U.S. Department of Transportation Federal Aviation Administration Advisory Circular Subject: Air Carrier Operational Approval and Use of TCAS II Date: 2/23/11 Initiated by: AFS-400 AC No: 120-55C Change:
1. PURPOSE. This advisory circular (AC) provides an acceptable, but not the only, means to address Traffic Alert and Collision Avoidance System (TCAS) issues related to installation and use of TCAS II regarding compliance with Title 14 of the Code of Federal Regulations (14 CFR) parts 121, 125, and 129 requirements for air carriers.
2. CANCELLATION. This AC cancels AC 120-55B, Air Carrier Operational Approval and Use of TCAS II, dated August 22, 2001.
3. APPLICABILITY. This AC applies to air carriers operating under part 121, other organizations conducting training approved in accordance with part 121 (for example, training centers or aircraft manufacturers), operators under part 125, and foreign air carriers conducting operations in U.S. airspace under part 129. This AC also applies to those air carriers operating under 14 CFR part 135, § 135.180, as well as any aircraft operating under 14 CFR part 91, where the operator chooses to install a TCAS II system meeting Technical Standard Order (TSO)-C119A, TSO-C119B, or TSO-C119C, TCAS II, Traffic Alert and Collision Avoidance System (TCAS) Airborne Equipment. This AC describes the TCAS operational approval process, acceptable methods for TCAS training, acceptable programs for maintenance, operational policies for TCAS use, appropriate actions in the event of a TCAS occurrence, and criteria for foreign operator use of TCAS in U.S. airspace. In addition, this AC addresses commonly asked TCAS questions in order to facilitate timely and consistent application of part 121, § 121.356, part 125, § 125.224, and part 129, § 129.18. It should be noted, however, the international standard for TCAS II, referred to as Airborne Collision Avoidance System (ACAS), includes the latest software version (v 7.0), as detailed by the International Civil Aviation Organization (ICAO).
4. RELATED 14 CFR REGULATIONS.
• Part 1, §§ 1.1 and 1.2;
• Part 71, §§ 71.9, and 71.33;
• Part 91, §§ 91.3, 91.123, 91.213, 91.215, 91.217, 91.219, 91.221, and 91.413;
• Part 119, §§ 119.7 and 119.49;
• Part 121, §§ 121.345 and 121.356;
• Part 125, §§ 125.224;
• Part 129, §§ 129.11, 129.14, and 129.18; and
• Part 135, § 135.180.
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5. DEFINITIONS. See Appendix 7. For convenience, some definitions are repeated from other pertinent FAA references. Other definitions are unique to this AC and their application is limited to use with TCAS.
6. RELATED READING MATERIAL.
a. Where You Can Find ACs (current editions). You can find ACs at http://www.faa.gov/regulations_policies/advisory_circulars. Inspectors can also access ACs through the Flight Standards Information Management System (FSIMS) at http://fsims.avs.faa.gov (see the link to http://rgl.faa.gov). Operators and the public may find this information at http://fsims.faa.gov (see the link to http://rgl.faa.gov).
(1) AC 20-131, Airworthiness and Operational Approval of Traffic Alert and Collision Avoidance Systems (TCAS II) and Mode S Transponders; and
(2) AC 20-151, Airworthiness Approval of Traffic Alert and Collision Avoidance Systems (TCAS II), Versions 7.0 & 7.1 and Associated Mode S Transponders.
b. Where to Find TSOs. You can find TSOs through FSIMS at http://fsims.avs.faa.gov (see the link to http://rgl.faa.gov).
(1) TSO-C112C, Air Traffic Control radar beacon system (ATCRBS/Mode S) Airborne Equipment; and
(2) TSO-C119A, TSO-C119B, and TSO-C119C, TCAS II Traffic Alert and Collision Avoidance System (TCAS) Airborne Equipment.
NOTE: TSO-C119A, TSO-C119B, and TSO-C119C are in effect.
c. RTCA Technical Standards Documents. These documents are available online at www.rtca.org or from RTCA Secretariat, 1828 L Street, NW, Suite 807, Washington, D.C.
20036.
(1) RTCA/DO-181D, Minimum Operational Performance Standards for ATCRBS/Mode S Airborne Equipment; and
(2) RTCA/DO-185B, Minimum Operational Performance Standards for Traffic Alert and Collision Avoidance System II (TCAS II) (for TCAS Logic Version 7.1).
