As a result of this and other midair collisions ( including an almost identical one in 1986 ) the " Traffic Collision Alert and Avoidance System " ( TCAS ) is now installed in all commercial passenger aircraft and in most commercial cargo airplanes . TCAS gives the pilots visual and audible warnings in the cockpit when two aircraft are approaching each other , and directs pilots to either climb or descend to avoid the other aircraft . However , the system only works if at least one aircraft is equipped with TCAS and the other with a transponder . After the 1986 Cerritos collision , all flights in Class B were required to have a Mode C transponder . The International Civil Aviation Organization does not require TCAS on the type of small , single-engined planes that were involved in the PSA disaster or the one involving AeroMexico . Only aircraft certified to carry 19 or more passengers or have a MGTOW of more than 12,600 lb are affected by the TCAS rule
an almost identical one
1986 Cerritos mid-air collision
PSA Flight 182