Appendix A A-3
• AC 91-70, Oceanic and Remote Continental Airspace Operations.
• AC 91-85, Authorization of Aircraft and Operators for Flight in Reduced Vertical Separation Minimum (RVSM) Airspace.
• AC 120-92, Safety Management Systems for Aviation Service Providers.
• AC 120-123, Flightpath Management.
4. Technical Standard Orders (TSOs) (available at https://drs.faa.gov):
• TSO-C112f, Air Traffic Control Radar Beacon System/Mode Select (ATCRBS/Mode S) Airborne Equipment.
• TSO-C118a, Traffic Alert and Collision Avoidance System (TCAS) Airborne Equipment, TCAS I.
• TSO-C119e, Traffic Alert and Collision Avoidance System (TCAS) Airborne Equipment, TCAS II with Hybrid Surveillance.
• TSO-C219a, Airborne Collision Avoidance System (ACAS) Xa/Xo.
Note: ACAS installations may have been previously issued a TSO Authorization (TSOA) or Letter of Deviation Authority (LODA) under TSO-C119a–d and the corresponding ATCRBS/Mode S TSO.
5. RTCA, Inc. Technical Standards Documents (available for purchase at https://my.rtca.org/nc__store):
• RTCA DO-181F as modified by Change 1, Minimum Operational Performance Standards for Air Traffic Control Radar Beacon System/Mode Select (ATCRBS/Mode S) Airborne Equipment.
• RTCA DO-185B, Minimum Operational Performance Standards for Traffic Alert and Collision Avoidance System II (TCAS II).
• RTCA DO-197A, Minimum Operational Performance Standards for an Active Traffic Alert and Collision Avoidance System I (Active TCAS I).
• RTCA DO-300A, Minimum Operational Performance Standards (MOPS) for Traffic Alert and Collision Avoidance System II (TCAS II) Hybrid Surveillance.
• RTCA DO-385A, Minimum Operational Performance Standards for Airborne Collision Avoidance System X (ACAS X) (ACAS Xa and ACAS Xo).
A.4 Accident History Related to the Development and Evolution of ACAS. This paragraph provides links to online information on significant historical accidents that have played a role in the development and evolution of ACAS. This paragraph does not provide a detailed narrative of those events, but rather enables interested readers to conduct further research into accidents that have influenced the development of ACAS by providing easy access to relevant information. The intent of providing links to this information is to provide access to historical lessons learned related to ACAS and to preserve key safety objectives for the system and facilitate its continued refinement.
Appendix A A-4
1. Pacific Southwest Airlines Flight 182 Boeing 727 collision with a Cessna 172, near San Diego, on September 25, 1978 (NTSB Report AAR-79/05).
2. Aéromexico Airlines Flight 498 McDonnell Douglas DC-9 collision with a Piper PA-28-181, near Los Angeles, on August 31, 1986 (NTSB Report AAR-87/07).
3. Saudi Arabian Airlines Flight 763 Boeing 747 collision with Kazakhstan Airlines Flight 1907 Ilyushin IL-76, near Charkhi Dadri, India, on November 12, 1996.
4. German Air Force Tupolev TU-154 collision with a United States Air Force (USAF) Lockheed C-141, near the coast of Namibia, on September 13, 1997.
5. DHL Flight 611 Boeing 757 midair collision with Bashkirian Airlines Flight 2937 Tupolev Tu-154, near Überlingen, Germany, on July 1, 2002 (German Federal Bureau of Aircraft Accidents Investigation BFU Report AX001-1-2/02).
6. GOL Linhas Aéreas Flight 1907 Boeing 737-800 collision with an Embraer Legacy 600, near Peixoto de Azevedo, MT, Brazil, September 29, 2006 (Aeronautical Accident Investigation and Prevention Center CENIPA A-022/CENIPA/2008).
Appendix A A-5 A.5 Acronyms.
