Advisory US. Department of Transportation Circular Federal Anarion Administration Subject: AIR CARRIER OPERATIONAL Dale: 8/27/93 AC No: 120-55A APPROVAL AND USE OF TCAS II Initiated by: AFS-450 Change:
PURPOSE. This Advisory Circular (AC) provides an acceptable means, 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 Federal Aviation Regulations (FAR) Parts 121, 125, and 129 requirements for air carriers.
2. CANCELLATION. Advisory Circular 120-55, dated October 23, 1991, is hereby canceled.
3. APPLICABILITY. This AC applies to air carriers operating under FAR Part 121, other organizations conducting training approved in accordance with FAR Part 121 (e.g., training centers or aircraft manufacturers), operators under FAR Part 125, and foreign air carriers conducting operations in U.S. airspace under FAR Part 129.
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 FAR SS 121.356, 125.224, and 129.18. While not specifically addressing FAR Part 135 operations, the principles described by this AC may also be applied to those air carriers operating under FAR Part 135 who choose to install TCAS II, as well as any aircraft operating under FAR Part 91.
4. RELATED MATERIAL.
a • FAR SS 1.1, 1.2, 91.3, 91.123, 91.213, 91.215, 91.217,
91.219, 91.221, 91.413, 121.345, 121.356, 125.224, 129.11, and
129.18.
Advisory Circular 20-131, Airworthiness and Operational Approval of Traffic Alert and Collision Avoidance Systems (TCAS II) and Mode S Transponders, current edition.
Federal Aviation Administration (FAA) /Technical Standard Order (TSO) C112, Air Traffic Control Radar Beacon System (ATCRBS) /Mode S, and ISO-C119A, TCAS II Airborne Equipment.
Copies may be obtained from the Department of Transportation, FAA, Aircraft Certification Service, Aircraft Engineering Division, AIR-120, 800 Independence Avenue, SW., Washington, D.C. 20591.
a. Radio Technical Commission for Aeronautics (RTCA), Document No. RTCA/DO-185, Minimum Operational Performance Standards for TCAS II Airborne Equipment, Volume II, Consolidated Edition. Copies may be purchased from the RICA Secretariat, 1140 Connecticut Avenue, NW., Suite 1020, Washington, D.C. 20036.
5. HOW TO ORDER.
a. Copies of this AC and others mentioned herein may be obtained from:
Department of Transportation General Services Section M-443.2 Washington, DC 20590
b. Identify this publication in your order as:
FAA Advisory Circular 120-55A Air Carrier Operational Approval and Use of TCAS II
6. BACKGROUND AND DEFINITIONS.
a. TCAS Implementation. TCAS systems are now implemented in FAR Part 121 operations and other applications. Approval of TCAS for FAA Type Certification (IC) or Supplemental Type Certification (STC) is comprehensively addressed in AC 20-131, as amended. 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 FAR related to TCAS. This information is intended to facilitate TCAS system design and certification, promote timely and comprehensive program implementation, encourage development of standard practices for application of TCAS, and provide for suitable followup to TCAS events.
are are to this e in tor ane, a co For convenience, some definitions in this AC are repeated from other pertinent FAA references. Other definitions are unique to this AC and their application is limited to use with
(1) Aircraft Certification Office (ACO). FAA offices responsible for determination of aircraft airworthiness regarding issuance of TC's, STC's, and other issues related to FAR Parts 21, 23,25, 33, and other similar airworthiness rules. ACO's are als‹ responsible for technical assessment of service difficulties including issuance of Airworthiness Directives.
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(2) Aircraft Evaluation Group (AFG). FAA offices responsible for operational aspects of newly certificated, modified, or "in service" aircraft. AEG's establish FAA criteria for pilot qualification, minimum equipment lists (MEL), initial airworthiness, and other such requirements as they relate to FAR Parts 43, 61, 91, 121, 135, and other operationally related FAR.
(3) Altitude Limit (ALIM). ALIM is the specified amount of vertical separation that TCAS is designed to provide between aircraft. It is also the altitude threshold for the issuance of a corrective resolution advisory (RA). The value of ALIM varies with
(4) Altitude Threshold (ZTHR). The altitude threshold for the issuance of a preventive RA. The ZTHR varies with aircraft altitude.
(5) Certificate Holding District Office (CHDO). A Flight Standards office that is responsible for administration of a FAR Part 121 and FAR Part 135 operating certificate for a particular operator.
