Audio Control Panel ACP
The Audio Control Panel is used by the crew to communicate with ATC, cabin crew, passengers, listen to radio beacons and to communicate with each other.
In the Boeing 737 cockpit there can be found 3 audio control panels. Two of the audio control panels can be found on the center pedestal, one for the Captain on the left side and the other for the First Officer on the right side. The third is for the observer or safety pilot located in the overhead panel.
The squared transmitter selector switches on top of the panel are used to select the channel were the pilots communicate on. From left to right this is VHF1, VHF2, VHF3, HF, Service Interphone, Flight Interphone and PA (Public Address).
Under de Transmitter selector you will find the receiver switches. These switches can be pushed and rotated. When the switch is illuminated white, the switch is active and allows the reception of the related system or navigation receiver. Pilots can receive multiple communication channels when more switches are pushed.
Push to talk switch
The push to talk switch is spring loaded to neutral. The switch is used to select R/T or I/C to transmit on these channels (R/T as selected by the transmitter selector and I/C for direct transmission over flight interphone). The switch can also be used when the push to talk switch on the control column is not functioning properly.
MASK BOOM switch
The MASK BOOM switch is used to select between the oxygen mask microphone (MASK) or the microphone in the headset (BOOM). In an event that the crew should where their oxygen masks (smoke in the cockpit, rapid decompression), the crew will select this switch to MASK just after they have put their masks on.
The speaker switch is used to let the selected communication through from the selected receiver be heard on the overhead speaker. The knob can be rotated to adjust the volume. When pushed the audio is selected, when pushed again the audio is deselected.
Alternate Normal Switch
This switch selects if the ACP operates in the normal mode or the Alternate (degraded) mode.
When this switch is selected to V (Voice), the ACP will receive only NAV and ADF voice audio. When selected on R (Range), is will received NAV and ADF station identifier range (code)audio. When selected on B (Both), the ACP will receive NAV and ADF voice and range audio.