Acronym Term 14 CFR Title 14 of the Code of Federal Regulations 49 CFR Title 49 of the Code of Federal Regulations 49 U.S.C. Title 49 of the United States Code AAUP Attention All Users Page AC Advisory Circular ACARS Aircraft Communications Addressing and Reporting System ACAS Airborne Collision Avoidance System (also known as TCAS) ACAS X Airborne Collision Avoidance System X ACAS Xa ACAS X variant using “active” interrogations (used for fixed-wing aircraft) ACAS Xo ACAS X variant used for “operations” (tailors the guidance for designated aircraft to an operation) AD Airworthiness Directive ADS-B Automatic Dependent Surveillance-Broadcast ADS-R Automatic Dependent Surveillance-Rebroadcast AED Aircraft Evaluation Division AFM Aircraft Flight Manual AFMS Aircraft Flight Manual Supplement AGL Above Ground Level AHRS Attitude and Heading Reference System AIM Aeronautical Information Manual AIP Aeronautical Information Publication AIR Aircraft Certification Service AOTO ADS-B Only TA-ONLY AP Autopilot ASAP Aviation Safety Action Program ASRS Aviation Safety Reporting System ATAS ADS-B Traffic Advisory System ATC Air Traffic Control ATCRBS ATC Radar Beacon System CAA Civil Aviation Authority
Appendix A A-6 Acronym Term CAS Collision Avoidance System CBT Computer-Based Training CH Certificate Holder CMO Certificate Management Office CMT Certificate Management Team CPA Closest Point of Approach CRM Crew Resource Management CSPO Closely Spaced Parallel Operations DAA Detect and Avoid DMOD Distance Modification DNA Designated No Alert DRS Dynamic Regulatory System EFIS Electronic Flight Instrument Systems ERC Event Review Committee ES Extended Squitter FAA Federal Aviation Administration FD Flight Director FL Flight Level FLT ID Flight Identification FOEB Flight Operations Evaluation Board fpm Feet Per Minute FS Flight Standards FSB Flight Standardization Board FSBR Flight Standardization Board Report FSDO Flight Standards District Office FSS Flight Service Station FSTD Flight Simulation Training Device FTD Flight Training Device g Gravitational acceleration of 9.81 meters per second2 GA General Aviation GNSS Global Navigation Satellite System
Appendix A A-7 Acronym Term HMD Helmet-Mounted Display HMD Horizontal Miss Distance HS Hybrid Surveillance HUD Head-Up Display HURS High Update Rate Surveillance ICAO International Civil Aviation Organization IFR Instrument Flight Rules IMC Instrument Meteorological Conditions inHg Inches of Mercury IRS Inertial Reference System LOA Letter of Authorization LODA Letter of Deviation Authority LOFT Line-Oriented Flight Training mb Millibars MEL Minimum Equipment List MHz Megahertz MMEL Master Minimum Equipment List Mode S Mode Select MOPS Minimum Operational Performance Standards MOR Mandatory Occurrence Report MRB Maintenance Review Board MRBR Maintenance Review Board Report MSpec Management Specification NAS National Airspace System NASA National Aeronautics and Space Administration NM Nautical Mile NMAC Near Midair Collision NSP National Simulator Program NTSB National Transportation Safety Board OpSpec Operations Specification PAI Principal Avionics Inspector
Appendix A A-8 Acronym Term PF Pilot Flying PFD Primary Flight Display PI Principal Inspector PL Policy Letter PM Pilot Monitoring PMI Principal Maintenance Inspector POI Principal Operations Inspector PRM Precision Runway Monitor QFE The atmospheric pressure at aerodrome elevation (or at runway threshold) QNE The barometric pressure used for the standard altimeter setting (29.92 inHg) QNH The barometric pressure as reported by a particular station RA Resolution Advisory RBDM Risk-Based Decision Making RVSM Reduced Vertical Separation Minimum RWC Remain Well Clear SA Safety Assurance SAFO Safety Alert for Operators SDP Standard Datum Plane SDR Service Difficulty Report SL Sensitivity Level SMS Safety Management System SRM Safety Risk Management SSR Secondary Surveillance Radar STBY Standby STC Supplemental Type Certificate TA Traffic Advisory Tau (τ) Time to Closest Point of Approach TAWS Terrain Awareness and Warning System TC Type Certificate TCAS Traffic Alert and Collision Avoidance System (also known as ACAS) TFC Traffic
Appendix A A-9 Acronym Term TOPA TCAS Operational Performance Assessment TSO Technical Standard Order TSOA Technical Standard Order Authorization UAT Universal Access Transceiver USAF United States Air Force UTC Universal Coordinated Time VFR Visual Flight Rules VMD Vertical Miss Distance VSI Vertical Speed Indicator XPDR Transponder ZTHR Altitude Threshold (Z-axis Threshold) A.6 Definitions.
