(2)
The chime sound comes from the bell chime module, M1000. It is in the warning electronics unit P51, which is located in the main equipment center. The bell chime module has a chime generator and amplifiers to energize the aural warning loudspeakers.
C. Ground Crew Call Horn_____________________
(1) The attention of personnel outside the airplane is gained by pressing the GND CALL switch. The ground crew call horn in the nose wheel well, will sound when the GND CALL switch is pressed. The crew call horn produces a continuous tone, and operates at 28v dc.
Operation (Fig. 2)
_________
A. Functional Description______________________
(1) The GND CALL circuit breaker on overhead panel P11 controls power to the system. Power from the circuit breaker is routed to the ground crew call relay located in the pilots' call panel and to the FLIGHT DECK CALL SW and GND CALL switches.
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A
757
MAINTENANCE MANUAL
PILOTS' CALL
PANEL
P5 PANEL SEE A P11 PANEL
GROUND CREW CALL HORN
SEE B
NOSE GEAR WHEEL WELL
SELCAL
L-VHF-R L-HF-R
FLIGHT COMPARTMENT B B B B
CABIN CALL
GND FWD MID AFT ALERT CALL
ALERT BBBAB
PILOTS' CALL PANEL
A
P62
CONTROL
PANEL
SEE C
MOM ON
S10035 EMER LT TEST SW
OFF
DOO425 SERVICE INTERPHONE
DOO435
FLIGHT
INTERPHONE
NOSE LANDING GEAR
FLIGHT DECK S00426CALL SW
FIGHT DECK CALL SW
GROUND CREW CALL HORN P62 CONTROL PANEL
B C
Ground Crew Call System Component Location
Figure 1
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757
MAINTENANCE MANUAL
PILOTS CALL PANEL (P5)
Ground Crew Call System Schematic
Figure 2
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MAINTENANCE MANUAL
(2)
Flight compartment calling from the P62 CONTROL PANEL is controlled by the FLIGHT DECK CALL SW button and the ground crew call relay. When the FLIGHT DECK CALL SW button is pressed, a hold-in circuit keeps the ground crew call relay energized for 30 seconds. The ground crew call relay, when energized, lights the pilots' call panel GND CALL light and generates a single chime over the aural warning speakers.
(3)
When the GND CALL switch is pressed, power is applied to the ground crew call horn through the de-energized contact of the IRS warning relay. The ground crew call horn will sound for as long as the GND CALL switch is pressed.
(4)
The IRS warning relay can be energized by a control signal from the equipment cooling system (Ref 21-58-00/001). The ground crew call horn will sound to indicate equipment cooling failures.
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