AC 120-55C Air Carrier TCAS - Code7700

2/23/11 AC 120-55CAppendix 6(c) For corrective RAs, the response is initiated in the proper direction within5 seconds of the RA being displayed.(d) Recognition of the initially displayed RA being modified. Response to themodified RA is properly accomplished.1. For increase rate RAs, the VS is increased within 2 1/2 seconds of the RAbeing displayed.displayed.2. For RA reversals, the VS is reversed within 2 1/2 seconds of the RA being3. For RA weakenings, the VS is modified to initiate a return towards theoriginal clearance within 2 1/2 seconds of the RA being displayed.4. For RAs which strengthen, the VS is modified to comply with the revised RAwithin 2 1/2 seconds of the RA being displayed.(e) Recognition of altitude crossing encounters and the proper response to these RAs.display.(f) For preventive RAs, the VS needle remains outside the red area on the RA(g) For maintain rate RAs, the VS is not reduced. Pilots should recognize that amaintain rate RA may result in crossing through the intruder’s altitude.(h) If a decision is made to not follow an RA, no changes in the existing VS are madein a direction opposite to the sense of the displayed RA. Pilots should be aware that if theintruder is also TCAS equipped, the decision to not follow an RA may result in a decrease inseparation at CPA because of the intruder’s RA response.(i) When the RA weakens, pilot initiates a return towards the original clearance, andwhen clear of conflict is annunciated, pilot completes the return to the original clearance.(j) Inform the controller of the RA as soon as time and workload permit, using thestandard phraseology.(k) When possible, comply with an ATC clearance while responding to an RA. Forexample, if the aircraft can level at the assigned altitude while responding to a reduce climb orreduce descent RA, it should be done.(l) If pilots simultaneously receive instructions to maneuver from ATC and an RAthat are in conflict, the pilot should follow the RA.(m)Knowledge of the TCAS multi-aircraft logic and its limitations is important. Forexample, TCAS only considers intruders that it believes to be a threat when selecting an RA. Assuch, it is possible for TCAS to issue an RA against one intruder that results in a maneuverPage 9