With the forward entry door open, 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.
(1)
Position interior standby control to EXTEND o r exterior control handle to EXTEND and hold selector switch in STANDBY position.
(a)
Positioning of the controls to extend the airstair provides power to energize the door open relay of the airstair door motor. The motor rotates the actuator jackscrew to open the door and cause it to travel inboard and down on the carriage tracks. The initial movement of the door actuates the door-closed switch, which illuminates the STAIRS OPERATING light on the interior control panel. When the door reaches the full open position, the door open switch closes and allows power to energize the airstair extend relay.
(b)
With the airstair extend relay energized, power is supplied to the stair motor which operates the airstair actuator. The actuator drives the carriage pinions that cause the carriage to travel outboard on the rail assemblies. Ball screws attached to the carriage beams drive the ball bearing nuts attached to the upper ladder to extend the upper ladder out of the carriage.
(c)
As the upper ladder begins to rotate down, the mechanism within the ladder side beams causes the lower ladder to unfold from under the upper ladder and raises the handrails.
(d)
When the lower end of the lower ladder contacts the ground, the ladder moves outboard until the carriage actuates the extend switch.
(e)
When the extend switch is actuated, the stair tread lights are illuminated and the STAIRS OPERATING light on the interior control panel goes out.
(2)
When extend cycle is complete, move interior control to OFF or release exterior selector switch and return 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 extensions.
(5)
Extend handrail extensions inside door and latch end of handrail extensions to the support brackets.
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.
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52-61-0 Page 12 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. May 15/69
500 Forward Airstair Retract Sequence
May 01/76 Figure 6 52-61-0
Page 13
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
D. Forward Airstair Retraction - Normal Operation (Fig. 6)
NOTE: The airstair cannot be retracted until the handrail extensions are manually retracted and stowed in the proper position on the handrails.
(1)
Disengage handrail from support brackets just inside forward entry doorway by depressing the latch release button on the underside of the support bracket.
(a) The support brackets are spring-loaded and fold flat against the passenger cabin interior panels when not in use.
(2)
Retract handrail extensions and stow on handrails.
(a)
The forward handrail extension is retracted and stowed by depressing the handrail extension inner tube latch and telescoping the inner tube until the inner tube stop springs into notch to stop inner tube from telescoping. Slide the handrail extension outboard and insert the handrail latch pin in handrail until latched. (See detail B, figure 1.)
(b)
The aft handrail extension is retracted and stowed by sliding the extension outboard and inserting handrail latch pin in handrail until latched.
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