The traffic alert and collision avoidance system (TCAS) - internationally known as the airborne collision avoidance system (ACAS) - has been mandatory on most airliners since 1993 in the US and 2000 in Europe. The system has been updated several times based on real-world experience, and looks set to get another refresh to make sure it is compatible with the US NextGen and European Sesar airspace systems.
In particular, says the FAA, TCAS needs to be modified allow use of automatic dependent surveillance - broadcast (ADS-B) and to provide collision-avoidance protection during NextGen procedures with reduced separation, such as closely spaced parallel operations. The system also needs to provide collision-avoidance protection to unmanned aircraft.
The FAA has scheduled an industry for October 11 in Washington, DC, to brief avionics manufacturers on its development plans for "ACAS X" - the next-generation TCAS II - including flight demonstrations scheduled for fiscal 2013. The FAA says its work "will be foundational to the development of minimum operational performance standards" for ACAS X by standards developer RTCA.
The FAA's plan is to leverage ADS-B technology to provide improved traffic surveillance and tracking and advanced collision-avoidance logic. Plans call for four ACAS X versions: Xa, with active surveillance and new threat logic; Xo, optimized for specific applications; Xp, with passive ADS-B reception and threat logic for surveillance; and Xu, for unmanned aircraft.
Development of ACAS X is under way with MIT Lincoln Labs, Mitre, Johns Hopkins Applied Physics Laboratory and the FAA's Atlantic City Technical Center. The International Civil Aviation organization does not expect ACAS X to be commercially available before the mid-2020s.
The latest update to TCAS/ACAS II, version 7.1, has been mandatory in Europe since March for new aircraft and will be required in all aircraft by December 2015. Version 7.1 incorporates changes resulting from the Uberlingen mid-air collision between a 757 and a Tu-154 in July 2002. Internationally, ICAO recommends version 7.1 be installed from January 2014 in new aircraft and in all aircraft by December 2017.