Which system improves GPS accuracy required for precision approaches?

WAAS, or Wide Area Augmentation System, is the correct choice for improving GPS accuracy required for precision approaches. This system enhances the accuracy of GPS signals, providing critical corrections that allow for more reliable navigation, especially during approaches and landings.

WAAS achieves this by utilizing a network of ground reference stations that monitor GPS satellites and collect data on their signals. This data is then used to compute corrections for potential errors and is transmitted to geostationary satellites. Aircraft equipped with WAAS-capable GPS receivers can then receive these corrected signals, which significantly increases the precision of GPS positioning, making it suitable for precision approaches.

In contrast, while RAIM (Receiver Autonomous Integrity Monitoring) also enhances GPS performance by monitoring the integrity of the signals received from satellites, it does not provide the same level of accuracy improvements as WAAS. GBAS (Ground-Based Augmentation System) is another method for improving GPS accuracy but primarily serves in specific airport environments rather than providing widespread coverage like WAAS. ADS-B (Automatic Dependent Surveillance–Broadcast) is primarily a surveillance technology that provides position information to air traffic control and other aircraft but does not directly enhance GPS accuracy.