23-43-00
ALL ú ú 01 Page 3 ú Jul 15/94
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
Figure 2
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23-43-00
ALL ú ú 02 Page 4 ú Nov 15/91
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
7. Operation (Fig. 2)
_________
A. Functional Description
(1)
The flight and ground crew call system is turned on by closing the PASS & CREW CALL (or PASS & CREW CALL/LAV SMK DET) circuit breaker, as applicable, on load control center panel, P18. Power to the circuit breaker comes from the 28v dc bus No. 1.
(2)
The CREW CALL HORN circuit breaker on the P6 panel powers the ground crew horn on the nose wheel well area.
(3)
The call system is used to signal the flight crew, attendants, or ground crew to talk on the service interphone system.
(4)
Pressing the PILOT CALL switch on the P19 external power receptacle panel, or the CAPTAIN call switch on either attendant panel, applies 28v dc power to the pilots' CALL light and to the aural warning unit. The CALL light comes on and stays on only while the call switch is pressed. The aural warning unit sounds a single chime.
(5)
Pressing the ATTEND call switch on the forward overhead panel P5, or the ATTENDANT call switch on either of the attendant panels, applies 28v dc power to the attendant call lights, to the attendant call relay, and to the chime in the PA amplifier. The PA amplifier sounds a chime over the PA system. Also, the attendant call relay holds the call lights on until reset with the RESET switch on either attendant panel.
(6)
The RESET switches on the attendant panels are connected in series. Thus, pressing one removes power from the attendant relay and makes the call lights go off.
(7)
Pressing the GRD CALL switch on the forward overhead panel P5 applies 28v dc power to the ground crew call horn. The horn will sound as long as the switch is pressed.
(8)
The ground crew call horn also serves as an audible warning device for the IRS (inertial reference system). The IRS warning system relay comes on in the flight instrument accessory unit or integrated flight instrument accessory unit, and applies 28v dc power to the ground crew call horn, whenever the IRS is powered by its battery or the IRS is turned on and the equipment cooling fan is not operating. The air-ground relay must be in the ground position before the IRS warning system relay can energize. See Ref 34-28-01 for Honeywell IRU or Ref 34-28-02 for Litton IRU.
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