Plain English Meaning

The older, ground-based radio aids that pilots fly to and from -- like VOR stations and instrument landing systems -- as opposed to newer satellite navigation like GPS.

Full Definition

The collective term for the ground-based radio navigation aids that pilots have used for decades to determine position and track courses, principally NDB (Non-Directional Beacon) with ADF (Automatic Direction Finder) receivers, VOR (VHF Omnidirectional Range), DME (Distance Measuring Equipment), and (). These rely on radio signals transmitted from fixed ground stations and received by equipment in the , in contrast to such as GPS.