# AC 90-23H: Aircraft Wake Vortex Encounter Risk Mitigation - Type: Advisory circular (guidance, not mandatory unless a rule or AD requires it) - Status: Current - Approved: January 13, 2026 - Family: AC 90-23 - Pages: 43 - FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/DRSDOCID134125902320260114142251.0001 - Page: https://openairdocs.org/ac/90-23 ## Versions - AC 90-23H (Current), approved Jan 13, 2026 - AC 90-23G (Historical), approved Feb 10, 2014 - AC 90-23F (Historical), approved Feb 20, 2002 - AC 90-23E (Historical), approved Oct 1, 1991 ## Text ### Page 1 U.S. Department of Transportation Federal Aviation Administration Advisory Circular Subject: Aircraft Wake Vortex Encounter Risk Mitigation Date: 1/13/26 AC No: 90-23H Initiated by: AFS-400 Change: This advisory circular (AC) presents basic information on wake vortex characteristics, alerts pilots to the hazards of aircraft wake vortex encounters, recommends operational procedures to avoid wake vortex encounters, and provides wake vortex encounter guidance. The contents of this document do not have the force and effect of law and are not meant to bind the public in any way, and the document is intended only to provide information to the public regarding existing requirements under the law or agency policies. Rober t Reckert for Hugh Thomas Acting Executive Director, Flight Standards Service ### Page 2 ii CONTENTS Paragraph Page 1 Purpose of This Advisory Circular (AC) … 1 2 Audience … 1 3 Where You Can Find This AC … 1 4 What This AC Cancels … 1 5 Summary of Changes … 1 6 Introduction … 1 6.1 Pilot Role in Wake Vortex Encounter Mitigation … 2 7 Wake Vortex Characteristics … 2 7.1 Wake Vortex Generation … 2 7.2 Wake Vortex Strength … 5 7.3 Wake Vortex Decay … 6 7.4 Wake Vortex Movement … 6 8 Wake Vortex Encounter Risk … 9 8.1 Factors Affecting the Likelihood of a Wake Vortex Encounter … 9 8.2 Factors Affecting the Severity of a Wake Vortex Encounter … 10 8.3 Angle of Wake Vortex Encounter … 12 8.4 Encountering Aircraft Energy State … 13 8.5 Pilot Influence on Likelihood and Severity of a Wake Vortex Encounter … 14 9 Wake Vortex Encounter Mitigations … 14 9.1 Departures … 14 9.2 Arrivals … 19 9.3 En Route … 25 9.4 Wake Vortex Encounter Mitigations for Generating Aircraft … 26 9.5 Wake Vortex Encounter Mitigations Utilized by ATC … 27 10 Wake Vortex Encounter Recovery Guidance … 29 10.1 Situational Awareness … 29 10.2 Startle and Surprise … 30 10.3 Flight Control Inputs … 30 ### Page 3 iii 10.4 Other Upset Recovery Considerations … 31 11 Pilot Wake Vortex Encounter Reporting … 32 11.1 Reporting to ATC … 32 11.2 Aviation Safety Reporting System (ASRS) … 32 11.3 Operator Reporting Policies … 33 11.4 FAA Hotline … 33 11.5 Notification of Aircraft Accidents or Incidents … 33 Appendix A. Administrative Information … A-1 Appendix B. Miscellaneous ATC Wake Separation Efforts … B-1 List of Figures Figure 1. Wake Vortices … 1 Figure 2. Wake Vortex Generation … 2 Figure 3. Touchdown and Rotation Points … 3 Figure 4. Rotorcraft Downwash and Outwash … 3 Figure 5. Rotorcraft Accelerating from a Hover … 4 Figure 6. Rotorcraft Approach to an Airport … 5 Figure 7. Wake Vortex Drift … 6 Figure 8. Wake Vortex Sink … 7 Figure 9. Wake Vortex Drift With Zero Crosswind … 7 Figure 10. Wake Vortex Drift With 3 Knots of Crosswind … 8 Figure 11. Wake Vortex Drift With 6 Knots of Crosswind … 8 Figure 12. Light Quartering Tailwind Wake Vortex Hazard … 9 Figure 13. Climbing Aircraft Wake Vortex Sink … 10 Figure 14. Loss of Control in Flight … 11 Figure 15. Counter Roll Control … 11 Figure 16. Axial Wake Vortex Encounter … 12 Figure 17. Air Movement Within Wake Vortices … 13 Figure 18. Crossing Wake Vortex Encounter … 13 Figur e 19. Departure Flightpath … 15 Figure 20. Opposite Direction Departure … 16 Figure 21. Intersection Departure … 17 ### Page 4 iv Figure 22. Crossing Departures … 17 Figure 23. Missed Approach Wake Vortices … 18 Figure 24. Departures From Adjacent Airports … 18 Figure 25. Avoiding Rotorcraft Downwash and Outwash … 19 Figure 26. Landing After a Larger Aircraft … 21 Figure 27. Parallel Runways With Threshold Stagger … 22 Figure 28. Landing After a Departing Aircraft … 22 Figure 29. Landing After a Crossing Runway Departure (Rotation Point Before Intersection) … 23 Figure 30. Landing After a Crossing Runway Departure (Rotation Point