(6) Coordination (as related to TCAS). The process by which TCAS units in conflicting aircraft communicate with one another to select complementary resolution advisories to resolve an encounter
(i.e., one unit selects a Climb, the other a Descend).
(7) Flight Standards District Office (FSDO). An FAA field office serving an assigned geographical area and staffed with Flight Standards personnel who serve the aviation industry and the general But on are cosion public on matters relating to the certification and operation of air carrier and general aviation aircraft.
(8) Flight Standardization Board (FSB). The FAA board responsible for establishing or revising crew qualification requirements (e.g., training, checking, currency, and type rating(s)) for specific aircraft. FSB's are established for each large turbojet, turboprop, and Special FAR Part 41 airplane type used in air transportation, as well as other FAR Part 25 airplanes, transport category multiengine helicopters, and large multiengine piston airplanes.
(9) Follow-on STC (As related to TCAS). A TCAS STC other than as described in item 6b(10) for an "Initial TC/STC." The following examples are considered to be "follow-on" ST's:
(i) A previously approved TCAS II installation which is installed in a subsequent type or model aircraft.
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(ii) Changes of display configuration (weather radar/TCAS display), supporting system (Radar Altimeter) or other aircrait interface (1.e., ground proximity warning system (GPS), etc.).
(10) Initial TC/STC (As related to TCAS). The first FAA TCAS airworthiness approval (in accordance with a TC or STC) of any one or combination of the following components: A TCAS processor (computer), TCAS directional antenna, and/or Mode s transponder.
(NOTE: For previously approved TCAS systems, if the part number of any of the above components changes due to a significant modification, the system change requires an initial TC/STC).
(11) Intruder. A target which has satisfied the traffic advisory detection criteria.
(12) Limited Implementation Program (LIP). A TCAS evaluation program conducted by selected U.S. operators in conjunction with FAA prior to finalization of regulatory requirements for TCAS.
(13) Master Minimum Equipment List (MMEL). An FAA document listing stipulations in accordance with FAR § 121.627 (c) and FAR § 135.179 that provides authorization for the continuation of flight beyond a terminal point with certain equipment inoperative.
AEG's develop MMEL's in conjunction with a Flight Operation Evaluation Board (FOEB) established for each aircraft type. FAA MMEL's serve as the basis for an operator to develop specific MEL's applicable to its particular aircraft and operational requirements.
(14) Maintenance Review Board (MRB). An FAA board responsible for establishing maintenance requirements for a specific aircraft type. MRB requirements are usually formulated in conjunction with information provided by the manufacturer and prospective operators through industry working groups. FAA CHDO's apply MRB requirements in reviewing and approving each carrier's proposed maintenance program.
(15) National Airspace System (NAS). The common network of U.s. airspace; air navigation facilities, equipment and services, airports or landing areas; aeronautical charts, information and services; rules, regulations, and procedures; technical information, manpower, and material; and system components shared jointly with the military.
(16) National Simulator Evaluation Team (NSET). Team of FAA operations specialists responsible for evaluating flight simulators to aid principal operations inspectors (POI) in approving those simulators in accordance with FAR requirements (e.g., NSET Par 6 4
evaluations support POI approval of a particular simulator for use in a specific FAR Part 121 program).
(17) Other Traffic. An intruder aircraft which is within the selected display range that is not proximate traffic and does not meet the threat criteria of a traffic advisory or resolution advisory.
(18) Principal Inspector (PI). Refers to one of three FAA principal inspectors: principal avionics inspector, principal operations inspector, or principal maintenance inspector.
(19) Principal Avionics Inspector (PAI). The FAA inspector assigned responsibility for overseeing all avionics issues relative to a specific operator, to include input to training programs, operations specifications, MEL requests, etc.
(20) Principal Operations Inspector (POI). The FAA inspector assigned responsibility for overseeing all operational issues elative to a specific operator, including training programs perations specifications approval, MEL approval requests, etc.
(21) Principal Maintenance Inspector (PMI). The FAA inspector assigned responsibility for overseeing all maintenance issues relative to a specific operator, to include input to training programs, operations specifications, MEL requests, etc.
(22) Proximate Traffic. An intruder aircraft which is within 6 nautical miles (nm) in range and within plus or minus 1,200 feet vertically, but does not meet the threat criteria of a traffic advisory or resolution advisory.
(23) Resolution Advisory (RA). Aural voice and display information provided by TCAS to a flightcrew, advising that a particular maneuver should, or should not, be performed to maintain safe separation from a threat aircraft.
