Transponder Mandatory Zones (TMZ)

Transponder Mandatory Zones (TMZ) are designated volumes of airspace, often found around airports, which require aircraft to be appropriately equipped. They can be established with or without accompanying controlled airspace. TMZs are utilised to enhance the ‘visibility’ or conspicuity of aircraft operating within or in the vicinity of complex or busy airspace for the safety of all airspace operators. The airspace is established under SERA.6005* and is implemented to enhance the safe operation of flights into and out of an airport or area by providing as much information as possible to ATC without the need for excessive controlled airspace. Exceptionally, non-equipped aircraft may be permitted to enter the zones subject to compliance with pre-agreed specific criteria or Letters of Agreement.

A TMZ is annotated on a chart with a border of purple semicircles. Details of the zones can be found in the UK AIP both in the AIP General Section and, in the case of the Stansted TMZ, in the Aerodrome Section. Aircraft wishing to operate within a TMZ in the United Kingdom are required to carry and operate serviceable Secondary Surveillance Radar equipment fitted with Mode S. Aircraft wishing to operate within a TMZ without a Mode S transponder will only be accepted at the discretion of air traffic control. A TMZ may be permanent or temporary.
Learn more > Stansted TMZ