After Intersection) … 23 Figure 31. Landing After an Arriving Aircraft on a Converging Runway … 24 Figure 32. Arrival at an Adjacent Airport … 25 Figure 33. Opposing Flightpaths … 26 Figure 34. In-Trail Flightpath … 26 ### Page 5 1 1 PURPOSE OF THIS ADVISORY CIRCULAR (AC). This AC presents basic information on wake vortex characteristics, alerts pilots to the hazards of aircraft wake vortex encounters, recommends operational procedures to avoid wake vortex encounters, and provides wake vortex encounter guidance. Note: This is a guidance document. Its content is not legally binding in its own right and will not be relied upon by the Department as a separate basis for affirmative enforcement action or other administrative penalty. Conformity with the guidance document is voluntary only. Nonconformity will not affect rights and obligations under existing statutes and regulations. 2 AUDIENCE. This AC is intended to provide guidance on wake vortex encounters to student pilots, certificated pilots, flight instructors, training providers, and pilot examiners. 3 WHERE YOU CAN FIND THIS AC. You can find this AC on the Federal Aviation Administration’s (FAA) website at https://www.faa.gov/regulations_policies/advisory_cir culars and the Dynamic Regulatory System (DRS) at https://drs.faa.gov. 4 WHAT THIS AC CANCELS. AC 90-23G, Aircraft Wake Turbulence, dated February 10, 2014, is canceled. 5 SUMMARY OF CHANGES. This AC has been reorganized to assist pilots in effective Risk-Based Decision Making (RBDM) as it relates to wake vortex encounters. 6 INTRODUCTION. Wake vortices are masses of counter-rotating air created as a byproduct 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-sized (i.e., similar characteristics of weight, wingspan, etc.) or larger-sized generating (lead) aircraft, are a hazard to encountering (following) aircraft that may vary from light turbulence encounters to a loss of control in flight (LOC-I) or in-flight breakup accident. The purpose of this AC is to discuss the behavior, risk, and mitigation techniques for wake vortices. See Figure 1, Wake Vortices. Figure 1. Wake Vortices ### Page 6 6.1 Pilot Role in Wake Vortex Encounter Mitigation. In accordance with Title 14 of the Code of Federal Regulations (14 CFR) § 91.3(a), the pilot in command (PIC) of an aircraft is directly responsible for, and is the final authority as to, the operation of that aircraft. This responsibility includes wake vortex encounter avoidance and mitigation. Pilots arriving and departing from uncontrolled airports, flying in uncontrolled airspace, or accepting a clearance for a visual approach are accepting the sole responsibility for wake vortex encounter mitigation. Pilots are encouraged to: • Learn to visualize the behavior, location, and movements of wake vortices from similar or larger-sized generating aircraft. • Proactively adjust their flightpath 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 this AC, applicable aircraft manuals, and the Aeronautical Information Manual (AIM). **7 WAKE VORTEX CHARACTERISTICS.** 7.1 Wake Vortex Generation. Lift is generated by the creation of a pressure differential above and below the airfoil (e.g., wing or rotor). Higher-pressure air below the airfoil seeks to equalize the differential by moving towards the lower-pressure air above. This movement of air rolls upwards and inwards to form two counter-rotating cylindrical vortices trailing behind the airfoil. The disturbed air surrounding the wake vortices is the wake flow field. Studies conducted during approach and landing operations have not shown a discernible difference between the wake vortices of aircraft with and without winglets. See Figure 2, Wake Vortex Generation. Figure 2. Wake Vortex Generation ### Page 7 7.1.1 Rotation to Touchdown. Airfoils generate wake vortices whenever lift is produced. In airplanes, lift and wake vortices increase in strength substantially from the rotation point, the point where the airplane begins to lift off the surface, to the touchdown point, the point where the aircraft returns to the surface on landing. See Figure 3, Touchdown and Rotation Points. Figure 3. Touchdown and Rotation Points 7.1.2 Rotorc raft Downwash, Outwash, and Wake Vortices. The spinning rotor blades of helicopters and other rotorcraft, in a hover or slow hover taxi, generate a downward column