Plain English Meaning

A radio beacon on the ground that sends out a signal in every direction. An aircraft instrument can sense which direction the signal is coming from, so the pilot knows which way the station is.

Full Definition

A ground-based, low or medium frequency radio transmitter that broadcasts a signal equally in all directions, allowing a suitably equipped aircraft to determine its bearing to or from the station using an Automatic Direction Finder (ADF) receiver. NDBs are used as enroute navigation aids, as approach aids for non-precision instrument approaches, and as compass locators with .