.
cancels call

.
disconnects the handset from the public address system.

Master Call Lights
Illuminated –
.
amber – a lavatory call switch is activated.

.
pink – flight deck or other flight attendant station is calling.

.
blue – a passenger seat call switch is activated.

Copyright . The Boeing Company. See title page for details.
5.10.32  June 1, 2005

737 Flight Crew Operations Manual

Introduction
The communication system includes:
.  
radio communication system

.  
interphone communication system

.  
cockpit voice recorder system

.  
communication crew alerting system

The communication systems are controlled using the:
.  
audio control panels YA613 - YA687, YC153, YC154, YD651 - YK104

.  
radio tuning panels
YA721 - YA809, YC411, YC413

.  
radio communication panels

Audio Systems and Audio Control Panels
An ACP is installed at the Captain, First Officer, and Observer stations. Each panel controls an independent crew station audio system and allows the crewmember to select the desired radios, navigation aids, interphones, and PA systems for monitoring and transmission.
Transmitter selectors on each ACP select one radio or system for transmission by that crewmember. Any microphone at that crew station may then be keyed to transmit on the selected system.
Receiver switches select the systems to be monitored. Any combination of systems may be selected. Receiver switches also control the volume for the headset and speaker at the related crew stations. Audio from each ACP is monitored using a headset/headphones or the related pilot’s speaker.
Audio warnings for altitude alert, ground proximity warning, collision avoidance, and windshear are also heard through the speakers and headsets at preset volumes. They cannot be controlled or turned off by the crew.
Speakers and Headsets
Each crew station has a headset or headphone jack. The Captain and First Officer have speakers on the ceiling above their seats. There is no speaker at the observer station. Headset volume is controlled by the receiver switches. Speaker volume is controlled by the receiver switches and also the speaker switch.
Copyright . The Boeing Company. See title page for details.
Communications -System Description 737 Flight Crew Operations Manual

Microphones
Hand microphones and boom microphones may be plugged into the related jacks at the flight deck crew stations. Each oxygen mask also has an integral microphone.
YA626, YA721 - YK104 The MASK-BOOM switch allows selection of the oxygen mask microphone or the boom microphone. The MASK–BOOM switch does not affect the operation of the hand microphone.
YA613, YA686, YA687 An oxygen mask microphone is enabled and the boom microphone is disabled when the left oxygen mask panel door is open. The oxygen mask microphone is disabled and the boom microphone is enabled when the left oxygen mask panel door is closed and the RESET/TEST Switch is pushed.
YA626 - YK104 Each hand microphone has a PTT switch to key the selected audio system. The PTT switches on the control wheel or ACP are used to key the oxygen mask or boom microphone, as selected by the R/T and I/C switch. The R/T and I/C switch does not affect the operation of the hand microphone.
YA613 Each hand microphone has a PTT switch to key the selected audio system. The PTT switches on the control wheel or ACP are used to key the oxygen mask or boom microphone, as selected by the RADIO/INT switch. The RADIO/INT switch does not affect the operation of the hand microphone.
YC153, YC154, YD651 - YK104 A MIC switch mounted on the captain’s and first officer’s glareshield panel is used to key the oxygen mask or boom microphone, as selected by the transmitter switch on that pilot’s ACP. Pushing the glareshield MIC switch is the same as pushing the control wheel MIC switch.
Normal Audio System Operation
The Captain, First Officer, and Observer audio systems are located in a common remote electronics unit in the E/E compartment. They function independently and have separate circuit breakers. The audio systems are normally controlled by the related ACPs through digital or computerized control circuits.
Copyright . The Boeing Company. See title page for details.
5.20.2  June 1, 2005

Communications -System Description 737 Flight Crew Operations Manual
Degraded Audio System Operation
If the remote electronics unit or ACP malfunctions, the ACP cannot control the remote electronics unit. Audio system operation can be switched to a degraded mode by placing the ALT–NORM switch to ALT. In this mode, the ACP at that station is inoperative and the crewmember can only communicate on one radio.
　
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