14 CFR § 135.180 - Traffic Alert and Collision Avoidance System.
(a) Unless otherwise authorized by the Administrator, after December 31, 1995, no person may operate a turbine powered airplane that has a passenger seat configuration, excluding any pilot seat, of 10 to 30 seats unless it is equipped with an approved traffic alert and collision avoidance system. If a TCAS II system is installed, it must be capable of coordinating with TCAS units that meet TSO C-119.
(1) Appropriate procedures for -
(i) The use of the equipment; and
(ii) Proper flightcrew action with respect to the equipment operation.
(2) An outline of all input sources that must be operating for the TCAS to function properly.