7. BACKGROUND. Approval of TCAS for FAA type certificate (TC) or Supplemental Type Certification (STC) is comprehensively addressed in AC 20-131 and AC 20-151. This AC provides information for U.S. air carriers, aircraft and TCAS manufacturers, various inspectors, foreign air carriers operating in U.S. airspace, and other aviation organizations regarding standard means acceptable to the FAA to establish and ensure continued compliance with the 14 CFR as related to TCAS. This information is intended to promote timely and comprehensive program implementation, to encourage development of standard practices for the application of TCAS, and to provide for suitable followup to TCAS events.
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8. APPROVAL TO USE TCAS IN PART 121 OPERATIONS.
a. General.
(1) The use of TCAS in part 121 operations requires both FAA airworthiness certification and operational approval. Airworthiness certification of TCAS refers to an FAA approval of changes in an aircraft’s type design by amendment to a TC or issuance of an STC. Operational approval pertains to changes to training and maintenance programs, manuals, operational procedures, minimum equipment lists (MEL), and other areas necessary for safe and effective TCAS use and the qualification of aircrews through the approved training programs. An airworthiness TC/STC of a TCAS system alone does not constitute operational approval for use of TCAS under the provisions of parts 121 and 135.
(2) The following are responsibilities of various FAA offices regarding TCAS.
(a) FAA Aircraft Certification Offices (ACO) approve changes to a type design or issuance of STCs.
(b) FAA Aircraft Evaluation Groups (AEG) formulate operational criteria for specific aircraft types related to training, checking, maintenance, Master Minimum Equipment Lists (MMEL), or other operational issues, as necessary.
(c) FAA Flight Standards District Offices (FSDO) use information developed by AEG to review a particular operator’s programs. FSDOs approve a particular operator’s training and maintenance programs, operational procedures, MELs, etc., provided they are consistent with criteria specified in the MMEL, Flight Standardization Board (FSB), Maintenance Review Board (MRB) reports, and policy guidance from the Flight Standards Service (AFS), Air Transportation Division, AFS-200, and the Airworthiness Maintenance Division, AFS-300.
b. Airworthiness Approval. Criteria for TCAS airworthiness approval (TC or STC) are addressed by AC 20-131 and AC 20-151. TCAS installations are to be made in accordance with a type design change, an aircraft manufacturer’s FAA-approved Service Bulletin (SB), or by an STC.
c. Operational Approval.
(1) Approval Criteria. Operational approvals are based on criteria specified and, if applicable, training, maintenance, MMEL, or other operationally related criteria formulated by AEGs. If the criteria for training or checking are other than as specified, the criteria are available in FSB reports applicable to a particular aircraft type. The MMEL for each aircraft type specifies provisions for dispatch with inoperative equipment. Maintenance requirements are as identified in paragraph 11, except as otherwise described by an MRB report for a specific aircraft type, or in FAA-approved maintenance instructions identified in conjunction with an STC or manufacturer’s SB.
(2) Approval Methods. Accomplish TCAS operational approval through FAA approval of pertinent training programs, checklists, operations manuals, training manuals, maintenance programs, MELs, or other pertinent documents or document revisions applicable to the particular
Page 4 Par 8 air carrier. An operator’s TCAS programs are usually approved for each specific aircraft type.
However, programs common to one or more types may receive approval if TCAS program elements are common to different aircraft types, such as the same TCAS or procedures.
(3) Approval Procedures.
(a) An FAA principal inspector (PI) issues approval to use TCAS. Operators should make early contact with their respective PIs to ensure timely FAA response. Initiate such contact at the time preparations for TCAS selection or purchase, are underway and generally not later than TCAS TC/STC application.
(b) Operations specifications (OpSpecs) issuance is normally not required for U.S.
operators. The FAA reviews, accepts, and approves installations, training, maintenance programs, MELs, and other TCAS program elements in accordance with § 121.356.
9. PART 121 FLIGHTCREW QUALIFICATION FOR USE OF TCAS.
a. General.
(1) TCAS Qualification. Air carriers must ensure appropriate flightcrew TCAS qualification. The flightcrew must demonstrate proficiency in the following:
(a) Knowledge of TCAS concepts, systems, and procedures; and
(b) Cognitive, procedural, and motor skills necessary to properly respond to TCAS advisories.
