How a VOR works
A VOR transmits a reference and a rotating phase signal. The receiver compares them to determine which of 360 radials the aircraft is on. Range is line-of-sight, so coverage improves with altitude.
GNSS
GPS receivers trilaterate position from at least four satellites — three for position and one to solve clock error. Augmentation systems such as EGNOS or WAAS refine accuracy enough for vertically guided approaches.
Redundancy
Airliners blend GNSS, inertial reference and radio navigation. If satellite signals degrade, the inertial platform coasts and the FMS reverts to radio updating.
Key points
- VOR indications are unaffected by wind or heading — they show radial position only.
- GPS needs four satellites in view for a 3D fix.
- Airliners fuse GNSS, IRS and radio navigation for integrity.
Knowledge check