ADS-B vs. SiriusXM

Michael Leighton compares two popular portable units that can receive in-flight weather and more.

Perhaps the most significant safety improvement in aviation in the last 20 years is the availability of cost effective, quality, real-time weather and traffic in flight. Once found only on high-end corporate aircraft, real-time weather is now available to any pilot with an iPad using a portable receiver. The most popular portable options are the Stratus 2S ADS-B receiver from Appareo and the SXAR1 receiver from SiriusXM Aviation.

I did a side-by-side comparison of both systems with each receiver dedicated to one of two iPads. My test flights were conducted in a single-engine piston and a single-engine turboprop.

Similarities

Both receivers are small and lightweight. Both utilize rechargeable lithium-ion batteries with a life span that exceeds the average fuel leg in most General Aviation aircraft. The Stratus 2S has an eight-hour battery life, while the SXAR1’s battery life is up to six hours. In-flight recharging is easily accomplished with a USB cable, if necessary.

The light weight of both devices makes a suction cup window mount or a piece of Velcro on the glareshield two practical solutions for mounting the receiver. Both units are simple to operate, featuring exactly one button to turn the unit on or off.

Both units use indicator LEDs to identify which functions are operating and the status of the battery power. In flight, both receivers display weather in real time on an iPad.

I use ForeFlight in my cockpit, and both receivers are compatible with ForeFlight. Though some tech-savvy users claim to have made these receivers work with other apps, only ForeFlight is officially supported.

Differences

Though both units provide weather information, they do so in very different ways.

Stratus 2S and ADS-B

The Stratus 2S utilizes the government-developed Automated Dependent Surveillance Broadcast, commonly referred to as ADS-B.

ADS-B weather is ground-based and subject to line-of-sight limitations; that’s why it’s typically not available when the aircraft is on the ground. Additionally, there are “holes” where ADS-B reception is intermittent. Since ADS-B is the cornerstone of the Next Generation (NextGen) air traffic control, the FAA says that when the system is fully operational in 2020, any in-flight reception issues should be resolved.

Geographic coverage for ADS-B extends about 20 miles beyond the United States’ borders. On our trips to the Bahamas, we receive ADS-B coverage to about 30 miles offshore at 10,000 feet—our altitude and the lack of terrain obstructions allow the signal to reach farther.

The weather products available with ADS-B are adequate for the average General Aviation mission. When in flight, composite NEXRAD is available. Base reflectivity and cloud coverage are available on the ground using an internet connection, but not in the air.

Airborne ADS-B also provides METARs, TAFs, SIGMETs, AIRMETs, TFRs, visibilities, ceilings and flight conditions for graphic display and in text format; notams and Special Use Airspace alerts are also available.

ADS-B with the Stratus 2 includes features you cannot get from SiriusXM Aviation weather. Traffic and a backup PFD are phenomenal features provided by Stratus. I love the backup PFD. I teach my students how to shoot an approach with it in the event of a total equipment failure.

If your aircraft does not have a traffic avoidance system, ADS-B traffic is useful, but until 2020—when all aircraft are supposed to be equipped with ADS-B—it does not depict all traffic.

The best part of ADS-B is that the service is free, while SiriusXM uses a paid subscription. However, the receiver to get free ADS-B data can cost more up front: a Stratus 2S lists at $899, not counting any antennas. In contrast, an SXAR1 is priced at $699, and may qualify for a $200 rebate, but subscription fees will be extra.

SXAR1 with SiriusXM Aviation weather

The Sirius product, SXAR1, gets its data not from the ADS-B source, but from SiriusXM satellites. It also has a GPS/WAAS embedded receiver.

The SiriusXM aviation weather subscription includes the same weather products provided by ADS-B, as well as icing icing, winds aloft, lightning, in-flight base reflectivity radar, radar echo tops, cloud tops, turbulence and surface analysis. The range of coverage includes most of Canada, parts of the Caribbean, and extends much farther offshore.

A subscription for the SiriusXM Pilot For ForeFlight package is around $40 per month. More comprehensive weather information is available with Pilot Preferred ($59.99/month) and Pilot Pro ($99.99/month) packages. For all SiriusXM aviation weather packages, the ability to listen to your favorite music and news channels in flight, if you so choose, can be added to your weather subscription at a discounted rate.

One unexpected issue arose with the SXAR1 receiver during my testing. The electrically-heated windows in turboprop airplanes interfere with data reception. Moving the unit to an unheated side window improved my reception. Depending on which side of the plane the receiver was placed also affected the unit’s ability to receive data from the satellite. (We contacted SiriusXM and about this and received this reply: “Heated windscreens on some aircraft may block or interfere with the SXAR1 Receiver data reception. If you experience a weak signal condition, place the SXAR1 close to either side window or you may choose to purchase an optional External Antenna at shop.siriusxm.com or at sportys.com. The antenna can then be placed in the cockpit for best signal and the SXAR1 receiver can be placed out of the way.” —Ed.)

Another difference to address is the display resolution. The resolution is the same for the SiriusXM Aviation via SXAR1 and for ADS-B through the Stratus 2 when viewing weather within 200 nm of the aircraft. Beyond 200 nm, the resolution of the SXAR1 really shines; beyond that range ADS-B reduces the radar resolution, making the radar appear more coarse and pixelated. SiriusXM is consistent with its resolution at longer range.

Final thoughts

Do you have to choose one over the other? When flying with both units, you do not need to choose only one to use because SXAR1 connects because SXAR1 connects to your iPad with Bluetooth, while Stratus utilizes Wi-Fi. This means you can have both at the same time—on the same iPad. Playing with the displays of Stratus on the backup PFD and the SXAR1 shows the advantages of each; the advanced weather features and better range of the Sirius product and traffic on the Stratus.

Is SiriusXM worth $39.99 a month? It is to me. From my observations, I can say that I love SiriusXM Aviation weather. Since I regularly fly in real weather, the echo tops, icing and selectable winds aloft features make a difference for me. I love that the weather data is usually loaded and displayed before I take off. I do a fair bit of flying in the Bahamas and XM’s radar coverage, particularly when trying to cross the Gulf Stream, is very useful.

I have had SiriusXM weather in my plane for 12 years, but it is displayed on a Garmin 530. The limitations of the older Garmin devices preclude receiving all the benefits of the service. The portable SXAR1 unit coupled with an iPad allows a pilot to receive every benefit of the SiriusXM service. The value of in-flight real-time weather cannot be emphasized enough.

For the owner-pilot who must comply with the ADS-B mandate by Jan. 1, 2020, it is typically far less expensive to install an ADS-B Out-only transponder and buy a portable ADS-B In receiver than to purchase a combined ADS-B Out+In device. A portable receiver allows these operators to enjoy the benefits of ADS-B In—without the installed-in-the-aircraft cost.

In addition, the portability of the Stratus 2S and the SXAR1 are perfect for a pilot like me who flies several different aircraft.

The SXAR1 receiver delivers the most complete and comprehensive in-flight weather data available on a portable device. The safety features in the Stratus 2—especially after the ADS-B Out mandate takes effect—are phenomenal. I plan to carry both.

Michael Leighton is a 11,000-hour, three-time Master Flight Instructor and an A&P mechanic. He operates a Part 141 flight school in South Carolina and South Florida. You can find him on the web at flymkleighton.net. Send questions or comments to editor.