Garmin Adds AHRS Sensor to GDL 39 3D ADS-B Receiver

 - March 3, 2014, 4:10 AM
During an in-flight test of Garmin’s GDL 39 3D, the device delivered AHRS information to Garmin Pilot running on an iPad, shown here next to the attitude indicator in the airplane.

Garmin has joined the competition for AHRS-equipped portable ADS-B receivers with the new GDL 39 3D, priced at $849 or (with an optional battery) $899. Unlike other portable ADS-B receivers with built-in attitude and heading reference systems (AHRS), the GDL 39 3D works only with Garmin’s Pilot iPad and Android apps and most Garmin portable GPS receivers. When the GDL 39 3D is paired with the latest version of Garmin Pilot, users can view not only datalinked traffic and weather but also an AHRS-driven attitude indicator. The GDL 39 3D also contains a Waas-capable GPS receiver.

The AHRS sensor in the GDL 39 3D features plus or minus 500-degree-per-second three-axis rate gyros, 8-g accelerometers and a 2-gauss magnetometer. The GDL 39 3D communicates with Garmin Pilot via Bluetooth, up to two devices at a time, and can be simultaneously hardwired to a third (such as a portable Garmin GPS).

The ADS-B receiver works on both ADS-B in datalink frequencies, 978 and 1090 MHz, to receive traffic information service-broadcast (TIS-B) traffic information (traffic tracked by radar and broadcast by the FAA) and traffic from aircraft equipped with ADS-B out transmitters, although those are still relatively rare.

In the GDL 39 3D Garmin has incorporated TargetTrend technology, which tracks relative motion of traffic, and Surf, which helps display ADS-B-equipped targets on the airport surface. According to Garmin, “In dense traffic environments and in many other scenarios, TargetTrend allows the pilot to easily discern the aircraft presenting the greatest threat, which saves time and reduces workload.”

The 978-MHz datalink receives free flight information service-broadcast (FIS-B) weather information, which includes Nexrad imagery, Metars, Tafs, winds and temperatures aloft, pilot reports, notams and more. Traffic and weather data is stored in the GDL 39 3D as soon as it is switched on for quick delivery to the display unit (Garmin pilot on a tablet or a Garmin portable GPS receiver).

During a recent flight with the GDL 39 3D, the attitude indicator on the split window in Garmin Pilot, which was receiving pitch and roll information from the AHRS, perfectly matched the attitude indicators in the airplane that I was flying. The GDL 39 3D doesn’t have to be positioned on a level surface as it automatically levels itself when switched on, but it does have to be oriented in the right direction. While Garmin cautions that the AHRS-derived attitude information is only “an aid and should not be used as a primary attitude indicator,” it seemed suitable as a backup in case of loss of all other attitude information in the instrument panel.

For use in aircraft with heated windshields and that fly at high altitudes, the GDL 39 3D can be attached to an external GPS antenna and a belly-mounted external ADS-B antenna.