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When pushed in, selected the associated channel for transmission and the three green lines illuminate. The channel is deselected by pushing the switch again or selecting another channel. VHF/HF - When pushed, allows communication on applicable transceiver. "CALL" flashes when a SELCAL is received on the applicable radio.
INT - When pushed, allows communication on the flight interphone system. "MECH" flashes when a call is received from the external service interphone panel. Light goes off after 60 seconds if not reset.
CAB - When pushed, allows communication on the Cabin interphone system or service interphone. "ATT" flashes when a call is received from a Flight Attendant station. Light goes off after 60 seconds if not reset.
PA - Used for PA transmission via boom, oxygen mask or hand mike. The transmission switch must be pressed and held to use the PA system. PA announcements can also be made using the cockpit handset without selecting the PA transmission switch. Reception Knobs
Select reception channels and adjust associated audio levels. When knob is released out, the respective channel is selected and the knob illuminates.
INT / RAD Switch
Operates as a press-to-talk switch for boon or oxygen mask microphones. INT - The interphone is "hot" between cockpit crew members, regardless of the transmission switch selection. The INT knob must be selected for reception.
Neutral - Disconnects microphones from transmission. Reception is normal.
RAD - Connects boom or mask microphones to facility selected on the ACP. Spring-loaded to the neutral position. ON Voice Switch
Inhibits ADF and VOR IDENT signals. Switch illuminates when pushed in.
Extinguishes lights in the CALL, MECH and ATT transmission switches.