190-00734-11 GTX 33X and GTX 3X5 ADS-B Maintenance ManualRev. 6 Page 3-23.1 GTX 330/330DFigure 3-1 GTX 330/330D Front PanelFunction Selection KeysThe function selection keys are:OFF Powers off the GTX 330.STBY Selects the standby mode. Pressing the STBY key when the GTX 330 is powered offautomatically powers the unit on in standby mode. When in standby mode, the transponderdoes not reply to interrogations. If using software v8.02 or later, GND mode isautomatically determined using either a squat switch or calculated data from various systeminputs including GPS data from an approved control/display unit such as a GTN 6XX/7XX,GNS 400W/500W Series, or GNS 480.ON Selects Mode A and Mode S. Pressing the ON key when the GTX 330 is powered offautomatically powers on the unit in Mode A and will transmit a squawk code wheninterrogated.The transponder replies to Mode A and Mode S interrogations, as indicated bythe reply symbol (®). The replies do not include altitude information.NOTEIf the transponder is in the ON or ALT operating mode, the transponder becomes an activepart of the Air Traffic Control Radar Beacon System (ATCRBS). The transponderresponds to interrogations from TCAS equipped aircraft.ALT Selects Mode A, Mode C, and Mode S. Pressing the ALT key when the GTX 330 ispowered off automatically powers on the unit in altitude reporting mode.The transponderreplies to identification, altitude and Mode S interrogations as indicated by the reply symbol(®). Replies to altitude interrogations include the standard pressure altitude received froman external altitude source, which is not adjusted for barometric pressure.IDENT Pressing the IDENT key activates the Special Position Identification (SPI) Pulse for 18seconds, identifying the transponder return from others on an air traffic controller’s screen.During the IDENT period, the word “IDENT” appears in the upper left corner of the display.VFR Sets the transponder code to the pre-programmed VFR code selected in Configuration mode(Set to 1200 at the factory). Pressing the VFR key again restores the previous identificationcode.NOTEThe VFR key is on (functional) by default, but can be disabled in configuration mode.FUNC Changes the page shown on the right side of the display. Display data includes pressurealtitude, flight time, altitude monitor, count up, and count down timers. In theConfiguration mode, steps through the function pages.
