190-00734-11
GTX 33X and GTX 3X5 ADS-B Maintenance Manual
Rev. 6
Page 3-5
3.2 GTX 335/345
Figure 3-2 GTX 335/345 Front Panel
Function Selection Keys
The function selection keys are:
OFF
Powers off the GTX 3X5.
STBY
Selects the Standby mode. Pressing the
STBY
key when the GTX 335/345 is powered off
automatically powers the unit on in standby mode. When in Standby mode, the transponder
does not reply to interrogations but new codes can be entered and a SBY indication appears
on the display.
ON
Selects the On mode, which generates Mode A and Mode S replies, but Mode C altitude
reporting is inhibited. Pressing the
ON
key when the GTX 335/345 is powered off
automatically powers on the unit in Mode A and will transmit a squawk code when
interrogated. ADS-B Out will not return barometric altitude as it switches to GPS altitude in
this mode. Interrogations are indicated by the reply symbol (R). The replies do not include
altitude information.
NOTE
If the transponder is in the ON or ALT operating mode, the transponder becomes an active
part of the Air Traffic Control Radar Beacon System (ATCRBS). The transponder
responds to interrogations from TCAS equipped aircraft.
ALT
Altitude mode is automatically selected when the aircraft becomes airborne using the unit’s
air/ground logic or when the
ALT
key is pressed. Pressing the
ALT
key when the
GTX 335/345 is powered off automatically powers on the unit in altitude reporting mode.
While the aircraft is on the ground and in ALT mode, the transponder does not allow Mode
A and Mode C replies, but it does permit acquisition squitter and replies to Mode S
interrogations.
While the aircraft is in ALT mode and airborne, it will generate Mode A, Mode C and Mode
S replies as well as transmit acquisition and extended squitter, including ADS-B Out.
All transponder interrogations are indicated by the reply symbol (R).
IDENT
Pressing the
IDENT
key activates the Special Position Identification (SPI) Pulse for 18
seconds, 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 identification
code.