of air called downwash. When a rotorcraft is in ground effect (i.e., usually less than one rotor diameter distance above the surface), the downward column of air interacts with the surface and produces outwash, a turbulent lateral movement of air. When a rotorcraft is in a hover in ground effect, outwash propagates in all lateral directions in still air. Tip vortices from the rotor blades are pushed down helically, coalesce as they approach the surface, and are driven outwards by the outwash intensifying the turbulent airflow. Downwash and outwash may damage aircraft below and in the vicinity of rotorcraft operations and may produce adverse effects on nearby aircraft operations, including turbulence and induced roll moments. See Figure 4, Rotorcraft Downwash and Outwash. Figure 4. Rotorcraft Downwash and Outwash ### Page 8 7.1.2.1 When a rotorcraft hovers into the wind or accelerates from a hover, the horizontal flow of air modifies the downwash. As the rotorcraft continues to accelerate, the rotor blades move into less disturbed air, and the downwash transitions to counter-rotating wake vortices. The forward flight speed of the rotorcraft in which the airflow transitions to counter-rotating wake vortices is dependent on multiple factors, including the type of rotorcraft and the environment that it is operating in. When a rotorcraft decelerates, the same forces are exerted in the reverse sequence. Rotorcraft wake vortices may have characteristics that differ from fixed-wing wake vortices (e.g., differing advancing and trailing blade vortices, separation between wake vortices differing when the rotorcraft is in a climb versus descent, etc.) due to the aerodynamic differences between a fixed and rotary airfoil. Rotorcraft wake vortex characteristics such as wake decay rate and wake drift have similar behaviors as wake vortices created by fixed-wing aircraft. 7.1.2.2 In terminal operations where a rotorcraft is arriving or departing, there is a combination of wake vortices, downwash, and outwash. Rotorcraft-generated turbulent airflows, including downwash, outwash, and wake vortices, are a hazard to following similar or smaller-sized aircraft, especially fixed-wing aircraft. Aircraft have suffered LOC-I accidents while attempting to arrive or depart an airport after a rotorcraft transited the area. See Figure 5, Rotorcraft Accelerating from a Hover, and Figure 6, Rotorcraft Approach to an Airport. Figure 5. Rotorcraft Accelerating from a Hover ### Page 9 5 Figure 6. Rotorcraft Approach to an Airport 7.2 Wak e Vortex Strength. The initial strength of wake vortices (i.e., strength of the wake vortices directly after wake generation) is influenced by the current weight, angle of attack (AOA), airfoil shape, wing loading or disk loading, and wingspan or rotor diameter of the generating aircraft. Wake vortices are the strongest in the immediate vicinity behind and below the generating aircraft and dissipate over time. The wake age (i.e., time elapsed since wake generation) influences the residual strength (i.e., remaining intensity of the wake vortices at a given time after generation). 7.2.1 Initial Strength. The greatest initial strength of a wake vortex nominally occurs when the generating aircraft is at a relatively high AOA, a heavy weight, and in a clean configuration (e.g., landing gear and wing flaps retracted). In the terminal environment, the greatest initial strength of a wake vortex occurs when the generating aircraft is at relatively low speeds. 7.2.1.1 “Super” (e.g., Airbus A380) and “Heavy” (e.g., Lockheed C-5) category aircraft, as defined by FAA Order JO 7360.1, Aircraft Type Designators, have been shown to produce high initial strength wake vortices that take longer to diminish due to the heavier weight and longer wingspan of these aircraft when compared to aircraft of smaller categories. ### Page 10 7.3 Wake Vortex Decay. The decay rate and movement of wake vortices is influenced by the initial strength of the wake vortices, the distance between the pair of wake vortices, and atmospheric conditions, including lateral wind speed and direction, vertical wind speed and direction, atmospheric turbulence, air density, and airmass stability. Considering a fixed wake vortex decay rate, time becomes the key variable. As time passes after wake generation, the residual strength of a wake vortex diminishes. 