(2) Acceptable Qualification Methods. First-time TCAS qualification must be accomplished for each airplane type. Qualification may be accomplished during initial, transition, or upgrade ground and flight training programs with appropriate differences. By this method, TCAS information will be integrated with other curriculum elements and modules. One may also accomplish first-time TCAS qualification as a stand-alone module of ground and flight training. Accomplish recurrent TCAS qualification during recurrent ground and flight training.
Recurrent ground training will be a stand-alone module. However, TCAS will be fully integrated with the recurrent flight training during proficiency training (PT) or Line-Oriented Flight Training (LOFT). For first-time and recurrent TCAS qualification, an instructor will accomplish evaluation of TCAS objectives during training. There are no formal TCAS evaluation requirements for flight testing or checking. Include routine TCAS operations in all evaluation environments and check airmen/examiners should include TCAS as a routine discussion item.
(3) Training Credit. Principal operations inspectors (POI) may give an operator credit when training is conducted by another operator or training center stand-alone TCAS program for first-time qualification if that program has been approved by the FAA and if aircraft, TCAS system, procedures, and other relevant factors or circumstances are the same or equivalent to those of the operator seeking credit. The POI should consult with the appropriate division of AFS, National Simulator Evaluation Team (NSET), or the assigned AEG about the suitability of a proposed program for a particular version of TCAS or aircraft type.
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b. TCAS Training Program Requirements.
(1) Curriculum. Appendix 6 contains the required areas of instruction for ground training for the first-time TCAS qualification. For subsequent type airplanes and for recurrent training, only the new, revised, or emphasized items need to be addressed. Appendix 6 also contains the objectives and related simulation characteristics required for flight training.
(2) Evaluation of TCAS Knowledge and Skills (Maneuvers).
(a) Evaluate TCAS knowledge with written, oral, or computer-based instructional tests. Combinations of these methods may be used if the required body of knowledge is completely covered. For any of these methods, one must achieve a passing grade of 90 percent.
First-time qualification in any type airplane must include evaluation of all knowledge areas. For recurrent training, complete coverage of the knowledge requirements must be completed every 36 months.
(b) An instructor must evaluate TCAS skills (maneuvers) for first-time TCAS qualification in each type airplane. This evaluation may be accomplished by an instructor in a qualified flight training device (FTD), simulator, or computer-based instruction (CBI) approved for each maneuver. For recurrent training, maneuver training must include response to all types of RAs during any 36-month training period. Recurrent training is desirable in an FTD or simulator approved for the maneuvers.
(3) LOFT. LOFT programs using simulators equipped with TCAS should be enhanced by an interactive TCAS. In addition, LOFT programs should consider proper crew vigilance for aircraft that may not be transponder or Mode C equipped. Advisories accomplished during LOFT are creditable toward first-time or recurrent qualification.
c. Training Center Approval. Training centers conducting training, such as contract training or aircraft manufacturers may have TCAS elements of those programs approved if curriculum requirements (ground and flight) provided in Appendix 6 are met.
d. Initial Evaluation of TCAS Knowledge and Skills. Evaluate individual crewmember TCAS knowledge and skills prior to TCAS use. Acceptable means of initial assessment include the evaluation by an authorized instructor or check airman using written, computer-based, or oral tests, and a simulator, FTD, or CBI system capable of depicting traffic encounters.
e. TCAS Recurrent Training. Integrate TCAS recurrent training into other established recurrent training programs. Recurrent training for TCAS must include both ground and flight (maneuver) and should address any significant issues identified by line Operating Experience (OE), system changes, procedural changes, or unique characteristics such as the introduction of new aircraft/display systems or operations in airspace where high numbers of traffic advisories (TA) and Resolution Advisories (RA) have been reported.
f. TCAS Recurrent Evaluation. Incorporate recurrent TCAS as an element of routine proficiency training.
