That’s presuming it’s installed correctly and up-to-date. So if your non-WAAS GPS is certified for IFR to the approach level-and a Garmin 430 is-you can use it for IFR and for training. It’s accurate enough for a non-precision GPS approach. Practically speaking, 30 meters of accuracy is more than enough to fly from Airport A to Airport B even in the clouds. That correction might increase accuracy 10 fold, so the location is accurate to within 3 meters. These corrections are continuously updated by ground stations and relayed through the GPS system. WAAS is one form of Differential GPS, which means the GPS receiver uses the satellites and then applies a correction appropriate for that calculated location. For any given spot on earth, the accuracy of that position varies from day to day but is usually within 30 meters or less. Technically, a non-WAAS GPS relies solely on the transmissions from the GPS satellites for its position.
“There are really three parts to the answer: What’s the technical difference, what’s the practical difference, and why do you care?