7.3.1 Environment Effects on Decay Rate. The environmental conditions that are the most conducive to a low wake decay rate are light winds, low atmospheric turbulence, and a stable airmass. The wake vortex decay rate tends to increase with an increase in wind speed, turbulence, or a decrease in airmass stability. 7.3.2 Aircraft Configuration Effects on Decay Rate. The extension of landing gear, wing flaps, or other wing configuring devices tend to change the wake vortex characteristics of an airplane. The extension of wing flaps tends to reduce the separation between vortices and hastens wake decay. The extension of landing gear tends to hasten the decay of vortices by creating turbulence that interacts with the wake flow field. 7.4 Wake Vortex Movement. Wake vortices nominally sink behind the generating aircraft and are influenced by the surrounding airmass characteristics, including vertical and horizontal winds that transport the vortices. Wake vortices tend to remain spaced apart slightly less than the wingspan of the generating aircraft, or the outboard edge of the wing flaps when deployed. When within ground effect (i.e., less than approximately a wingspan of the generating aircraft from the surface), the counter-rotating wake vortices tend to diverge laterally. See Figure 7, Wake Vortex Drift. Figure 7. Wake Vortex Drift 7.4.1 W ake Vortex Sink. Wake vortices tend to have the highest sink rate in the immediate vicinity behind the generating aircraft. Wake vortices from large aircraft may descend initially at a rate of several hundred feet per minute. The sink rate of the wake vortices tends to diminish as the wake age increases. Generally, for large generating aircraft, wake vortices tend to level approximately 500 to 900 feet below the flightpath of the generating aircraft. See Figure 8, Wake Vortex Sink. ### Page 11 7 Figure 8. Wake Vortex Sink 7.4.1.1 Wak e vortices from aircraft with high initial wake vortex strength, including “Heavy” and, especially, “Super” category aircraft, may descend more than 1,000 feet before decaying to a less perceptible residual strength. 7.4.1.2 After initially descending, several factors, including ambient thermal lifting, vertical winds, stratification, and interaction with the surface, may cause wake vortices to stop descending or even rise. This rising effect is commonly referred to as wake bounce and may result in wake vortices rising into the glidepath of an approach. 7.4.2 The Influence of Ground Effect on Wake Vortices. When wake vortices are in ground effect, the wake vortices tend to diverge laterally. In a zero-crosswind scenario, the wake vortices nominally diverge laterally at a speed of 2 to 3 knots. See Figure 9, Wake Vortex Drift With Zero Crosswind. Figure 9. Wake Vortex Drift With Zero Crosswind 7.4.2.1 W hen wake vortices are in ground effect, a light crosswind of approximately 3 knots tends to decrease the outward lateral movement of the upwind vortex and increase the outward lateral movement of the downwind vortex. This action results in the upwind vortex remaining near the glidepath and runway longer and displacing the downwind vortex at an increased rate. The downwind vortex may influence operations on an adjacent runway. See Figure 10, Wake Vortex Drift With 3 Knots of Crosswind. ### Page 12 8 Figure 10. Wake Vortex Drift With 3 Knots of Crosswind 7.4.2.2 S tronger crosswinds of 6 knots and above may displace one or both vortices to an adjacent runway. For example, a 6-knot crosswind component added to the downwind vortex nominally diverging laterally at 3 knots has a groundspeed of 9 knots. In this scenario, the downwind vortex displaces laterally 1,800 feet in 2 minutes. See Figure 11, Wake Vortex Drift With 6 Knots of Crosswind. Figure 11. Wake Vortex Drift With 6 Knots of Crosswind 7.4.2.3 A tailwind condition may force the wake vortices of a generating aircraft forward from where the vortices were generated, resulting in wake vortices closer to an approach glidepath than would otherwise occur in a no-wind scenario. 