Audio Control Panel
When a transmission button is pressed, it selects the associated radio for transmission and at the same time, deselects the previously selected radio. Selection is indicated by illumination of three green lights. The transmission keys all have CALL lights that illuminate with SELCAL on the VHF and HF radios.
VHF/HF - When pressed, allows communication on applicable transceiver. CALL flashes when a SELCAL is received on the applicable radio.
PA - Used for PA transmission via boom, oxygen mask, or hand mike. The transmission button must be pressed and held to use the PA system.
CAB - When pressed, allows communication on the cabin interphone system. ATT flashes when a call is received from a flight attendant station. Light extinguishes after 60 seconds if not reset.