Announced at AirVenture last summer, the $1795 GDL82 (includes antenna) has Garmin’s signature smart engineering and even better, the simplest interconnect of any Garmin ADS-B product to date. The system is a remote transmitter that connects in-line between the existing
transponder and the transponder antenna system. See the installation sidebar on below for a pictorial.
It’s a practical interface that we wonder why it has taken years to develop. The patent-pending system is certified via an STC with a flight manual supplement on a Mooney M20 series, and Garmin authorizes installers (via STC authorization letter) to use the STC as a basis for signing off the GDL82 installation. It used to be that even with this previously approved data, shops had to lobby for FAA field approval. But according to Garmin, as long as the install is performed according to the STC installation manual, it can be signed off as a minor alteration by either a Part 145 repair station or an A&P holding an IA (Inspection Authorization) certificate. Based on our research, this is in line with the FAA’s March 2016 memorandum for guidance on the installation approvals for ADS-B Out systems. What does this mean for you? Less regulatory work for the installing shop means fewer labor dollars billed into the bottom line. The GDL82 is a smart box in the sense that it synchronizes with the aircraft’s transponder via 1030 MHz interrogations to obtain the transponder Mode 3/A squawk code, pressure altitude and Ident status. Garmin calls this Autosquawk and it’s used on other Garmin ADS-B products. Autosquawk eliminates the need for a separate ADS-B control head, something required for some low-cost L3 and Freeflight ADS-B systems. The GDL82 footprint is 3.39 inches wide, 1.48 inches high and 7.99 inches long, making it the right size for connecting in-line with the transponder antenna cable. The output goes directly to the transponder antenna. Since the device has a built-in WAAS GPS, it has input for an external GPS antenna, which is included with the system. It’s important to note that the STC does not provide data for the basis of airworthiness approval for the GPS antenna, but for unpressurized aircraft, this is easily signed off as a minor alteration. It’s possible to use an existing panel GPS navigator for inputting WAAS position to a version of the GDL82 that doesn’t have a built-in GPS, although Garmin makes little if any mention of it in its marketing materials. That’s because the GDL82 is really intended as a bare-bones ADSB solution for minimally equipped aircraft. Plus, the effort it might take to run RS232 serial data wiring from the panel GPS to the GDL82 could eat up any cost savings.
There’s only a $50 delta between the two systems. Still, compatible navigators include the GNS530W/430W units with version 5.30 or later software, GTN700/600 navigators with software 6.41 or later and the CNX80/GNS480 with software version 2.4 or later. The way we see it, money may be better spent on upgrading the transponder antenna system, or even the transponder itself. Ask your shop if the existing transponder antenna is worth keeping. For the best performance, we favor fiberglass blade-style L-Band antennas over the rod and ball
style. You might have to spend more money to upgrade an older system. The installation manual advises replacing the transponder cable/connectors with MIL-C-17 type F low-loss cabling because it might be required to pass the transponder ramp check in accordance with Part 43, appendix F performance criteria. Shortchanging the installation could mean limiting the service ceiling of the aircraft. The STC warns that while an existing transponder is a Class A (that is,with an operational ceiling greater than 15,000 feet), a degraded antenna system could limit its service ceiling to Class B standards, good only below 15,000 feet. The limitation must be documented with a panel placard and logged in the flight manual. Optional is a panel-mounted ADSB Out failure annunciator, warning that the ADS-B transmissions are inoperative. There’s also an anonymous mode switch, which allows the GDL82 to transmit a temporary address instead of the aircraft’s assigned ICAO 24-bit address, when the Mode A/C transponder is squawking 1200. These optional accessories might add several hundred dollars or more to the installation. The install manual says they have to be installed in a panel location so that the pilot has an unobstructed and undistorted view of the annunciator.