A.6.1 Active Surveillance. Using ACAS interrogations and subsequent replies to update or acquire an ACAS track.
A.6.2 Airborne Collision Avoidance System (ACAS). A family of airborne devices meeting specified TSO and RTCA requirements that function independently of the ground-based ATC system to provide collision avoidance information.
A.6.2.1 ACAS I. An ACAS providing only TAs to assist pilots in the visual acquisition of intruder traffic. TCAS I is currently the only example of a developed ACAS I.
A.6.2.2 ACAS II. An ACAS that provides TAs and RAs, including vertical maneuvers that should or should not be performed to attain or maintain minimum safe vertical separation from a threat aircraft. TCAS II and ACAS Xa are currently the only examples of an ACAS II.
A.6.2.3 ACAS III (in development). An ACAS that provides TAs and RAs, including vertical and horizontal maneuvers that should or should not be performed to attain or maintain minimum safe separation from a threat aircraft.
A.6.3 ACAS II Maneuver Training. Part of flight training that includes the integration of ACAS II knowledge with the specific skills required to demonstrate satisfactory performance of a particular ACAS II procedure or maneuver, or series of procedures or maneuvers.
Appendix A A-10 A.6.4 A CAS Academic Training (as applied herein) . Part of ground training that exclusively addresses acquiring the required ACAS concepts, systems, limitations, or procedures knowledge (rather than skills), and demonstration of that knowledge. ACAS academic training generally is accomplished using a combination of classroom methods (standup instruction, computer-based instruction, tutorial, etc.), flight manual information bulletins, or self-study.
A.6.5 ACAS E vent. For the purpose of this AC, one or more of the following occurrences or situations are related to ACAS:
A.6.5.1 ACA S II Resolution Advisory (RA) or Traffic Advisory (TA). Issuance of any ACAS II RA or TA as specified by a flightcrew.
A.6.5.2 In-Flight Traffic Conflicts. Other ACAS-related in-flight traffic conflicts or potential conflicts as determined by a flightcrew.
A.6.5.3 Near Midair Collision (NMAC). NMACs involving an ACAS-equipped aircraft.
A.6.5.4 System Error. ATC system error involving an ACAS-equipped aircraft.
A.6.5.5 System Failures. System failures related to a traffic conflict, potential traffic conflict situation, or ACAS general system performance.
A.6.5.6 System Safety Performance. Other ACAS occurrences or situations related to potential ACAS or ATC system safety performance.
A.6.6 A ircraft Certification Service (AIR) Office. The FAA offices responsible for oversight of design, production, airworthiness certification, and continued airworthiness programs for all U.S. civil aviation products and foreign import products.
A.6.7 Aircraft Evaluation Division (AED). The FAA offices that contribute an operational perspective to engineering activities and identify applicable operating regulations. In certification projects, a primary responsibility of AED is to evaluate, as appropriate, flightcrew type rating requirements, minimum equipment required for dispatch, and continued airworthiness. AED provides consultation, coordination, and assistance to AIR in certification programs and the development of Airworthiness Directives (AD).
A.6.8 Air Traffic Control Radar Beacon System (ATCRBS). Secondary surveillance radar system with ground-based interrogators and airborne transponders capable of operation on Modes A and C.
A.6.9 Altitude Threshold (ZTHR). The projected minimum altitude threshold or Z-ax is Threshold (ZTHR) for the issuance of a preventive RA. The ZTHR varies with aircraft altitude.
A.6.10 Automatic Dependent Surveillance-Br oadcast (ADS-B). A function on an aircraft or vehicle that automatically broadcasts its own-ship identity, state vector (horizontal and
Appendix A A-11 vertical position and velocity), associated quality and performance parameters (accuracy and integrity), and other information. Broadcast links include the 1090 MHz Extended Squitter (ES) and the UAT broadcast on 978 MHz.
