By now, pilots are well used to flying with a mobile device such as a portable electronic flight bag (EFB), and many pilots also carry a portable ADS-B in receiver that integrates with their mobile apps. While many aircraft are being equipped with ADS-B out, which will be mandatory after Dec. 31, 2019, there is no mandate for ADS-B in, and thus portable receivers are a good way to try out benefits of ADS-B in without an additional avionics investment.

While there are a variety of receivers available that work with many EFB apps, some are designed exclusively for one particular app, such as Appareo’s Stratus 1S and 2S for ForeFlight Mobile and Garmin’s GDL 39 series for Garmin Pilot. I’ve been flying with the Stratus 2S and ForeFlight for a few months to see what it is like to use these products regularly. The Stratus 2S is Appareo’s top-of-the-line ADS-B in receiver and it retails for $899. 

The Stratus 2S is Appareo’s most expensive receiver because it has not just ADS-B in traffic and weather but also built-in attitude and heading reference system (AHRS) sensors, a pressure altitude sensor, dual-band ADS-B in traffic and a Waas GPS receiver. The $549 Stratus 1S for doesn’t include the AHRS sensors and offers single-band traffic. Both can record flight parameters, including GPS position, altitude speed and attitude, which can be replayed later in Google Earth or CloudAhoy.

ForeFlight’s synthetic vision display and attitude indicator is greatly enhanced with the Stratus 2S’s AHRS, offering an excellent backup system in the event of major avionics/electrical or vacuum system failures. The AHRS automatically aligns, so there’s no need to make any calibration adjustments after suction-cupping the Stratus to a cockpit window.

Traffic Information Display

While it’s great to have quick access to the FAA’s free ADS-B in FIS-B weather products, the feature that makes the Stratus 2 most useful is the traffic. I’ve flown with the Stratus mostly in airplanes equipped with an active traffic system (either Tcas or TAS), and there is a difference between the information available on a Tcas or TAS display compared to ADS-B traffic, which is more accurately depicted. It should be noted that only Tcas II can issue resolution advisories and ForeFlight correctly warns, “Traffic display features may not show all aircraft in the area and are not to be used as a primary means of aircraft visibility detection or avoidance.” Nevertheless, I find that the position, altitude and velocity information provided for ADS-B in traffic is much easier to interpret, and I think it’s easier to spot traffic visually after seeing it on the ADS-B in display on ForeFlight than on TAS/Tcas.

The Stratus 2S is dual-band, meaning it receives both ADS-B out frequencies (978 and 1090 MHz) and thus can detect aircraft transmitting on both those frequencies. ForeFlight draws traffic with various symbols to highlight information about the target. For example, stationary targets (or targets without speed or direction information) are shown as diamonds, with blue indicating airborne traffic and brown ground traffic. A relative altitude number shows the difference between the host (my) aircraft and the target aircraft’s altitude, although this can be off by a few hundred feet because ForeFlight uses GPS-based altitude while some traffic data uses pressure altitude, another good reason not to rely on this information for separation purposes. ForeFlight adds a TargetTrend vector to show the speed of the target; the longer the vector, the faster its relative speed. When a target is climbing or descending faster than 500 fpm, a plus or minus sign and an up or down arrow is depicted. Finally, tapping on any target reveals additional information, which can include altitude, heading, speed, transmitting frequency and tail number.

In all the general aviation airplanes I’ve flown with the Stratus 2S, I’ve never had trouble receiving the ADS-B ground stations, including a long trip in a Phenom 300 at altitudes up to FL430. In the Phenom, the Stratus 2S easily picked up other airplanes, and its internal antenna latched onto ADS-B ground stations from 50 nm away. The only time I found the Stratus didn’t work too well at picking up ground stations was when trying to use it in an airline window seat, but holding it below and not on the window (so as not to cause concern to other passengers who don’t understand why I’m carrying a small rectangular device with blinking lights).

The Stratus receivers can be plugged into external power, but their internal batteries last for about eight hours. I’ve never used up the batteries in one flight. There is no physical limit to how many mobile devices can connect to Stratus receivers via Wi-Fi.

One other useful feature is a pop-up reminder when the cabin altitude passes through 12,000 and 25,000 feet, using the Stratus 2S’s built-in barometric sensor. The user can select audible or visual warnings or both.

Once you get used to flying with an ADS-B in receiver, you’ll never want to leave it at home. While the Stratus and other portable ADS-B in receivers can detect traffic via air-to-air signals anywhere in the world, the FAA’s free FIS-B weather and TIS-B traffic (broadcast from ADS-B ground stations) is available only in the U.S. Synthetic vision is available for the U.S. (including Alaska and Hawaii), Canada, the Caribbean, Mexico and Central America.