How does GPS work and what is its accuracy for aviation use?

GPS (Global Positioning System) uses signals from a constellation of 24+ satellites to determine position through trilateration. Receivers measure time delay from multiple satellites (minimum 4 for 3D position plus time correction) and calculate position. Standard GPS accuracy is approximately 5-10 meters horizontally. Aviation applications use: WAAS (Wide Area Augmentation System) for 3-meter accuracy, enabling precision approaches; and GBAS (Ground Based Augmentation) for CAT II/III approaches. GPS provides position, velocity, and time, enabling RNAV (area navigation) independent of ground-based navaids.