The Federal Aviation Administration authorizes, but does not mandate TCAS II Version 7.1 software for use in the National Airspace System (NAS). Version 7.1 is defined by FAA TSO-C119c. With introduction of TCAS II Version 7.1, the FAA now permits three versions of TCAS II in US airspace; V6.04a, V7.0 and V7.1 (note that FAA requires V7.0 or greater in RVSM airspace). More information about TCAS II can be found in the FAA’s Introduction to TCAS II V7.1 pamphlet; FAA InFO #12010, 06/26/12
On 20 December 2011, the European Commission published an Implementing Rule mandating the carriage of ACAS II version 7.1 within European Union by all aeroplanes with a maximum certified take-off mass exceeding 5,700 kg or authorised to carry more 19 passengers from 1 March 2012. An exception was made for aeroplanes with an individual certificate of airworthiness issued before 1 March 2012 that must be equipped as of 1 December 2015.
ICAO Annex 6 states that as of 1 January 2005, all turbine-engined aeroplanes of a maximum certificated take-off mass in excess of 5700 kg or authorized to carry more than 19 passengers shall be equipped with an airborne collision avoidance system (ACAS II). Amendment 85 to ICAO Annex 10 volume IV, published in October 2010, introduced a provision stating that all new ACAS installations after 1 January 2014 shall be compliant with version 7.1; and all ACAS units shall be compliant with version 7.1 after 1 January 2017.