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g. Line Checks and Route Checks. When using TCAS-equipped aircraft during line or route checks, check airmen should routinely incorporate proper TCAS use as a discussion item.
h. LOFT. LOFT programs using simulators equipped with TCAS should be enhanced by interaction with the TCAS. In addition, LOFT programs should consider proper crew vigilance for aircraft which may not be transponder or Mode C equipped.
i. Crew Resource Management (CRM). CRM programs should address effective teamwork in responding to TCAS events with emphasis on the following areas:
(1) The crew should conduct preflight briefings on how to handle TCAS advisories; and
(2) The proper reaction to a TA by the Pilot Flying (PF) and the pilot monitoring (PM).
10. OTHER OPERATIONAL ISSUES.
a. Manuals and Other Publications. Airplane flight manuals, operating manuals, maintenance manuals, general policy manuals, other manuals, publications, or written material (such as operating bulletins that may relate to TCAS use) must be appropriately amended to describe TCAS equipment, procedures, and operational policies according to the appropriate regulation.
b. MMEL/MEL.
(1) Operators formulate necessary TCAS revisions to their MELs for each particular fleet (for example, B727, DC10). MEL revisions must be consistent with the FAA MMEL established for each aircraft type. A summary of the process for addressing the necessary changes to MEL items as well as examples of MMEL and acceptable MEL provisions for TCAS are in Appendix 3.
(2) The MMEL changed April 6, 2000, and the relief category changed from C to B for the entire system.
c. Aircraft with TCAS Differences. Operators who have aircraft with TCAS differences in displays, controls, procedures, or involved with interchange operations must account for those TCAS differences. Accomplish this as part of an approved differences training program in accordance with § 121.418, or as otherwise specified in applicable FAA FSB reports concerning crew qualification pertaining to a particular airplane type.
d. Issues Unique to a Particular Operator. Operators should address any TCAS issues that may be unique to their particular route environment, aircraft, procedures, or TCAS display and control features. Examples include the following:
(1) Route Environment Issue. Air carriers having takeoffs or landings outside of the reference TCAS performance envelope (for example, airport elevations outside of the range between sea level and 5,300 feet mean sea level (MSL), or temperatures outside the range of International Standard Atmosphere (ISA) (±50° F) should advise crews of appropriate procedures and precautions regarding RA compliance. To ensure proper response to the TCAS in
Par 10 Page 7 limiting performance conditions (for example, TCAS RA during takeoff climb or in final landing configuration at high altitude airports such as Mexico City and La Paz), specific procedures or training may be necessary, unless a bulletin or manual information can adequately address these situations.
(2) A Procedural Issue. Air carriers should describe the use of TA-only mode of operation when required on certain aircraft with an engine failure.
(3) A Unique TCAS Issue. Do not use TCAS flight level or absolute display of traffic altitude on a traffic display during operations when the altimeter is set to reference zero feet at field elevation (QFE).
e. Response to TCAS RA for Aircraft at Maximum Certified Altitude.
(1) Aircraft not inhibited to climb when at maximum certified altitude should climb in response to TCAS climb RAs.
(2) Aircraft that are climb inhibited from TCAS climbs at maximum certified altitude will be issued a “DO NOT DESCEND” RA.
11. MAINTENANCE.
a. General. Maintenance procedures for TCAS receive approval or acceptance as part of an operator’s initial maintenance manual approval or as a revision to that manual. TCAS maintenance procedures should be consistent with the TCAS manufacturer’s maintenance procedures and/or aircraft manufacturer’s maintenance procedures for TCAS.
b. Maintenance Training. An operator must provide adequate TCAS maintenance training in accordance with the appropriate regulation to ensure that its maintenance personnel or contract maintenance personnel are able to properly implement TCAS-related maintenance programs.
This includes, but is not limited to, addressing installation, modification, correction of reported system discrepancies, and use of test equipment, procedures, MEL relief, and return-to-service authorizations. The training procedures should address testing installed transponders and automatic pressure altitude reporting equipment on the ground in such a way that false targets are not generated in airborne TCAS systems. A method for eliminating potential interference with TCAS-equipped aircraft during transponder testing would be the use of shields for the transponder antennas. ACs 20-131 and 20-151 provide more detailed information and guidance concerning the proper procedures to follow when conducting operational testing of TCAS II or transponders on the ground.
c. TCAS Software Updates. When necessary, operators should ensure that appropriate TCAS software updates are incorporated. The latest version of software for TCAS II is version 7.1. To ensure compatibility with international standards, the FAA encourages the installation of this software as soon as practical. Software version 6.04A, version 7.0, and version 7.1 are all approved for operations in U.S. airspace.
