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Significant Regulatory Guidance

Letter to Airport Sponsors about Using UAS to Disperse Wildlife

Aeromedical Collaboration Outreach

FAA Office of Aerospace Medicine
Civil Aerospace Medical Institute

Report No: DOT/FAA/AM-23/29

Title and Subtitle:Aeromedical Collaboration Outreach

Report Date: September 2023

Authors:Dienst J, Sienknecht T, Graf V, Lehner B, Roessner S

Abstract: The FAA Office of Aerospace Medicine (AAM) tasked MITRE's Center for Advanced Aviation...

Exploring Industry Medical Risk Management Best Practices for Application to Aerospace Medicine

FAA Office of Aerospace Medicine
Civil Aerospace Medical Institute

Report No: DOT/FAA/AM-23/24

Title and Subtitle:Exploring Industry Medical Risk Management Best Practices for Application to Aerospace Medicine

Report Date: July 2023

Authors:R. Lieberthal, I. Catovic, C. Mills, G. Chesterton

Abstract: The Federal Aviation...

Designing an NHTSA Crash Injury Research Analog Program for General Aviation / Advanced Air Mobility

FAA Office of Aerospace Medicine
Civil Aerospace Medical Institute

Report No: DOT/FAA/AM-23/23

Title and Subtitle:Designing an NHTSA Crash Injury Research Analog Program for General Aviation / Advanced Air Mobility

Report Date: July 2023

Authors:Lauren A. Collins

Abstract: The MITRE Corporation was tasked by the Federal Aviation...

Aircraft Wake Turbulence

Friday, March 06, 2026

Wake Vortex Encounter - Mitigation

Wake vortices are masses of counter-rotating air created as a by-product of the generation of lift. Every aircraft that uses a fixed or rotary airfoil to generate lift in flight creates wake vortices of varying initial strength and persistence. Wake vortices from similar or larger size generating (lead) aircraft are a hazard to encountering (following) aircraft that may vary from light turbulence encounters to a Loss of Control-Inflight or in-flight breakup accident.

Pilots are advised to:

Learn to visualize the behavior, location, and movements of wake vortices from similar or larger size generating aircraft.
Proactively adjust their flight path or delay operations as needed to avoid or mitigate a wake vortex encounter.
Be alert for possible wake vortex encounters, particularly during takeoff, approach, and landing operations.
Follow the wake vortex encounter avoidance and mitigation guidance contained in AC 90-23 as amended, applicable aircraft manuals, and the Aeronautical Information Manual (AIM).

Pilots have the ultimate responsibility for the safe operation of their aircraft. Pilots arriving and departing from uncontrolled airports, or accepting a clearance for a visual approach, operating using Visual Flight Rules (VFR) outside of controlled airspace are accepting the responsibility for wake vortex encounter avoidance and mitigation. When Air Traffic Control (ATC) is providing separation services, the controller shares in this responsibility. ATC mitigates wake vortex encounter risk through minimum separation standards between leader aircraft and follower aircraft, as well as information reports to pilots such as Wake Turbulence Cautionary Advisories.

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

Advisory Circulars (AC)

Number	Title
AC 90-23H	Aircraft Wake Vortex Encounter Risk Mitigation

Other Information and Guidance

Number	Title
Aeronautical Information Manual (AIM)	Chapter 7 Section 4. Wake Turbulence
Wake Turbulence Training Aid	FAA Wake Turbulence Training Aid
ICAO AUPRTA	Airplane Upset Prevention & Recovery Training Aid (Rev 3)
JO 7360.1 (as revised)	Aircraft Type Designators
JO 7110.65 (as revised)	Air Traffic Control

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

Airborne Collision Avoidance System (ACAS)

Monday, September 29, 2025

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 Enhanced, 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.

Regulations

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 § 91.227	Automatic Dependent Surveillance-Broadcast (ADS-B) Out equipment performance requirements.
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
Appendix B to Part 121	Airplane Flight Recorder Specification
14 CFR § 125.224	Collision Avoidance System
Appendix D to Part 125	Airplane Flight Recorder Specification
14 CFR § 129.18	Collision Avoidance System
14 CFR § 135.180	Traffic Alert and Collision Avoidance System
Appendix D to Part 135	Airplane Flight Recorder Specification
49 CFR § 830.5	Immediate Notification

Advisory Circulars (AC)

Number	Title
90-120	Operational Use of Airborne Collision Avoidance Systems
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

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 Annex 6, Part 1	International Commercial Air Transport Aeroplanes
ICAO Annex 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