ACAS equipment provides two types of advisories to pilots: Resolution Advisories (RAs) and Traffic Advisories (TAs). TA is an actual warning received by the pilot, used to raise situational awareness. It gives indication to the flight crew that a certain intruder is a potential threat. RA is an indication to the pilot that a manoeuvre is necessary to provide separation from all threats or there is a need to restrict a manoeuvre and so maintain existing separation.