(i) Corrective RA. A corrective RA is an advisory issued by TCAS that requires a pilot to modify the aircraft's existing vertical speed.
(11) Crossing RA. An RA that directs a pilot to cross through the intruder aircraft's altitude in order to achieve safe vertical separation.
(iii) Increase RA. An RA that is issued after an initial Climb or Descend RA which indicates additional climb or descent rate is required to achieve safe vertical separation. An Par 6
increase rate RA requires a climb or descent rate of 2,500 feet per minute (fpm).
(iv) Preventive RA. A preventive RA is an advisory issued by TCAS that requires a pilot to maintain an existing vertical speed or avoid certain vertical speeds.
(v) Reversal RA. A reversal RA indicates a reverse in direction is required to achieve safe vertical separation (i.e., an initial descend RA reverses to a climb RA).
(vi) Weakened RA. An initial corrective RA that changes to an RA requiring less vertical speed because TCAS has determined that safe vertical separation is projected (i.e., a climb RA that softens to a do not descend advisory.
(24) Significant TCAS Events. Significant TCAS events are those which meet any one of the following guidelines:
(i) There is a loss of standard air traffic control (ATC) separation resulting from compliance with a TCAS- generated RA.
(ii) TCAS is suspected as not performing as desired.
(iii) A crewmember's use of the TCAS system appears to be improper.
(iv) There is an altitude excursion of more than 1,500 feet from an assigned level altitude.
(25) Tau. Greek symbol representing the time to closest point of approach.
(26) Threat. An intruder which has satisfied the threat detection criteria and thus requires an RA.
(27) Traffic. Intruder aircraft with an operating transponder capable of being tracked by a TCAS-equipped aircraft.
(28) Traffic Advisory (TA). Aural and display information provided by ICAS to a flightcrew, identifying the location of nearby traffic meeting certain minimum separation criteria.
(29) ICAS. Traffic Alert and Collision Avoidance System. A family of airborne devices meeting specified TSO and RICA/DO-185 requirements, as amended, which function independently of the groundbased ATC system to provide collision avoidance information.
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(1) TCAS 1. A Traffic Alert and Collision Avoidance System providing only TA's to assist pilots in the visual acquisition of intruder traffic.
(ii) TCAS II. A Traffic Alert and Collision Avoidance System which provides TA's and RA's in the vertical plane (e.g., climb or descend).
(iii) TCAS III. A Traffic Alert and Collision Avoidance System providing TA's and RA's in both the horizontal and the vertical planes to avoid conflicting traffic.
(30) ICAS Academic Training (As applied within this AC).
Training which exclusively addresses knowledge requirements (rather than skills), and is usually related to achieving satisfactory knowledge of TCAS concepts, systems, limitations, or procedures.
TCAS academic training generally is accomplished using a combination of classroom methods (standup instruction, slide/tapes, computerbased instruction, tutorial, etc.), flight manual information, bulletins, or self-study. See paragraph 8b for an expanded explanation of what should be taught.
(31) TCAS Event. For the purpose of this AC, one or more of the following occurrences or situations related to TCAS:
Issuance of any TCAS RA or TA as specified by a flightcrew (regardless of whether it is valid, unwanted, or nuisance),
(ii) Other TCAS-related in-flight traffic conflicts or potential conflicts as determined by a flightcrew,
(iii) Near mid-air collisions (NMAC) involving a TCAS- equipped aircraft,
(iv) TCAS system failures related to a traffic conflict, potential traffic conflict situation, or TCAS general system performance,
(v) ATC system error involving a TCAS-equipped aircraft, or Other TCAS occurrences or situations related to potential TCAS or ATC system safety performance.
(32) TCAS Maneuver Training (As applied within this AC).
Training which addresses both knowledge and skills and is usually related to achieving satisfactory performance of a particular TCAS procedure or maneuver, or series of procedures or maneuvers.
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(33) TCAS Transition Program (TTP). A phased TCAS implementation and evaluation program established to assure timely and effective TCAS installation and use for U.S. air carrier aircraft and to assist in the integration of a large number of TCAS units in the NAS.
(34) Type Certificate (TC). An FAA certificate attesting to the fact that the respective aircraft, engines, or other components meet airworthiness requirements of the FAR.
(35) Supplemental Type Certificate (STC). An FAA certificate attesting to the fact that modifications to the respective aircraft, engines, or other components meet airworthiness requirements of the
7. APPROVAL TO USE TCAS IN FAR PART 121 OPERATIONS.
a. General.
