Currently, Traffic Alert and Collision Aviodance System(s) (TCAS) are required in the United States on all commercial aircraft with more than 10 seats. TCAS I is required on aircraft with 10-30 seats although TCAS II can be installed instead. TCAS II is required in aircraft with more than 30 seats but may be installed in smaller planes. Some other countries are requiring the installation of Airborne Collision Avoidance Systems (ACAS) on larger aircraft.