GTX 335 aviation surveillance device

The Garmin GTX 335 is a Mode S transponder with 1090 MHz ADS-B Out for aircraft surveillance, produced by Garmin. It replies to ATCRBS Mode A and Mode C interrogations and to Mode S interrogations, and it broadcasts extended squitter reports so that air traffic control and nearby aircraft receive identity, position, altitude, velocity and climb or descent information.

The ADS-B Out function uses the 1090 MHz extended squitter datalink. Position data come from an optional built-in GPS/WAAS receiver, or from an external GNSS source, and the transmitter is solid state with a minimum transmit power of 200 W. Pressure altitude can be supplied by an optional Garmin altitude encoder module that mounts on the connector backplate, which keeps the static line connected when the transponder is removed from the rack. The maintenance manual describes optional internal GNSS and an optional altitude encoder for the GTX 335 family.

Electrical and environmental data are useful for installation planning. The supply range is 14 or 28 VDC, with a maximum power of 15 W at 14 V and 17 W at 28 V as listed by the maker. The manual gives a typical input current of 0.57 A at 14 VDC and 0.29 A at 28 VDC for the unit without GPS, and a maximum of 0.86 A and 0.43 A. The operating temperature range is from -40 C to +70 C, the operating altitude reaches 55,000 ft (16,800 m) and no cooling air is required. The unit measures 42 x 160 x 256 mm including rack and connectors and weighs 1.27 kg (2.8 lb), or 1.32 kg (2.9 lb) with the optional parts.

The unit communicates through ARINC 429, RS-232, Gray code and discrete I/O. Antennas are connected to the bottom of the fuselage, and the diversity version, the GTX 335D, adds a second antenna on top. The panel-mounted version has an integrated display, push-button squawk entry and a pressure altitude readout, and fits a standard 1.65-inch high slot. Remote-mounted versions work with compatible displays and control sources, including GTN 650 and GTN 750 units and select G1000 systems.

On approvals, Garmin lists TSO-C88b (with the optional altitude encoder), TSO-C112e (Class 1, Level 2els) and TSO-C166b (Class B1S) for the panel-mounted version. Environmental qualification follows DO-160G, software follows DO-178 Levels B, C and D, and hardware follows DO-254 Level C.

Typical applications are certified general aviation and light utility aircraft that must meet ADS-B Out equipage rules, and larger crewed or optionally piloted aircraft platforms that need a certified Mode S and ADS-B Out transponder in the standard avionics stack format.