(1) Use of TCAS in FAR 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, MEL's, and other such areas necessary for safe and effective TCAS use. An airworthiness TC/STC of a TCAS system alone does not constitute operational approval for use of TCAS under provisions of FAR Part 121.
(2) Responsibilities of Various FAA Offices Regarding TCAS.
FAA ACO's approve changes to a type design or issuance of STC's.
AEG's formulate operational criteria for specific aircraft types celated to training, checking, maintenance, MMEL s or other operatlonal issues, as necessary. FAA FSDO's use informatior developed by AEG's to review a particular operator's programs.
FSDO's approve a particular operator's training and maintenance programs, operational procedures, MEL's, etc., if they are consistent
b. Airworthiness Approval.
Criteria for TCAS airworthiness approval (TC or SIC) are addressed by AC 20-131, as revised. TCAS installations are to be an aircraft Par 6
c. Operational Approval.
(1) Approval Criteria. Operational approvals are based on criteria in this AC and, lated licable, traininte maintenance, MEL, or other operationally related criteria formulated by AEG's.
criteria for training or checking are other than as specified in this AC, the criteria may be found in FSB reports applicable to a particular aircraft type. Provisions for dispatch with inoperative equipment are specified by the MMEL for each aircraft type.
Maintenance requirements are as identified by this AC, except as otherwise described by a MRB report for a specific aircraft type, or in FAA-approved maintenance instructions identified in conjunction with an STC or manufacturer's Service Bulletin.
Approval Methods. TCAS operational approval is accomplished through FAA approval of pertinent training programs, checklists, operations manuals, training manuals, maintenance programs, MEL's, or other pertinent documents or document revisions applicable to the particular air carrier. Operators' TCAS programs are usually approved for each specific aircraft type. However, programs common to one or more types may be approved if TCAS program elements are common to different aircraft types (e.g., same TCAS systems, procedures, etc.).
(3) Approval Procedures.
(1) Approval to use TCAS is issued by an FAA PI.* Operators should make early contact with their respective PI's to permit timely FAA response. Usually such contact is initiated at the time preparations are being made for TCAS system selection or purchase, and generally not later than TCAS TC/STC application.
*NOTE: Each operator is assigned three FAA PI's as follows: A POI, a PMI, and a PAI. PI's are usually located in the CHDO.
Operations specifications normally are not required for U.S. operators. Installations, training, maintenance programs, MEL's, and other TCAS program elements are reviewed and accepted or approved by the FAA. TCAS operations specifications regarding FAR § 121.356 are not necessary. However, in the event of TCAS service difficulties, or in other special instances, the FAA may require certain operations specifications provisions.
8. FAR PART 121 FLIGHTCREW QUALIFICATION FOR USE OF TCAS.
a. General.
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(1) TCAS Qualification Issues and Objectives. Air carriers should address the following issues and objectives to assure appropriate flightcrew TCAS qualification:
(1) Address necessary flightcrew knowledge of TCAS concepts, systems, and procedures (ICAS Academic Training).
Develop necessary flightcrew skills to properly respond to TCAS advisories (TCAS Maneuver Training).
(iii) Assess each pilot's ability to properly use TCAS (TCAS Initial Evaluation).
(iv) Maintain appropriate TCAS knowledge and skills (TCAS Recurrent Qualification).
(2) Acceptable Qualification Means. First time TCAS training and qualification should be addressed during initial, the grated veth che curiou seen be carple, frately br qualification may be keyed to specific aircraft during transition, upgrade, or differences courses (e.g., during DC-10 transition), may be addressed in conjunction with general training (e.g.. during initial "new hire" indoctrination), or may be addressed conjunction with recurrent training or checking events (e.g., in conjunction with recurrent proficiency check or proficiency training (PC/PT), or line-oriented flight training (LOFT)). TCAS qualification may also be addressed as a separate program (e.g., by completion of a standardized TCAS curriculum at an operator's training center, or at designated crew bases).
(3) Credit for Use of Other Programs. Each operator intending to receive credit for TCAS training when the program being proposed is based on LIP experience, or when the training is to be conducted by another operator, training center, or manufacturer, must be authorized to receive that FAR Part 121 credit from their respective POI. This is necessary even though the TCAS training may already be FAA-approved for the other operator, training center, or nanufacturer conducting the training. POI's may permit credit for use of other operator or training center programs if those programs have been approved by FAA and if aircraft, TCAS systems, procedures, and other relevant factors or circumstances are the same or equivalent to those of the operator seeking credit. If a POI is uncertain about the suitability of a proposed program for a particular TCAS system or aircraft type, the POI should consult, chrough established organizational procedures, with the appropriate division of the Flight Standards Service, the NSET, or the assigned AEG, as applicable.
