Waypoints: The WAAS factor

The Wide Area Augmentation System itself is a marvel of engineering. Thirty-eight reference stations around the country, plus two masters and a backup, sit on precisely measured sites. Sensors there know exactly where they are, and they compare that position to the ones they receive from the constellation of GPS satellites—then account for small errors that may result from atmospheric or other interference. The ground stations send the corrected information to the master stations, which send the corrections up to three geostationary satellites. Those satellites broadcast the corrections on a frequency near the one used by the GPS satellites themselves. Your WAAS-enabled receiver uses the correction factor to further refine your position information, providing a more precise position than the raw GPS signal.

That position can then be broadcast by your ADS-B Out system to let ATC and others know where you are.

That same WAAS precision allows us to shoot localizer performance with vertical guidance (LPV) approaches to Category I minimums at hundreds of airports that in the past did not have any approaches, or perhaps none with minimums that low. According to the FAA, there are 3,400 LPV approaches available. A great advantage of LPV approaches is that, aside from some approach lighting systems, no ground infrastructure is necessary at the airports. The signals are all space-based, saving installation and maintenance costs for the FAA. Some 80,000 aviation users take advantage of WAAS, which has been in service since 2003.

While the system all works great, it’s also expensive for the end user. The FAA insists that the GPS receivers used as an ADS-B position source and for instrument procedures be certified to a very high level and that they have integrity monitoring to alert the pilots within six seconds if the position accuracy is in doubt. All of that adds to the cost of development and manufacturing. Meanwhile, we’re all carrying around in our phones, cars, tablet computers, and other devices non-certified WAAS receivers that do a marvelous job of letting us know where we are and helping us get around—on the ground.

The FAA says those positions are not good enough for approaches and for separating aircraft. And they’re probably right regarding the approaches. When you’re approaching the ground to within 200 feet while in the clouds, you want a reliable and highly accurate position source that alerts you to any errors.

The debate becomes whether that level of accuracy is necessary for separating aircraft that typically are no closer than five miles apart in flight when on an IFR flight plan. The FAA says accuracy is necessary because in the future, it plans to fly aircraft closer together, improving the efficiency of the burgeoning airspace system. In addition, ADS-B is also meant to separate aircraft on the ground where airliner wing tips may pass within a few feet of each other on a foggy day at LaGuardia.

Despite the debate, the agency has not budged on its insistence that approved ADS-B systems use a certified WAAS receiver or its equivalent. So if you’ve wondered why ADS-B Out solutions cost as much as they do, that’s part of the reason.

The good news is that with the encouragement of AOPA, the FAA and manufacturers over the past four years have worked collaboratively to introduce products that meet the standard but do so at prices a fraction of what they were five years ago. Instead of starting at $5,000 just for the equipment, today you can buy it starting at $1,800. The complexity of the installations has come down as well. And, if you invest another few hundred dollars, you can get an ADS-B In receiver that gives you weather and traffic in the cockpit, further improving the value equation.

Keep in mind that if you don’t fly in airspace where a transponder is required today, you don’t need to equip with ADS-B to meet the 2020 mandate. However, to be detected by other nearby aircraft and to get reliable traffic information yourself—a great safety aid—consider making the investment. More than 44,000 GA airplanes were equipped with ADS-B Out as of August 1. I have talked to no aircraft owners who regretted the investment.

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