Instrument Rating Checkride Practice Test

What is the role of ground reference stations in the WAAS system?

1. To provide altitude corrections

2. To collect and correct GPS data

3. To facilitate communication with aircraft

4. To enhance VOR signal integrity

The correct answer is: To collect and correct GPS data

Ground reference stations play a crucial role in the Wide Area Augmentation System (WAAS) by collecting and correcting GPS data. These stations are strategically positioned to monitor GPS satellite signals and measure any discrepancies between the satellite positions and their actual positions. By observing the differences in these positions, ground reference stations can determine the errors in the GPS signals, such as ionospheric delays, satellite clock errors, and other inaccuracies. Once the ground reference stations process this data, they send the corrections to a central processing facility that computes the necessary adjustments. This information is then transmitted to geostationary satellites, which broadcast the correction data back to WAAS-equipped aircraft. This system improves the accuracy, reliability, and integrity of GPS navigation, making it much more suitable for critical aviation operations, like precision approaches to landing. In contrast, the other options address functions not performed by ground reference stations within the WAAS framework: there are no altitude corrections specifically handled by these stations, while aeronautical communication with aircraft is typically managed through other means, and VOR (VHF Omnidirectional Range) signal integrity is unrelated to the functions of the WAAS.