Which system is used in ACCs as a backup if CAATS, CSiT, or FUSION fails?

The NAV CANADA Auxiliary RADAR Display System serves as a backup primarily because it is specifically designed to provide radar display capabilities when the main systems, such as CAATS, CSiT, or FUSION, experience failures. This system ensures that air traffic controllers can continue to operate effectively by maintaining situational awareness and safe separation of aircraft, even in the event of a technical failure of the primary systems that process and display radar information.

The other systems listed do not fulfill the same role. The Extended Computer Display System primarily enhances data sharing and display capabilities but does not directly provide radar information as a backup. The Voice Switch Communications System is essential for managing communication between controllers and pilots but does not relate to radar display. The Automatic Terminal Information Service serves to provide essential information to pilots but doesn’t act as a backup radar system. Thus, the NAV CANADA Auxiliary RADAR Display System is the correct option for maintaining operational continuity in air traffic control when main systems fail.