Recently, a number of my customers have been asking me lots of questions about updating avionics. One of the main questions I get is “Should I get a WAAS GPS?” To me, it’s kind of a loaded question as it depends on your mission. When you’re buying an aircraft, you want to purchase an aircraft that accomplishes eighty percent of your mission. Well, in my opinion, you should do the same with your avionics.
First, let me explain what WAAS is. WAAS stands for Wide Area Augmentation System. It’s an air navigation aide created by the FAA to improve upon the current GPS constellation. The intention of WAAS was to allow pilots to be able to rely on their GPS through out all phases of flight.
There are three essential segments of WAAS. They are the Ground, Space, and User segments.
The Ground is a network of ground based stations that monitor and collect GPS signals that are sent to three Master Stations.
The Space segment is made up of a multitude of constellations of satellites.
The User is the actual units in each aircraft.
How it all works together simply is the Space segment sends out a signal and the User segment receives these signals and and implements them in the GPS unit to determine it’s location. The Ground segment monitors all these signals to verify accuracy. At least four satellites are needed for WAAS to work. With four satellites, you have three satellites for triangulating position and one satellite to verify signals. If you lose one of the satellites signals, you essentially lose WAAS capability.
Now you’re asking, why does this matter to me when purchasing a unit? I’m getting to it. Like I’ve said earlier, WAAS increases accuracy. Your WAAS GPS unit brings you to within 25ft as apposed to over 32ft with a non-WAAS unit. Big deal right? Well, when I’m flying in the “soup”, I’d rather have all the accuracy I can possibly have. The other benefits of a WAAS unit are lower approach minimums and a glide slope at airports that are equipped for WAAS approaches. When I say lower minimums, at most airports with a WAAS approach, the minimums on these approaches are lowered to approximately 200-250 feet AGL. Most of the time this is anywhere from 200-300 feet lower than your normal GPS approach. This is where I get back to my question of “what’s your mission?” comes back up.
Are you the weekend warrior that might shoot two approaches a year if you absolutely have to? Or are you using your aircraft for business and need to get to where you’re going more than the normal weekend trip? If you’re the first pilot, WAAS is probably not for you. You’re not going to use it or use it enough to warrant the cost.
Now if you’re not the second pilot you also need to think about it. The benefits of WAAS might not be in your budget. I’ve talked to a couple of local shops here in Texas and to get a Garmin 430W installed in most small GA aircraft, you’re looking at about $11,000. To get a Garmin 530W, you’re looking at about $15,000. Again you need to figure out how much you’re going to use the equipment to see if you can justify the cost. The newer units are going to be more expensive to have installed but are also going to give you a better platform for future advancements in avionics.
My personal opinion is I would put a WAAS unit in every aircraft if I could. I think it adds an extra safety factor and gives a pilot one extra option when making a flight. Please don’t confuse my words as telling a pilot to push the limits of an aircraft. With the proper training most pilots can handle any situation requiring WAAS.