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b. TCAS Academic Training. The following subjects should be addressed in an approved program of TCAS academic training during the initial introduction of a crewmember to TCAS. For subsequent programs, only the new, revised, or emphasis items need be addressed, as appropriate.
(1) General concepts of TCAS operation. TCAS academic training should cover, in general terms, TCAS system theory to the extent appropriate to ensure proper operational use. Aircrews should inderstand basic concepts of TCAS logic, closest point of approacn, tau, altitude separation thresholds for the issuance of RA's, as wel.
as the relationship between displayed traffic information and issuance of TA's and RA's. The training program should address the neaning of TA's and RA's: "increase," "reversal " "crossing," and "weakened" RA's; that TCAS II assures separation from Mode C-equipped aircraft; the detection provided by TCAS against altitude reporting and non-altitude reporting intruders; that the system detects multiple aircraft; TCAS-to-TCAS coordination; the potential impact of not following RA's; and the continued applicability of the "see and avoidi concept.
(2) Expected flightcrew response and level of protection provided by TCAS. Academic training should explain the normal, expected pilot response to TA's, to an RA, use of displayed traffic information to establish visual contact, and constraints on maneuvering based only on TA's.
(3) TCAS general limitations. There are several system limitations which apply to all aircraft types that should be understood as well as operational or performance limitations. System limitations include: the inability of TCAS to detect non-transponder-equipped aircraft, no RA's issued for traffic without an altitude reporting transponder, etc. Operational limitations include some RA's being inhibited at low altitudes, certain RA's being limited by aircraft performance constraints, and appropriate response to RA's in limiting performance conditions such as during heavy weight takeoff or while en route at maximum altitude for a particular weight.
(4) ATC Communication and Coordination. Training should discuss communication and coordination with ATC related to or following a TCAS event and when to contact ATC.
ICAS equipment components, controls, displays, audio alerts, and annunciations. Academic training should include aiscussion or TCAS terminology, symbology, operation, and optiona.
controls and display features including any items particular to ar air carrier's implementation or unique to its system.
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(6) Interfaces and compatibility with other aircraft systems. Training should discuss the role of Mode S transponder (with a correct, discreet address installed), radar altimeter inputs to ICAS, weather radar/electronic flight instrument system interfaces, including any items particular to an air carrier's implementation or unique to its system.
(7) Aircraft Flight Manual (AFM) information. AFM provisions should be addressed including information on TCAS modes of operation, normal and non-normal flightcrew operating procedures, and response to TA's, RA's, and any AFM limitations.
(8) MEL operating provisions.
(9) Appropriate pilot response to TCAS TA's, ATC clearance compliance, nuisance alerts, and other such issues.
(10) The air carrier's TCAS event reporting policies for Llightcrews.
(11) Procedures by which aircrews report TCAS malfunction recording procedures for TCAS system irregularities, if not otherwise addressed by routine maintenance procedures of that operator.
c. ICAS vaneuver Training. In addition to the academic training described in paragraph 8b, appropriate maneuver training is required, to ensure use of proper procedures and response to TCAS advisories.
As a minimum, TCAS maneuver training should expose the pilot to the encounter geometries involving two level aircraft; an intruder with a vertical rate; the TCAS aircraft with a vertical rate, parallel approach geometries, as well as multiple aircraft encounters; and should cover corrective, preventive, crossing, increase, reversal, and weakened RA's. In addition, training programs should cover the proper use of ICAS controls, procedures, and limitations; correct assessment of displays, aural advisories, and annunciations; timely and correct responses to ICAS RA's; appropriate interaction with ATC following an RA-induced deviation with return to an assigned ATC clearance unless given a subsequent change to clearance following a TCAS event; recognition of ICAS system failures; and ICAS issues unique to that air carrier, as necessary; Such training may be conducted using TCAS-equipped flight training devices or simulators, or by using suitable, computer-based instruction (CBI). Criteria for programs intending to address proper TCAS maneuvers through the use of simulators or training devices are listed in paragraph 8c(1).
Criteria for programs intending to address proper TCAS maneuvers through CBI, and not using approved simulators or training devices, are listed in paragraph 8c (2). operators may appiy provisions of either paragraph 8c(1) or 8c(2), or combinations of these provisions to address necessary initial and recurrent TCAS maneuver training, as 12