For those with a smaller budget, Garmin’s GDL 39 is a great option. The GDL 39 is a portable ADS-B receiver that gets free ADS-B weather and ADS-B traffic too. The unit contains both a WAAS receiver and an ADS-B receiver. It connects to an iPad via a Bluetooth connection or to the Garmin 796 (with Bluetooth on the way) or GPSMap 696 and Aera 500-series handhelds via a dedicated cable. As far as iPad apps are concerned, the GDL 39 currently works only with Garmin Pilot, the company’s excellent all-in-one iPad app that gives you moving map, charts, weather, terrain alerting, airport and FBO info, and more. Making the connection was dirt-simple, and the performance of the GPS/WAAS ADS-B receivers was excellent. The GDL 39 sells for around $800 including accessories.
With the GDL 39 you can receive ADS-B weather transmissions when you’re in line of sight with an FAA ground station and display that weather on Garmin’s brand-new Garmin Pilot iPad app (more on that product in a bit). The weather, as we’ve written about before, is very good, though not quite as good as Sirius XM Weather. The big advantage of ADS-B weather is that you not only get most of the weather products you care about at reasonably good quality, but there’s no subscription, as there is for Sirius XM Weather, for instance. The downside is that, because it’s a ground-up system, you can’t always get reception. This is true for ADS-B weather in general, regardless of the receiver or whether it’s permanently installed or mounted or a portable unit. The weather you get with the GDL 39 is good, and the display of weather on Garmin Pilot on your iPad is excellent, with the weather information, animated Nexrad, graphical metars, winds and more shown on the main map page and also integrated into various airport information pages so you can check the weather without changing screens. The integration of ADS-B weather into Garmin Pilot is top-drawer.
Unlike a couple of competitors’ boxes, the GDL 39 provides in addition to weather ADS-B traffic information for display on the iPad or other devices. What traffic you will see varies tremendously based on a number of different factors, the most important of which is whether you are, to use the FAA’s term, participating in the ADS-B scheme. Those operators who get weather and traffic with ADS-B In (like with portable gear) but don’t transmit their ADS-B position information (ADS-B Out) don’t get the same benefits as participants get.
ADS-B as it stands today presents an incomplete traffic picture, and that’s the way it will stay until 2020. The picture, thanks to the FAA’s strange stance on providing traffic information, is far more confusing and incomplete than it needs to be. Because the feds are trying to encourage people to participate in ADS-B by installing ADS-B Out equipment, they have decided to not send traffic information via ground stations to airplanes with just ADS-B In, such as with a portable system like the GDL 39. To the many critics of the plan, the withholding strategy seems at worst a hazardous gamble designed to strong-arm operators into equipping, a plan that intentionally keeps critical and freely available safety data away from pilots. As a result of the FAA’s arbitrary restrictions, not to mention the small numbers still of ADS-B participants, it’s impossible to tell when you’re going to see traffic, if there’s traffic out there you’re not seeing, or whether the traffic you’re seeing is going to disappear just as suddenly as it appeared.
If you’re not yet participating, you’re going to get air-to-air traffic, so if there’s another ADS-B target, it will show up on your display. In our test of the GDL 39 at altitude, this function worked perfectly. When using the GDL 39 in a CJ, we didn’t see traffic that would normally be relayed through the ground station, because we were not participating (by having ADS-B Out).
There are a couple of other types of traffic you’ll get with ADS-B In only: If you pass near a participating ADS-B target, you’ll get traffic data from the ground station that that target is “lighting up.” But once you lose sight of that target, you lose sight of all the traffic it was sending along to you as well.
On our flight, for instance, we were passing near a 757. The pilot was getting traffic from the ground station he was in contact with. We could see that traffic through our portable ADS-B receiver, including nonparticipating ADS-B airplanes that are near a ground station (around 15 miles and plus or minus 3,500 feet from our altitude), but once we lost “sight” of the 757 we lost sight of all of his relayed traffic too.
