Garmin diversity transponders OK'd

Diversity means that the systems support a transponder on top of the aircraft, which is optimal for satellite reception of the relatively low-power ADS-B signals, as well as the traditional belly-mounted antenna. Garmin received the FAA STC in conjunction with Transport Canada Civil Aviation (TCCA) and European Union Aviation Safety Agency (EASA) validation.

Nav Canada surprised many when, in a January 2019 webinar, it announced that it would require 1090ES ADS-B Out transponders with antenna diversity in certain airspace. Nav Canada, an owner and the lead air navigation services provider in the Aireon space-based ADS-B service, will use the Aireon ADS-B payload aboard every Iridium NEXT communication satellite for space-based ADS-B air traffic surveillance. It had shared little information with general aviation operators in Canada to support the requirement for diversity. In March the industry challenged the diversity mandate, and in November Nav Canada postponed the mandate—not because it won’t be needed, but because regulator Transport Canada required a rulemaking process.

Canada’s air navigation service provider in January revealed that as early as January 2021, it would require 1090-MHz extended squitter (1090ES) ADS-B Out system with antenna diversity, meaning top and bottom transponder antennas, to facilitate data reception by satellites.

Nav Canada finally shared some satellite ADS-B reception data, which matches findings by the FAA and other agencies—that satellites cannot receive data from belly-mounted antennas alone with enough reliability to meet performance requirements. The FAA has indicated satellite-based ADS-B may be the next step in ADS-B’s evolution, enabling surveillance in oceanic airspace and other places where ground infrastructure is impractical or impossible.

“We’re still exploring what might be possible with space-based ADS-B, but it is clear that there could be considerable compatibility issues for the majority of general aviation,” said Rune Duke, AOPA senior director of airspace, air traffic, and aviation security. “Aireon’s system is doing as it was designed. It is an effective solution for high-altitude, offshore, non-domestic airspace where there is a lack of surveillance and a high percentage of diversity-equipped aircraft, like airliners and business aviation. Besides the antenna reception concerns, general aviation is also looking for FIS-B and TIS-B benefits that are reliant on a ground-based ADS-B network.”

Garmin’s two new diversity products significantly expand options for GA operators. The GTX 335D offers ADS-B Out, while the GTX 345D also adds dual-link ADS-B In traffic and weather for display on compatible avionics and mobile devices. Remote-mount versions are also available.

The company said the GTX 335D and GTX 345D transponders are intended for qualifying aircraft that may prefer or require a diversity solution, while also meeting or exceeding global ADS-B airspace requirements. In addition to better satellite conspicuity, Garmin said diversity antennas help reduce antenna shading caused when the aircraft turns or maneuvers, improve line-of-sight visibility, and allow the transponder to more robustly send and receive ADS-B transmission from other participating aircraft.

The GTX 345D provides additional capabilities, displaying Flight Information Services-Broadcast weather and dual-link ADS-B traffic on compatible cockpit displays, Garmin portables, and mobile applications. It also may be integrated into the aircraft’s audio panel to provide ATC-like audible traffic alerts.

Garmin said the GTX 335D and GTX 345D are available immediately, with suggested retail prices of $6,495 and $7,995, respectively. For additional information, visit the Garmin website or contact a Garmin dealer.