Non-directional beacon (NDB)

A special radio station, the emissions of which are intended to enable
a mobile station to determine its radio bearing or direction with reference to that special radio station.


That period of time between the end of evening civil twilight and the beginning of morning civil twilight.

Navigation specification1***sub***RNAV specification

A navigation specification based on area navigation that does not include the requirement for performance monitoring and alerting, designated by the prefix RNAV, for example RNAV 5, RNAV 1.

Navigation specification

A set of aircraft and flight crew requirements needed to support performance-based navigation operations within a defined airspace. There are two kinds of navigation specifications:


The National Aeronautical Information Processing System, which provides briefings and flight notification functions.

Hot spot

A location on an aerodrome movement area with a history or potential risk of collision or runway incursion, and where heightened attention by pilots/ drivers is necessary.