WAAS Made Easy


It seems that every bit of new aviation technology is initially made much more complicated and confusing for pilots to use than is necessary. For example, when GPS navigators first became available, every instructional course from the FAA or others would start out describing the constellation of GPS satellites, their orbital altitude and so on. Who cares? And what, as a pilot, can you do about those satellites anyway?

When GPS approaches were approved we all were bombarded with descriptions of and warnings about RAIM, or the lack of it, at our destination. As I recall, RAIM stands for something like "receiver autonomous integrity monitoring." It has to do with how many GPS satellites are in view, and their relative angles which can affect the navigation solution. If RAIM is not available, an approach-approved GPS won't go into the active approach mode. But, again, there is nothing a pilot can do about RAIM.

And now we have WAAS-wide-area augmentation system-that enhances GPS accuracy and, equally important, improves the ability to monitor the integrity of the navigation guidance. By now just about every pilot must know that with a WAAS-capable GPS navigator it is possible to fly approaches down to the same visibility and decision height minimums as on a conventional ILS.

But as soon as a pilot installs a WAAS navigator, or converts his existing Garmin 430/530 to WAAS capability, the unnecessary confusion starts. And I blame the FAA and the instructor community for this problem, just as they caused the confusion about previously introduced new technology.

In one paragraph I have told you all you really need to know to put your new WAAS GPS system to work. The box itself, and the instrument approach chart, show you everything you need to fly approaches with WAAS, and they do it automatically with no need for additional training.

When we're talking WAAS and GPS we are really talking about Garmin and its 430/530 system. The company has delivered more than 90,000 of its GNS 530/430 navigators over the past few years, and it uses the same basic operating system in the all-glass integrated G1000 cockpit that dominates the new piston and light jet market. Garmin's equipment and operating methods rule the world of IFR flying in personal airplanes, and also in an ever-expanding list of utility and business aircraft. It is the system that sets the standard because of its numbers in the fleet.

This is how difficult it is to use a Garmin WAAS navigator to fly an approach. First you press the procedure button and a list of available instrument approaches at your destination airport appears. You place the cursor over the approach you want to fly, enter it, and that's it. You're ready to activate the approach and fly it. WAAS has taken care of itself.

Once the approach is selected, the 530/430 tells you what type of approach it is. Most RNAV approaches-what used to be called GPS approaches-will show up as lateral nav (LNAV), and many of those will also have vertical guidance. If the vertical guidance is available, the glideslope needle on your navigation display will automatically give you fly up or down commands just like an ILS. That's all there is to it.

Many, if not most, ILS approaches in the country have an RNAV approach overlaid. What I do with WAAS is select the RNAV approach on the number one system that is coupled to my flight director and autopilot, and then put the raw data ILS signal on number two. The RNAV approach guidance is so much smoother than most ILS signals that it is easier for me or for the autopilot to fly. And when you get close to the runway the RNAV "glideslope" stays perfectly smooth and stable all the way to the pavement, while the real broadcast glideslope starts to bounce around.

But what if the RNAV approach has the vaunted LPV status? Nothing changes. You simply select the approach in the normal way and fly the signal to the published minimums, which are typically lower than for a standard RNAV approach. Yes, there is a WAAS satellite channel number printed on the LPV approach plate, but so what? You can't select it. It is stored in the 530/430 database and you don't need to do a thing.

The LPV navigation display is designed to look more like the angular deviation indication of a real ILS, but that makes no difference in the way you fly it. And the decision height on an LPV approach means exactly the same thing as it does on a normal ILS, so there is nothing to learn there. The only difference you will see compared to a conventional ILS is how smooth the GPS-WAAS guidance is. You will see that many of those excursions left and right that we have blamed on our poor flying skills in the past are really bends and warps in the conventional ILS signal, and they are gone with WAAS.

However, there is one area of potential pilot confusion that is being blamed on WAAS, but actually results from the expanded lateral navigation capability that is part of the system, and that is the ability to fly an entire approach automatically. With a WAAS 530/430 or G1000 you can be guided precisely through a complete instrument approach procedure including any procedure turns, holds, DME arcs or other course changes that are part of the published procedure. The autopilot can fly the approach perfectly with the system computing turn anticipation so that it doesn't overshoot the next leg. It is a marvel to watch.

But here's the rub that is baffling many pilots and their instructors-you can't modify the procedure if you elect to fly it as published. When you select the desired approach, the navigator offers you the option of the full procedure or vectors to final. If you opt for the full procedure, that is what you will get with absolutely no shortcuts. The system won't allow you to skip a holding pattern, for example, if that is part of the published procedure. But many pilots get bored waiting for the airplane to automatically fly the complete procedure and then they-not the navigator-become confused when they try to make it jump ahead. Or they try to intercept an initial approach fix from outside the boundaries on the chart. Or they try to short circuit a procedure turn. It won't work.

On the other hand, if you select the vectors to final option, maneuvers such as procedure turns and holds will be eliminated and you can intercept the final for a straight in. I almost never fly full procedure approaches because so much of the country has enough radar coverage that controllers can at least point you toward the final course. I do fly full procedures in recurrent training, and usually we get tired of watching the simulator drone around a procedure, turn, hold or whatever, and that's when I try to intervene and confuse myself. Stay with a vectors to final approach every time you can, and life will be easy. When a full approach is necessary you must understand that a WAAS box will not skip a thing.

As for WAAS minimums on approach, it is obstructions, terrain and runway lighting that will determine how low you can go, not the precision of the guidance. On a typical RNAV approach you can follow the pseudo-glideslope until reaching minimum descent altitude (MDA), the same altitude you would descend to without the vertical guidance. If the runway isn't in sight, you can level at that altitude and continue until reaching the missed approach point, which is usually the runway threshold. On an LPV version of an RNAV approach the minimum altitude and visibility requirement will be lower than for an RNAV, but no new technique of flying or operating the navigator is required.

The great news about WAAS is that just about every instrument approach looks like an ILS, can be flown like an ILS, and you don't need to learn how to do any extra button pushing. I think we want to make this seem hard because it's really so easy.