Airborne Collision Avoidance System (ACAS)

Traffic Alert and Collision Avoidance System (TCAS)

Airborne Collision Avoidance System (ACAS) was developed as a safety-enhancing system to reduce the likelihood of mid-air collisions between aircraft. ACAS is a family of airborne devices that function independently of the ground-based Air Traffic Control (ATC) system and provides collision avoidance for a broad spectrum of aircraft types.

ACAS iterations include Traffic Alert and Collision Avoidance System (TCAS) I, TCAS II, and ACAS Xa. TCAS I provides Traffic Advisories (TAs) that indicate on a display the positions and relative altitudes (if the target is altitude reporting) of transponder operating aircraft to assist a flightcrew in the visual acquisition of aircraft with a potential for collision. 
ACAS II (TCAS II or ACAS Xa) provides both TAs and Resolution Advisories (RAs). RAs are recommended vertical maneuvers, or vertical maneuver restrictions that maintain or increase the vertical separation between aircraft for collision avoidance. 

With the introduction of ACAS Xa, the FAA now permits four variants of ACAS II in U.S. airspace, TCAS II version 6.04a, TCAS II version 7.0, TCAS II version 7.1, and ACAS Xa including optional ACAS Xo features. If an aircraft has an ACAS II installed, it must be TCAS version 7.0, version 7.1, or ACAS Xa to operate within Reduced Vertical Separation Minimum (RVSM) airspace.

Operators flying outside of U.S. territorial airspace are advised to ensure that appropriate ACAS software updates are incorporated for compatibility with oceanic and international equipage and operation standards for ACAS. International requirements differ by type of operation, type of aircraft, and airspace entry requirements. Consult documents of ICAO and the Aeronautical Information Publication (AIP) of the Civil Aviation Authority (CAA) with jurisdiction of the airspace to be flown for more information.

Below you will find links to ACAS regulations and guidance, as well as detailed information on the airspace and equipment requirements and capabilities.

Number Title
49 U.S.C § 44716 Collision Avoidance System
14 CFR § 91.123 Compliance with ATC Clearances and Instructions
14 CFR § 91.221 Traffic Alert and Collision Avoidance System Equipment and Use
14 CFR § 91.1045 Additional Equipment Requirements
Appendix G to Part 91 Operations in Reduced Vertical Separation Minimum (RVSM) Airspace
14 CFR § 121.356 Collision Avoidance System
14 CFR § 125.224 Collision Avoidance System
14 CFR § 129.18 Collision Avoidance System
14 CFR § 135.180 Traffic Alert and Collision Avoidance System
49 CFR § 830.5 Immediate Notification

Advisory Circulars (AC)

Number Title
120-55C (Change 1) Air Carrier Operational Approval and Use of TCAS II
20-131A Airworthiness Approval of Traffic Alert and Collision Avoidance Systems (TCAS II) and Mode S Transponders
20-151C Airworthiness Approval of Traffic Alert and Collision Avoidance Systems (TCAS II), Versions 7.0 & 7.1 and Associated Mode S Transponders

Related Safety Alerts for Operators (SAFOs) and Information for Operators (INFOs)

Number Title
SAFO 22003 Traffic Alert and Collision Avoidance System II (TCAS II) Alerts at Denver International Airport (DEN)
SAFO 11010 TCAS II Guidance and Training for Title 14 of the Code of Federal Regulations (14 CFR) Part 135 & Part 125 Certificate Holders, Part 125 Letter of Deviation Authority (LODA) holders (125M), Part 91 Subpart K, (91K) Program Managers, Part 91 Operators and Part 142 Training Centers.
InFO 23010 Planned Implementation of 3° Lateral Offset Approaches Serving Runway 16R at Denver International Airport (KDEN) to Reduce Traffic Alert and Collision Avoidance System (TCAS) Resolution Advisories (RA) with Runway 16L Approaches.
InFO 08039 Responding to a TCAS resolution advisory (RA) – Fly the RA
InFO 08006 Prompt recognition of TCAS functionality issues

Other Information and Guidance

Number Title
FAA Booklet HQ-111358 Introduction to TCAS II Version 7.1
TSO-C118a Traffic Alert and Collision Avoidance System (TCAS) Airborne Equipment, TCAS I
TSO-C119e (Historical) Traffic Alert and Collision Avoidance System (TCAS) Airborne Equipment, TCAS II with Hybrid Surveillance
TSO-C219a Airborne Collision Avoidance System (ACAS) Xa/Xo
RTCA DO 185B Minimum Operational Performance Standards for TCAS II
RTCA DO 300A Minimum Operational Performance Standards for Traffic Alert and Collision Avoidance System (TCAS II) Hybrid Surveillance
RTCA DO 385A Minimum Operational Performance Standards for Airborne Collision Avoidance System X (ACAS X) (ACAS Xa and ACAS Xo), Volume I and Volume II.
ICAO DOC 9863 Airborne Collision Avoidance System (ACAS) Manual
ICAO Appendix 6, Part 1 International Commercial Air Transport Aeroplanes
ICAO Appendix 6, Part 2 International General Aviation Aeroplanes
ICAO Annex 10, Volume IV Surveillance and Collision Avoidance Systems, ACAS Standards and Recommended Practices (SARPs)
FAA Order 8900.1, Vol.3, Ch.19, § 8 Flightcrew Member Training and Qualification Programs, Special Training

Focal Point:  Flight Technologies and Procedures Division, Flight Operations Group (AFS-410)
Email: 9-AWA-AVS-AFS-400-Flight-Technologies-Procedures@faa.gov  
 

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