A.6.11 Bearing. The angle of another aircraft in the horizontal plane, measured clockwise from the longitudinal axis of own-ship.
A.6.12 Closest Point of Approach (CPA). The occurrence of minimum range between own-ship and another aircraft.
A.6.13 Coast. Condi tion that occurs when ACAS does not receive a reply to an interrogation from an aircraft where ACAS has established a track, resulting in the logic continuing the track based on previous track characteristics.
A.6.14 Coordination (as related to ACAS II). The process where A CAS II units in conflicting aircraft operating in TA/RA mode communicate with one another to generate complementary RAs to resolve an encounter (e.g., one ACAS generates a climb RA, and the other ACAS generates a descend RA).
A.6.15 Discrete. Separate, complete, and distinct signal.
A.6.16 Encounter. A situation when two or more aircraft are in proximity to each other so that an RA is generated on at least one of them.
A.6.17 False Advisory. An advisory determined by postevent analysis to have been caused by a false track or an ACAS malfunction.
A.6.18 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. FSBs are established for each large turbojet, turboprop, and special 14 CFR § 21.41 airplane type used in air transportation, as well as other 14 CFR part 25 airplanes, transport category multiengine helicopters, and large multiengine piston airplanes.
A.6.19 Flight Standards District Office (FSDO). A Flight Standards (FS) office staffed with personnel who serve the aviation industry and the public on matters relating to the certification and operation of air carriers and General Aviation (GA) aircraft.
A.6.20 Follow-On Supplemental Type Certificate (STC) (as related to ACAS). The following examples are follow-on STCs:
A.6.20.1 AC AS II Installation. A previously approved ACAS II installation that is installed in a subsequent type or model aircraft.
A.6.20.2 Display Configuration. Changes of display configuration; weather radar/ACAS display; supporting system inputs, such as radar altimeter; or other aircraft interfaces, such as TAWS, etc.
Appendix A A-12 A.6.21 Horizontal Miss Distance (HMD). The horizontal range between two aircraft at the CPA.
A.6.22 Hybrid Surveillance (HS). Combined use of active and passive surveillance to update an ACAS track.
A.6.23 Initial Type Certificate (TC)/Supplemental Type Certificate (STC) (as related to ACAS).
The first FAA ACAS airworthiness approval in accordance with a TC or an STC of any one or combination of the following components: an ACAS processor (computer), a directional antenna, and/or a Mode S transponder.
A.6.24 Intruder. A n aircraft that has satisfied the ACAS TA generation criteria.
A.6.25 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. Responsible Flight Standards offices apply MRB requirements in reviewing and approving the maintenance program of an air carrier.
A.6.26 Master Minimum Equipment List (MMEL). An FAA document listing stipulation that may provide authorization for the continuation of flight beyond a terminal point with certain inoperative equipment. AED develops MMELs in conjunction with an FOEB established for each aircraft type. FAA MMELs serve as the basis for an operator to develop specific MELs applicable to its particular aircraft and operational requirements.
A.6.27 Mode A. ATCRBS S SR equipment or mode of operation that replies to interrogations with a 4-digit transponder code with 4,096 possible codes (non-altitude reporting).
A.6.28 Mode C. ATCRBS SS R equipment or mode of operation that replies to interrogations with aircraft pressure altitude information.
A.6.29 Mode S. Mode Select (S), SS R equipment, or mode of operation that replies to interrogations with transponder code, aircraft pressure altitude information, a discrete address, and other aircraft information.
A.6.30 Multiple Threat Encounter. An e ncounter involving two or more threats against own-ship being processed simultaneously by the ACAS.
A.6.31 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, human resources, and material; and system components shared jointly with the military.
A.6.32 National Simulator Program (NSP). Program consisting of simulator evaluation specialists responsible for evaluating FSTDs to aid the POI in approving use of a specific FSTD in a training program.
Appendix A A-13 A.6.33 Other Traffic. A n aircraft that is more than 6 nautical miles (NM) laterally or more than 1,200 feet vertically from own-ship.
A.6.34 Passive Surveillance. The use of ADS-B Out pos ition messages to update the ACAS track of other aircraft.