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12. TCAS OPERATIONAL USE.
a. General. Operationally, those skills addressed and the guidance provided on TCAS training in paragraph 9 should be followed and implemented by each operator electing to use TCAS II.
NOTE: In no case should a pilot maneuver opposite to a TCAS RA.
b. Pilot Responsibilities. A TCAS is intended to serve as a backup to visual collision avoidance, application of right-of-way rules, and air traffic separation service. For TCAS to work as designed, immediate and correct crew response to TCAS advisories is essential. Delayed crew response or reluctance of a flightcrew to adjust the aircraft’s flightpath as advised by TCAS due to air traffic control (ATC) clearance provisions, fear of later FAA scrutiny, or other factors could significantly decrease or negate the protection afforded by TCAS. Flightcrews should respond to a TCAS in accordance with the following guidelines when responding to alerts:
(1) Respond to TAs by attempting to establish visual contact with the intruder aircraft and other aircraft which may be in the vicinity. Coordinate to the degree possible with other crewmembers to assist in searching for traffic. Do not deviate from an assigned clearance based only on TA information. For any traffic acquired visually, continue to maintain safe separation in accordance with current regulations and good operating practices.
(2) When an RA occurs, the PF should respond immediately by direct attention to RA displays and maneuver as indicated, unless doing so would jeopardize the safe operation of the flight or the flightcrew can assure separation with the help of definitive visual acquisition of the aircraft causing the RA. By not responding to an RA, the flightcrew effectively takes responsibility for achieving safe separation. In so choosing, consider the following cautions:
(a) The traffic may also be equipped with TCAS and it may maneuver in response to an RA coordinated with your own TCAS.
(b) The traffic acquired visually may not be the same traffic causing the RA.
(c) Visual perception of the encounter may be misleading. Unless it is unequivocally clear that the target acquired visually is the one generating the RA and there are no complicating circumstances, the pilot’s instinctive reaction should always be to respond to RAs in the direction and to the degree displayed.
(3) Satisfy RAs by disconnecting the autopilot (if necessary) and auto throttle system, (when required by the airframe manufacturer’s procedures), and using prompt positive control inputs in the direction and with the magnitude the TCAS advises. To achieve the required vertical rate (normally 1,500 feet per minute (fpm) climb or descent), first adjust the aircraft’s pitch using the suggested guidelines shown in the table below. Then refer to the vertical speed indicator (VSI) and make all necessary pitch adjustments to place the VSI in the green arc.
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SPEED PITCH ADJUSTMENT .80 MACH 2° 250 knots indicated airspeed (KIAS) below 10,000 feet 4° APPROACH below 200 KIAS 5° to 7°
(a) On aircraft with pitch guidance for TCAS RA displays, follow the RA pitch command for initial, increase, reversal, and weakening RAs.
(b) For the TCAS to provide safe vertical separation, initial Vertical Speed (VS) response is required within 5 seconds of when the RA is first displayed. Excursions from assigned altitude, when responding to an RA, typically should be no more than 300 to 500 feet to satisfy the conflict. VS responses should be made to avoid red arcs or outlined pitch avoidance areas and, if applicable, to accurately fly to the green arc or outlined pitch guidance area.
(4) Respond immediately to any increase or reversal RA maneuver advisories. Initial VS response to an increase or reversal RA is expected by the TCAS within 2 1/2 seconds after issuance of the advisory. Again, avoid red arcs or outlined pitch avoidance areas and fly to the green arc or outlined pitch guidance area.
(5) The PM should advise the PF on the progress of achieving the vertical rates commanded by the TCAS. The PM and any onboard observers will assist in the visual search for the intruder and continue to cross-check the TCAS displayed information with other available traffic information to ensure the RA response is being flown correctly.
(6) If an initial corrective RA is downgraded or weakened, such as a “climb” RA downgraded to a “do not descend” RA, pilots should respond to the weakening RA and adjust the aircraft’s VS to the rate depicted by the green (fly to) arc or line on the instantaneous VS indicator (IVSI) or other suitable indicator, while keeping the needle or pitch guidance symbol out of the red arc or outlined pitch avoidance area. Pilots should remember that attention to the RA display and prompt reaction to the weakened RA will minimize altitude excursions and potential disruptions to ATC. This will allow for proper resolution of encounters and reduce the probability of additional RAs against the intruder or other traffic.
