Lavatory Door 500
52-52-0 Figure 1 Nov 15/66
Page 2
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
FORWARD AIRSTAIR AND DOOR - DESCRIPTION AND OPERATION
EFFECTIVITY
Standard Passenger Airplanes
1. General
A. The forward airstair is an integral part of the airplane and when extended it is used to load and unload passengers at the forward entry door. When retracted, the airstair is contained in an area under the passenger cabin floor at the forward entry door location. When the airstair is in the retracted position, the airstair door closes the cutout in the fuselage directly below the forward entry door to form a smooth contour with the fuselage exterior skin. The airstair is designed so it can be used when variations in height from 90.0 to 105.0 inches exist between top of forward entry door threshold and ground (Fig. 1).
B. The airstair is operated electromechanically with both normal and standby operating systems. The standby system permits airstair operation in the event of an electrical failure in the normal system.
C. The airstair operation can be controlled from either inside or outside the airplane. Control from inside the airplane is from a control panel located near the upper aft corner of the forward entry door. Control from outside the airplane is from a control handle located near the lower aft corner of the forward airstair door. The STAIRS OPERATING light on the interior control panel illuminates when the airstair door and the stair are in an operating cycle. The light will remain illuminated as long as the stair is in any position other than full extend with the airstair door open, or full retract with the airstair door closed. The STAIRS OPERATING light will operate if dc power is provided by the normal airplane system either in normal or standby mode. If dc power is lost, the battery will provide power for airstair operation, but the STAIRS OPERATING light will not be active.
D. Inadvertent extension of the airstair in flight is prevented by a latch pin which prevents the airstair door from moving inward from the closed position. The latch pin can only be retracted by opening the forward entry door or by operating the airstair exterior control handle.
E. The airstair door is provided with microswitches which energize door warning lights on the control cabin forward overhead panel and master caution lights on the flight crew panel. These lights are illuminated whenever the airstair door is UNLOCKED or OPEN and go out when the door is CLOSED and LOCKED (Ref 52-71-0, Door Warning System).
F. Power for operating the airstair is from main load control center panel (P6). The normal system uses airplane ac and dc power. The standby system uses airplane dc and/or battery dc power. Battery dc power is locked out when airplane dc power is on (Fig. 2 and 3).
May 1/76 52-61-0 Page 1
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
Forward Airstair and Door 500
52-61-0 Page 2 Figure 1 (Sheet 1) BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. Jul 15/70
522 Forward Airstair and Door
May 15/69 Figure 1 (Sheet 1A) BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 52-61-0 Page 2A
563 Forward Airstair and Door
Feb 15/77 Figure 1 (Sheet 2) BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 52-61-0 Page 3
G. The entire airstair assembly and/or various component parts of the airstair assembly can be removed for maintenance or replacement. For maintenance and service, access to the airstair can be gained through the door cutout when the stair is extended, or by removal of panels in the electronics compartment moisture shroud.
2. Operation
A. General
(1)
There are three modes of operation for the forward airstair and door; normal, standby, and manual. For normal operation, the airstair uses 115 volt ac 3 phase 400 cycle power from ac bus No. 2, and the airstair door uses 28 volt dc power from dc bus No. 1. For standby operation, the airstair and the airstair door both use 28 volt dc airplane or battery power from the battery bus. When standby operation is selected, the handrail stowed limit switches are bypassed. During the retract cycle, it is important the handrails are stowed to avoid structural damage. For maintenance or emergency purposes, the airstair may be extended and/or retracted manually, and the airstair door may be operated manually and independent of the airstair. Airstair must be resequenced prior to power operation following manual extension and/or retraction. Manual operation and resequencing of airstair is described in the maintenance practices section, Forward Airstair - Manual Operation.
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