7.4.2.3.1 A light quartering tailwind may cause a hazardous landing condition for encountering aircraft. The crosswind component resists the upwind vortex tendency to move outwards and keeps the upwind vortex laterally near the approach and runway centerline while the tailwind component forces the wake vortices closer to the glidepath and further down the runway. See Figure 12, Light Quartering Tailwind Wake Vortex Hazard. ### Page 13 9 Figure 12. Light Quartering Tailwind Wake Vortex Hazard 8 WAK E VORTEX ENCOUNTER RISK. Wake vortices from a generating aircraft may pose a hazard to encountering aircraft of similar and smaller size. The risk of wake vortices is the composite of the likelihood and severity of an encounter. No two wake vortex encounters are identical due to the variables involved that affect both the likelihood and severity of an encounter. 8.1 Factors Affecting the Likelihood of a Wake Vortex Encounter. Wake vortices are generated with differing strengths and decay and drift at differing rates. The time between the generating aircraft and an encountering aircraft is a major factor for the likelihood of an encounter. The likelihood of a wake vortex encounter is dependent upon the proximity of the wake vortices to the flightpath of the potential encountering aircraft and the residual strength of the wake vortices at the time of intercept. The likelihood of a wake vortex encounter may increase when the following occurs: 8.1.1 The encountering aircraft is below the generating aircraft in trail or crosses below and behind the generating aircraft. This includes a generating aircraft climbing or descending in front of and through the flightpath of the encountering aircraft, or the encountering aircraft climbing or descending behind and through the flightpath of the generating aircraft. The closer the encountering aircraft is below and behind the generating aircraft in time and distance, the less time the wake vortex has had to decay and the higher the likelihood of an encounter. 8.1.2 The movement of the wake vortices, including lateral drift and vertical sink, may create scenarios where wake vortices are maintained in a critical area such as the glidepath or the runway, or both, for a longer period. Wake vortices may also drift or sink into adjacent aircraft operations. Examples of drift causing a higher likelihood of encounter include: ### Page 14 8.1.2.1 A light quartering tailwind that resists the outward movement of the upwind vortex and pushes the vortices forward in the approach and runway environment toward the touchdown zone (TDZ). 8.1.2.2 A light wind with a crosswind component of 1 to 5 knots that resists the outward movement of the upwind vortex causing the upwind vortex to remain in the final approach, runway, and TDZ area longer. The crosswind accelerates the downwind vortex away from the runway and, depending on conditions, towards an adjacent runway, approach, or departure area. 8.1.2.3 Wake vortices that may drift and sink into the takeoff or landing flightpaths of a crossing runway or into traffic patterns of adjacent airports. 8.1.2.4 Wake vortices that may sink into en route traffic, even when legally separated (e.g., aircraft separated by 500 feet vertically with an aircraft maintaining a 14 CFR § 91.159 visual flight rules (VFR) cruising altitude and an opposite direction aircraft maintaining a 14 CFR § 91.179 instrument flight rules (IFR) cruising altitude). Additional exposure may occur when a generating aircraft has transited in a climb or descent in front of the flightpath of an encountering aircraft (or the encountering aircraft climbs or descends behind the generating aircraft). See Figure 13, Climbing Aircraft Wake Vortex Sink. Figure 13. Climbing Aircraft Wake Vortex Sink 8.2 F actors Affecting the Severity of a Wake Vortex Encounter. Wake vortex encounters present a spectrum of severity that ranges from light turbulence to a LOC-I, or in-flight breakup. The turbulence generated by wake vortices may cause injuries to occupants of an encountering aircraft and may damage aircraft components and equipment. Wake vortices from a similar or larger-sized generating aircraft may induce a roll force or series of counter-rotating roll forces on an encountering aircraft that exceeds the counter roll authority (i.e., roll control used to counter the induced roll caused by a wake vortex). Wake vortex-induced roll forces exerted on an encountering aircraft may result in a situation where the pilot is required to perform an upset recovery. The severity of a wake vortex encounter is affected by the residual strength of the wake vortices at