(7) Evasive maneuvering must be limited to the minimum required to comply with the RA. Excessive responses to RAs are not desirable or appropriate because of other potential traffic and ATC consequences. From level flight, proper response to an RA typically results in an overall altitude deviation of 300 to 500 feet in order to successfully resolve a traffic conflict.
(8) In some instances it may not be possible to respond to a TCAS RA and continue to satisfy a clearance at the same time. Even if a TCAS RA maneuver is inconsistent with the current clearance, respond appropriately to the RA. Since TCAS tracks all transponder-equipped aircraft in the vicinity, responding to an RA for an intruder assures a safe avoidance maneuver from that intruder and from other Mode C equipped aircraft. Guidance in this paragraph does not conflict with that in paragraph 12b(2).
(9) If a TCAS RA requires maneuvering contrary to right of way rules, cloud clearance rules for visual flight rules (VFR), instrument flight rules (IFR), or other such criteria, pilots
Page 10 Par 12 should follow the TCAS RAs to resolve the immediate traffic conflict. Deviations from rules or clearances should be kept to the minimum necessary to satisfy a TCAS RA.
(10) If a TCAS RA response requires deviation from an ATC clearance, expeditiously return to the current ATC clearance when the traffic conflict is resolved, the TCAS “clear of conflict” message is heard, or follow any subsequent change to clearance as advised by ATC. In responding to a TCAS RA that directs a deviation from assigned altitude, communicate with ATC as soon as practicable after responding to the RA. When the RA is cleared, the flightcrew should advise ATC that they are returning to their previously assigned clearance or should acknowledge any amended clearance issued. In addition, the flightcrew’s discretionary use of other types of reports may be desired. See Appendix 5 for suggested phraseology.
(11) If a TCAS RA maneuver is contrary to other critical cockpit warnings, then those other critical warnings are respected as defined by TCAS certification and training (that is, responses to stall warning, windshear, and ground proximity warning system (GPWS) take precedence over a TCAS RA, particularly when the aircraft is less than 2,500 feet above ground level (AGL)).
(12) Pilots should use TCAS traffic information displays to increase their awareness of nearby traffic and to assist in establishing visual contact with other aircraft. Certain electronic flight information system (EFIS) TCAS installations operating in conjunction with “track up” mode may require the pilot to make allowances for the difference between the aircraft heading and track when visually sighting nearby aircraft.
(13) Unless approved by the Administrator, pilots should operate TCAS while in-flight in all airspace, including oceanic, international, and foreign airspace.
(14) When feasible, flightcrews should use the same altitude data source used by the PF to provide altitude information to TCAS and the ATC transponders. Using a common altitude source precludes unnecessary RAs due to differences between altitude data sources.
(15) Note and accurately report TCAS encounters and system anomalies in accordance with operator policies so that remedial improvements to TCAS or the National Airspace System (NAS) can be made.
NOTE: ARINC operates a Web-based data collection scheme on behalf of the FAA. The Web site can be found at www.tcasreport.com.
(16) The TCAS does not alter or diminish the pilot’s basic authority and responsibility to ensure safe flight. Since the TCAS does not respond to aircraft which are not transponder equipped or aircraft with a transponder failure, a TCAS alone does not ensure safe separation in every case. TCAS RAs may, in some cases, conflict with flight path requirements due to terrain, such as an obstacle-limited climb segment or an approach to rising terrain. Since the basis for many approved instrument procedures and IFR clearances is avoiding high terrain or obstacles, it is particularly important that pilots maintain situational awareness (SA) and continue to use good operating practices and judgment when following TCAS RAs. Pilots should make frequent outside visual scans while using see-and-avoid techniques. Communication with ATC should be initiated as necessary.
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c. Consequences of Disregarding RA Information. The potential consequences of disregarding RA information include:
(1) An aircraft seen visually may not necessarily be the aircraft causing the RA or may not be the only aircraft to which TCAS is responding.
(2) It is difficult to visually determine the vertical displacement of other aircraft especially when ground reference information is unreliable or at cruise altitudes where the earth’s horizon is obscured. Therefore, disregarding RA information and maneuvering vertically based solely on visual acquisition may result in a loss of safe separation.
