCHED.
C.  Forward Airstair Extension - Standby 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 STANDBY OPERATION SYSTEM WITHIN A 20-MINUTE PERIOD.
AIRSTAIR SHALL NOT BE OPERATED IF WINDS EXCEED 40 KNOTS.
NOTE:  In the event of an electrical failure in the normal system, the standby system is provided to operate the airstair. This system operates from 28-volt dc airplane power or if- airplane power is not available, airplane battery power is used to operate the airstairs.
　
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