737 Flight Crew Operations Manual
Communications -
System Description
Boeing Proprietary. Copyright © Boeing. May be subject to export restrictions under EAR. See title page for details.
5.20.2 D6-27370-866-EGP
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.
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.
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.
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.
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.
The ACP transmitter selectors are not functional. Any transmission from that
station must be from the radio shown on the chart below. The transmitter selector
for the usable radio illuminates when a station is operating in the degraded mode.
The receiver switches are not functional, and only the usable radio is heard at a
preset volume, through the headset. The speaker and speaker switch are not
functional at that station. In addition, the flight interphone and service interphone
cannot be used. The control wheel PTT switch INT position and the ACP PTT
switch I/C position are not functional since the flight interphone is not functional.
September 24, 2015
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