Wide Area Augmentation System

WAAS, or Wide Area Augmentation System, is a navigation system with a high level of accuracy, used to provide additional help to Global Positioning Systems (GPS) for air navigation. It was developed by the Federal Aviation Administration, an agency of the United States Department of Transportation.

The main aim of WAAS is to improve the accuracy, integrity, availability, and continuity of GPS, so that pilots can rely on GPS during all phases of flight.

The three key segments of WAAS configuration are―

This consists of a number of Wide-area Reference Stations (WRS) that gather information on GPS signals, and transmit them to Wide-area Master Stations (WMS) through terrestrial communication networks.

WRS also keeps a tab on the signals of geostationary satellites of WAAS. The Master Stations make corrections in the data received from WRS sites, which is then sent from the Master Station to the Ground Uplink Station (GUS). The GUS broadcasts them to satellites in the Space segment.

The main task of the space segment is to transmit the rectified data generated by WMS to the user segment via multiple geosynchronous communication satellites. These satellites also carry out the functions of broadcasting range information like other normal GPS satellites. As a result, the number of satellites available for a particular position increases, which, in turn, improves efficiency.

The main component of the user segment is the GPS and WAAS receiver. It uses the information provided by GPS satellites and WAAS corrections from the space segment to ascertain the current location and the time of the aircraft.

WAAS provides a solution to almost all kinds of navigation problems. It gives precise information of position that is easy to use. It is obtained at the cost of only one receiver that is installed on the aircraft. Because of its ground and space-based infrastructure, the aircraft does not have to depend much on ground-based signals from airports.

WAAS can operate between airports too. As a result, it enables the aircraft to travel directly from one airport to the other. It can cut down distances to be traveled, thus saving time and fuel.

Aircraft equipped with WAAS can fly at lower altitudes, which is not possible with ground-based signals, as these signals may get blocked by varying terrain. On the other hand, WAAS gives all information through GPS satellites. This is helpful particularly for unpressurized aircraft, as it conserves oxygen and ensures safety.

Despite being an extremely effective system for air navigation, WAAS has its own share of problems too. The number of satellites and ground stations available for WAAS are limited. Due to this problem, the number of locations for which positioning can be calculated are just confined to specific points.

Also, aircraft need to be fitted with certified GPS receivers. These are costlier than other commercially available units. The accuracies required for ground-based landing instruments of smaller airports are not available in WAAS. So, either the aircraft needs to maintain the old ground-based equipment or the airports need to replace their systems with WAAS.