airborne collision avoidance system (ACAS)means an aircraft system based on secondary surveillance radar (SSR) transponder signals which operates independently of ground-based equipment to provide advice to the pilot on potential conflicting aircraft that are equipped with SSR transponders;
airborne collision avoidance system II (ACAS II)means an airborne collision avoidance system which provides vertical resolution advisories in addition to traffic advisories;
resolution advisory (RA) indicationmeans an indication given to the flight crew recommending a manoeuvre intended to provide separation from all threats or a manoeuvre restriction intended to maintain existing separation;
traffic advisory (TA) indicationmeans an indication given to the flight crew that the proximity of another aircraft is a potential threat.