B. Overwing Lights
(1)
There are four overwing emergency exit path lights as shown in Fig. 1. Two overwing light power supply modules are located in the forward part of the aft cargo compartment, one on each sidewall. Each power supply module provides power and control for the two overwing lights on the same side of the airplane. The power supply modules operate the same as the escape slide power supply modules.
(2)
A door-operated switch is located on both overwing escape hatches. When an escape hatch is opened , the switch disables the 28-volt dc power to the adjacent power supply module, causing the lights for that escape hatch to come on if the emergency light switch on the pilots' overhead panel is set to the ARMED position.
7. Operation
A. The emergency exit lights are controlled by a three-position switch, ARMED, ON and OFF, on the forward overhead panel. Each portable emergency exit light also has a two position switch, ARM and ON, integral with the portable assembly (Fig. 2). An additional switch on the aft attendants' panel can override the pilot's emergency light switch to turn all emergency lights on. The attendant's switch has two positions, ON and NORMAL. With the attendant's switch set to NORMAL, the pilot's switch has control of the emergency lights. The hot battery bus supplies power to arm and disarm the emergency lights through individual battery pack control circuits. This enables the emergency lights to be turned on or off with power removed from the airplane. The 28-volt dc bus No. 1 provides power to charge batteries and power failure inputs.
B. During normal airplane operation, the emergency light switch on the pilots' overhead panel is set to ARMED, and the attendant's emergency light switch is set to NORMAL. With the switches set to these positions and the 28-volt dc bus No. 1 energized, all emergency lights will remain off and their batteries will receive a trickle charge. If the 28-volt dc bus No. 1 loses power, the control logic circuit in each emergency light and battery pack will turn its emergency lights on. The lights can be turned off by setting the pilot's emergency light switch to OFF. With the pilot's or attendant's emergency light switch set to ON, the battery emergency lights will come on. With the pilot's emergency light switch set to OFF, the lights will remain off, independent of the 28-volt dc bus No. 1. However, the batteries will receive a trickle charge if the 28-volt dc bus No. 1 is energized.
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33-51-01 Page 8 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. Feb 15/72
C. When the portable emergency exit light assemblies are removed from their mounting plates, the portable lights are controlled by the integral ARM-ON switch, with the ARM being the switch off position. The pilot's emergency light switch should be positioned at OFF before removing any portable light from its mounting plate. If a portable light is removed from its mounting plate with the pilot's switch set to ARMED, the light will come on and remain on. To turn the portable light off under these conditions, set its switch to ON then back to ARM. The light will then go off. This function disables the logic circuitry in the light assembly and control of the light is by its ON/ARM switch until it is reinstalled on a mounting plate.
D. If external power is removed from the aircraft with the emergency lights switch on the pilots' overhead panel in the ARMED position, the lights will come on and discharge all emergency light batteries. The lights should be turned off as soon as possible by placing the emergency light switch on the overhead panel to OFF. If a fixed emergency exit light remains on, it must be replaced.
E. If any portable exit light remains on after the above operation, remove the front cover(s) to gain access to the light switch, and momentarily position the applicable emergency exit light switch to ON then ARM. The light should extinguish. If it remains illuminated, the portable assembly must be replaced.
F. The pilot's emergency light switch should be set to OFF before disconnecting electrical wires or connectors to any emergency light or battery pack. Interrupting power to pin 2 of any light or battery pack with the pilot's switch set to ARMED will cause the disconnected emergency lights to come on and discharge their batteries.
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