737 MAX Flight Crew Operations Manual
Communications -
System Description
5.20.2
MN-FLT-OH-201
The two flight compartment speakers are muted for the Captain’s and First
Officer’s push-to-talk microphone operation. The speakers are not muted for
oxygen mask microphone operation.
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.
1B785, 1B786
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.
1B401, 1B402, 1B801 - 1J594
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.
1B785, 1B786
The R/T and I/C switch is spring loaded to the neutral position when pressed to
R/T. When pressed in the I/C position it latches.
1B401, 1B402, 1B801 - 1J594
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.
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.
March 1, 2021
