GPS navigation in aviation uses signals from satellites to help an aircraft know where it is, where it is going, and how to follow a planned route. GPS is part of a larger family called GNSS, which includes satellite systems from several countries. This matters because accurate position information lets pilots and flight computers navigate safely across oceans, mountains, cities, and runways.
Modern aircraft often combine GNSS data with onboard maps, instruments, and autopilot systems.
Key Facts
- GPS is one type of GNSS, and it uses satellites that broadcast time and position data.
- An aircraft needs signals from at least 4 satellites to solve for latitude, longitude, altitude, and receiver clock error.
- Distance to a satellite is estimated by d = cΔt, where c is the speed of light and Δt is signal travel time.
- RNAV allows aircraft to fly point to point routes using onboard navigation instead of flying only from ground station to ground station.
- WAAS and other SBAS systems improve GPS accuracy and integrity by sending correction and warning information.
- Groundspeed can be estimated by v = Δs/Δt, where Δs is distance traveled over the ground and Δt is elapsed time.
Vocabulary
- GNSS
- Global Navigation Satellite System is the general name for satellite navigation networks such as GPS, Galileo, GLONASS, and BeiDou.
- GPS
- Global Positioning System is the United States satellite navigation system used to determine position, speed, and time.
- Trilateration
- Trilateration is the method of finding position by comparing distances from several known satellite locations.
- RNAV
- Area Navigation is a method that lets aircraft fly desired paths using onboard navigation equipment rather than only following ground-based radio stations.
- WAAS
- Wide Area Augmentation System is a satellite-based system that improves GPS accuracy, reliability, and warnings for aviation users.
Common Mistakes to Avoid
- Thinking GPS satellites track the airplane, which is wrong because the aircraft receiver usually listens to satellite signals and calculates its own position.
- Using only three satellites in aviation calculations, which is wrong because a fourth satellite is needed to correct receiver clock error and improve a full 3D position fix.
- Confusing heading with track, which is wrong because heading is where the nose points while track is the actual path over the ground affected by wind.
- Assuming GPS is always perfect, which is wrong because signal blockage, interference, satellite geometry, and equipment failures can reduce accuracy or availability.
Practice Questions
- 1 A GPS signal travels at about 3.00 x 10^8 m/s and takes 0.070 s to reach an aircraft. Estimate the satellite distance using d = cΔt.
- 2 An aircraft flies a GPS direct route of 540 km in 1.5 h. Calculate its average groundspeed in km/h using v = Δs/Δt.
- 3 A pilot notices that the aircraft heading is 090 degrees but the moving map track is 080 degrees. Explain what this difference suggests about wind and why GPS track is useful.