(3) ATC may not know when TCAS issues RAs. It is possible for ATC to unknowingly issue instructions that are contrary to the TCAS RA indications. Safe vertical separation may be lost during TCAS coordination when one aircraft maneuvers opposite the vertical direction indicated by TCAS and the other aircraft maneuvers as indicated by TCAS. As a result, both aircraft may experience excessive altitude excursions in vertical chase scenarios due to the aircraft maneuvering in the same vertical direction. Accordingly, during an RA, do not maneuver contrary to the RA based solely upon ATC instructions.
(4) ATC may not be providing separation service or be communicating with the aircraft causing the RA.
(5) Disregarding RA during a coordinated encounter with another TCAS-equipped aircraft can result in loss of safe separation.
d. TCAS Good Operating Practices. The following are identified TCAS good operating practices:
(1) To preclude unnecessary transponder interrogations and possible interference with ground radar surveillance systems, do not activate TCAS (TA-only or TA/RA mode) until taking the active runway for departure. A transponder selected to “XPDR” or “ON” is adequate for ATC and nearby Automatic Dependent Surveillance-Broadcast (ADS-B)-equipped aircraft to “see” the aircraft while taxiing on the airport surface.
(2) Following landing and clearing of the runway, de-select TCAS from TA or TA/RA mode. Select “XPNDR” or “ON” while taxiing to the ramp area. Upon shutdown, select “STBY” on the transponder.
(3) During flight, use TCAS displays to enhance SA. Use displays which have a range selection capability in an appropriate range setting for the phase of flight. For example, use minimum range settings in the terminal and longer ranges for climb/descent and cruise as appropriate.
(4) Note that TCAS RAs can be generated while aircraft are legally separated.
(5) It is appropriate to operate TCAS in the TA-only mode in circumstances where unnecessary RAs frequently occur and where such RAs are disruptive to the operation of the aircraft. These circumstances may include:
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(a) During takeoff towards known nearby traffic that is in visual contact and which could cause an unwanted RA during initial climb, such as a visually identified helicopter passing near the departure end of the runway. Select the TA/RA mode after the potential for an unwanted RA ceases to exist, such as after climbing above a known VFR corridor.
(b) In instrument or visual conditions during approaches to closely spaced parallel runways.
(c) In visual conditions, when flying in close proximity to other aircraft.
(d) At certain airports, during particular procedures, or in circumstances identified by the operator as having a significant potential for unwanted or inappropriate RAs.
(e) In the event of particular in-flight failures, such as engine failure, as specified by the Aircraft Flight Manual (AFM) or operator.
(f) During takeoffs or landings outside of the nominal TCAS reference performance envelope for RAs, as designated by the AFM or operator. TCAS reference performance for RAs is typically attainable during takeoffs and landings at airports within the envelope of ISA ±50°F, sea level to 5,300 feet MSL. When takeoffs or landings are outside of this envelope, use of a TA only may be appropriate during the limited time period when TCAS reference performance cannot be achieved. This typically occurs when the aircraft is at low speed in specified limiting configurations during takeoff or landing at hot day high altitude airports, such as Mexico City or La Paz.
(6) When safe, practical, and in accordance with the air carrier’s approved operating procedures, pilots should limit VS to 1,500 fpm or less when within 2,000 feet of assigned altitudes. This procedure will reduce the frequency of unnecessary RAs and be in conformance with the Aeronautical Information Manual (AIM) and ICAO guidance.
e. Operator Responsibilities. Operators have the following general responsibilities regarding TCAS:
(1) Assure followup and evaluation of unusual TCAS events; and
(2) Periodically assess TCAS training, checking, and maintenance programs to ensure their correctness, pertinence, timeliness, and effectiveness.
f. ATC Responsibilities. Highlighted below are ATC responsibilities relating to TCAS.
(1) Controllers will not knowingly issue instructions that are contrary to RA guidance when they are aware that a TCAS maneuver is in progress. When an aircraft deviates from its clearance in response to an RA, ATC is still responsible for providing assistance to the deviating aircraft as requested until:
(a) The pilot informs ATC that the RA conflict is clear; and the aircraft has returned to the previously assigned altitude; or