Ask My Sky Mom. Aviation wit and wisdom.

Hey Mom,

My question is this: what is WAAS? Is it a different kind of GPS, or is it something totally different? I don’t really understand what it is or if it’s something I even need to know to get started on my instrument rating.

Thanks,

Worried About WAAS

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Wassup, Worrier?

The skinny on the WAAS is that it’s an improvement of the existing GPS system. In fact, WAAS stands for Wide Area Augmentation System. GPS, as you probably know, is the Global Positioning System. A constellation of 27 satellites orbit the Earth, courtesy of the US Department of Defense. 24 of those are necessary, the last 3 are spares. Basically, the receiver you’re toting around in your airplane (or in your back pocket, whatever) picks up as many of these as it can and then triangulates your position based on that information. You need at least 3 of those bad boys to get a two dimensional location nailed down. 4 or more in sight can get you altitude information as well.

WAAS uses a network of 25 ground-based reference stations and 2 master stations to measure small variations in the GPS satellites’ signals. Measurements from the reference stations are routed to those master stations, which send the correction messages to geostationary WAAS satellites. Those satellites broadcast the correction messages back to Earth. The gist of all this is that the ground stations function similarly to additional satellites, meaning that you’ll be hard pressed to be out of range enough NOT to be able to get 3D info from the system wherever you happen to be. In North America. Eventually, WAAS capability should be worldwide, but for the moment, that’s all still up in the air. All these extra signals with additional corrections also improve the accuracy of the whole shebang. Bonus.

So why is everybody so excited about this? Consider this. Instrument approaches are designed to get you down nice and low, hopefully low enough that you can get below the clouds, right on top of the airport, so you can see enough to find your runway and make a nice landing. You know, the kind that doesn’t scare your passengers. Precision approaches are preferred as they give a pilot vertical navigation guidance as well as the lateral nav we’re all accustomed to. This lets a pilot get lower in most cases, and adds to the safety margin. Up until now, the equipment to do this has been expensive to install and maintain. GPS approaches already allow approaches at many airports that had none before the advent of satellite navigation. If, through the addition of WAAS, we can make many or most of those approaches into precision approaches, pilots have far more options, and pilots with options are happy pilots indeed. WAAS also gives us another tool to improve RAIM (Receiver Autonomous Integrity Monitoring), the GPS receiver’s self check that it’s getting adequate and accurate information on which to base the navigation solution.

WAAS that all you wanted to know?

Fly safe, and make sure that thing is certified for IFR before you start trusting it in the clouds,

Mom

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You’ve got questions? I’ll find you an answer. Email your aviation related question to mom@myskymom.com and check out myskymom.com to read the answers to questions previously posted. An educated pilot is a safe pilot is a happy pilot!  Read on, fly safe, and remember: the only stupid question is the one you didn’t ask!

~ by myskymom on October 12, 2009.