This are the requirements for JAR-OPS 1 aircraft.
Quote:
JAR-OPS 1.668 Airborne Collision Avoidance System
(See IEM OPS 1.668)
(a) An operator shall not operate a turbine powered aeroplane:
(1) Having a maximum certificated takeoff mass in excess of 15 000 kg or a maximum approved passenger seating configuration of more than 30 after 1 January 2000; or
(2) Having a maximum certificated takeoff mass in excess of 5 700 kg, but not more than 15 000 kg, or a maximum approved passenger seating configuration of more than 19, but not more than 30, after 1 January 2005,
unless it is equipped with an airborne collision avoidance system with a minimum performance level of at least ACAS II.
Unquote: