An aerodrome traffic zone (ATZ) is defined as: An airspace of defined dimensions established around an aerodrome for the protection of aerodrome traffic.
This definition is used in ICAO Annex 2 "Rules of the air" and Regulation (EU) No. 923/2012 "Standardised European Rules of the Air (SERA)".
The ATZ is intended to protect the aerodrome traffic, i.e. the traffic on the manoeuvring area and the traffic in the immediate vicinity of an aerodrome. This includes, but is not limited to, the aircraft in the aerodrome traffic circuit. There are no worldwide-accepted definitions about the size of ATZs in terms of lateral or vertical limits. Generally, the ATZ is considered to be a "small-volume" airspace, usually a cyllinder extending from the surface up to a few thousand feet with a radius of a few miles. The centre of the ATZ may be the aerodrome reference point (ARP), the centre of the (longest) runway, or another suitable point.
The airspace within the ATZ may be either controlled (and served by an aerodrome control tower) or uncontrolled (in which case e.g. aerodrome flight information service (AFIS) is offered).
The precise form and dimensions of the ATZ may vary from country to country. For instance, the following policy is adopted in the UK:
A zone extending from the ground up to 2000 feet with a radius of 2.5 NM around the midpoint of the longest runway for aerodromes where the longest runway is longer than 1850 m.
A zone extending from the ground up to 2000 feet with a radius of 2.0 NM around the midpoint of the longest runway for aerodromes where the longest runway is shorter than 1850 m.
A zone extending from the sea level up to 2000 feet with a radius of 1.5 NM around an offshore installation.