A.6.35 Pressure Altitude. The height above a Standard Datum Plane (SDP), a theoretical level where the weight of the atmosphere is 29.92 inches of mercury (inHg)/1013.25 millibars (mb). Aircraft transponders transmit and ACAS uses pressure altitude so that ACAS can function correctly with relative altitude between aircraft regardless of the barometric scale setting of the altimeter. When an aircraft is below Flight Level (FL) 180, ATC automation corrects the pressure altitude received from the transponder for nonstandard pressure to display the estimated indicated altitude of the aircraft to the controller.
A.6.36 Principal Inspector (PI). Refers to one of the following three FAA inspectors who is selected as primary for an air carrier:
A.6.36.1 Prin cipal Avionics Inspector (PAI). The FAA inspector responsible for overseeing all avionics issues relative to a specific operator, including input on training programs, OpSpecs, MEL requests, etc.
A.6.36.2 Principal Maintenance Inspector (PMI). The FAA inspector responsible for overseeing all maintenance issues relative to a specific operator, including input on training programs, OpSpecs, MEL requests, etc.
A.6.36.3 Principal Operations Inspector (POI). The FAA inspector responsible for overseeing all operational issues relative to a specific operator, including training programs, OpSpecs approval, MEL approval requests, etc.
A.6.37 Proximate Traffic. Tr affic shown on the traffic display that is within 6 NM laterally and 1,200 feet vertically of own-ship that does not meet the threshold for a TA or an RA.
A.6.38 Relative Altitude. The d ifference in altitude between own-ship and another aircraft. The value is positive when the other aircraft is higher and negative when the other aircraft is lower.
A.6.39 Resolution Advisory (RA). Aura l voice and display information provided by ACAS II to a flightcrew, advising that a particular maneuver should or should not be performed to attain or maintain minimum safe vertical separation from a threat aircraft.
A.6.39.1 Altitud e Crossing RA. An RA that directs a flightcrew to cross through the altitude of a threat aircraft to achieve safe vertical separation.
A.6.39.2 Coordinated Crossing RA. Initial RA coordinated between aircraft operating ACAS II and that direct the aircraft to cross in altitude.
Appendix A A-14 A.6.39.3 Corrective RA. An RA that advises the flightcrew to either deviate from current vertical speed, such as climb when the aircraft is level, or to maintain an existing climb or descent rate.
A.6.39.4 Increase Rate RA. An RA that is issued after an initial climb or descend RA that indicates additional climb or descent rate is required to achieve safe vertical separation. An increase rate RA requires a climb or descent rate of 2,500 fpm.
A.6.39.5 Initial RA. First RA generated during an encounter.
A.6.39.6 Preventive RA. An RA that requires a flightcrew to avoid certain deviations from current vertical rate, such as a do not climb RA when the aircraft is level.
A.6.39.7 Reversal RA. An RA that indicates a change in the direction previously generated by ACAS II and that is required to achieve safe vertical separation
(e.g., an initial descend RA that reverses to a climb RA).
A.6.39.8 Subsequent RA. A modified RA generated during an encounter after the initial RA but before a “Clear of Conflict” annunciation. Subsequent RAs may be weakened, strengthened, or reversed.
A.6.39.9 Weakened RA. An initial corrective RA that changes to an RA calling for a return to level flight because ACAS II has determined that safe vertical separation is projected (e.g., a climb RA weakens to a do-not-descend advisory once the desired vertical separation has been achieved).
A.6.40 Sense. A direction that an RA may take (either cli mb or descend) relative to the existing flight path of own-ship.
A.6.41 Significant ACAS Events. Si gnificant ACAS events are those that meet any one of the following guidelines:
A.6.41.1 Altitu de Excursion. There is an altitude excursion of more than 1,000 feet from an assigned level altitude.
A.6.41.2 Coordinated Crossing RA. ACAS II generates a coordinated crossing RA.
A.6.41.3 Descent RA. ACAS II generates a descent RA when own-ship is below 1,000 feet AGL.
A.6.41.4 Performance. ACAS is suspected of not performing as designed.
A.6.41.5 Reversal RA. ACAS II generates a reversal RA.
A.6.41.6 Loss of Standard Air Traffic Control (ATC) Separation. There is a loss of standard ATC separation resulting from compliance with an ACAS II-generated RA.