Updated: Dec 30, 2020
WAAS greatly increases the reliability and accuracy of GPS Satellite position reporting.
Here's what you need to know.
HOW IT WORKS
WAAS stands for Wide Area Augmentation System and is the FAA's way of correcting GPS Satellite errors and relaying that corrected information to pilots in flight.
Non-WAAS GPS Units can experience errors up to 300' both laterally and vertically. However, WAAS enabled GPS Units cut that error down to 6-9' both laterally and vertically.
Here's how it's done.
We will be discussing the systems depicted in the diagram below.
THE GPS SATELLITES
Notice there are 2 different types of satellites in our diagram: GPS Satellites and Geo-Stationary Satellites (which will be discussed later).
The GPS Satellites are what relay position information to our airplane as well as cars and mobile phones. They are controlled by the DOD (Department of Defense).
THE MONITORING STATIONS
The FAA has built Monitoring Stations in different locations across the United States. These Monitoring Stations are cemented to the Earth and have a fixed latitude and longitude.
These stations monitor the information being relayed by the GPS Satellites. The information they receive is then relayed to one of multiple WAAS Master Stations.
THE MASTER STATIONS
Master Stations receive information from the Monitoring Stations and make the necessary mathematical corrections to position data (if necessary). Since the Monitoring Stations have a fixed latitude and longitude, it is easy to make these calculations to correct any incorrect data being received.
THE UPLINK STATIONS
The Master Stations then send corrected GPS Position Data to one of multiple Uplink Stations. These stations then forward that corrected information to the 2 Geo-Stationary Satellites (these are not the original GPS Satellites but 2 separate ones).
THE GEO-STATIONARY SATELLITES
They are called Geo-Stationary Satellites because they are located over the Equator and spin at the same speed as the Earth's rotation. This means they are always positioned over the same geographical locations of the Earth.
One is stationed over the West Coast of the United States and the other is stationed over the East Coast.
These satellites are then able to send the corrected GPS Position Data to the GPS Units aboard our aircraft. Hence, the pilot has reliable and accurate position information.
In short, the WAAS system: Monitors GPS Data, Corrects Errors, Uplinks Data to Geo-Stationary Satellites, and forwards that corrected information to aircraft in flight.
Author - Nate Hodell
CFI/CFII/MEI/ATP - Creator of wifiCFI - Owner of Axiom Aviation Flight School.
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