the point of encounter, the characteristics of the encountering aircraft, the encounter angle (i.e., the relative angle between the flightpath of the encountering aircraft and the wake vortex), ### Page 15 11 the energy state of the encountering aircraft, and the ability of the pilot to recover from a wake vortex encounter. See Figure 14, Loss of Control in Flight, and Figure 15, Counter Roll Control. Figure 14. Loss of Control in Flight Figu re 15. Counter Roll Control 8.2.1 Whe n the wake vortices residual strength is higher, the forces imparted on the encountering aircraft are higher. The residual strength of the wake vortex at the point of intercept with the encountering aircraft is a function of the amount of wake decay deducted from the initial wake strength. The amount of wake decay depends on the wake vortex age (i.e., time elapsed since wake vortex generation), and the effect of the environment that existed during that time. 8.2.2 The capability of an aircraft to counteract the wake-induced roll depends on the counter roll control and wingspan of the encountering aircraft. Encountering aircraft with a relatively short wingspan, even in a high-performance aircraft, tends to be influenced more by a wake vortex than an aircraft with a larger wingspan. Encounters where the wingspan and roll control surfaces of the encountering aircraft extend beyond the rotation ### Page 16 12 of the wake vortex, counter roll control is usually more effective, and the induced roll is decreased. 8.3 Angle of Wake Vortex Encounter. The relative angle between the flightpath of the encountering aircraft and the wake vortex influences the severity of the encounter. 8.3.1 If the encountering aircraft is in line (i.e., in-trail or passing below the generating aircraft) or converging at a shallow angle with the wake vortices, turbulence and wake-induced roll is imparted on the encountering aircraft. These axial type encounters may have an interaction with the wake flow field characterized by turbulence that is longer lasting than other types of encounters. This turbulent interaction, known as the washboard effect or nibbling, occurs when the encountering aircraft is within the wake flow field but not in the core of a wake vortex. An encountering aircraft may be expelled from the wake vortex in an axial encounter due to the rotation of the wake vortex. If an encountering aircraft continues into the core of the wake vortex, the induced roll force is usually brief in comparison to the overall interaction with the wake flow field. See Figure 16, Axial Wake Vortex Encounter. Figure 16. Axial Wake Vortex Encounter 8.3.2 Axi al encounters may cause the encountering aircraft to roll significantly in one direction and then roll in the other direction as the aircraft passes from one wake vortex to the other counter-rotating vortex. For example, an aircraft passes into the right-side wake vortex of the generating aircraft that induces a roll to the left. The pilot inputs a counter-roll force to the right. The aircraft exits the right-side wake vortex and enters the left-side wake vortex, causing the aircraft to roll to the right. In this case, the roll to the right is possibly exacerbated by the pilot control inputs from the previous vortex recovery actions. Severity may increase in this scenario as the second roll force nominally rolls the aircraft further than the first, and the pilot may overstress the aircraft with a quick control reversal. It is also possible to encounter the same wake vortex and corresponding roll direction more than once. 8.3.3 During a crossing encounter, where the aircraft crosses the wake flow field at a larger angle, turbulence may be experienced due to the vertical air movements of the wake vortices. Crossing encounters are brief due to the speed at which the encountering aircraft passes through the wake flow field. In a crossing encounter the encountering aircraft may experience turbulence that may be severe but will experience less wake-induced roll ### Page 17 13 when compared to an axial encounter. See Figure 17, Air Movement Within Wake Vortices, and Figure 18, Crossing Wake Vortex Encounter. Figure 17. Air Movement Within Wake Vortices Fi gure 18. Crossing Wake Vortex Encounter 8.4 E ncountering Aircraft Energy State. The energy state of the encountering aircraft influences the severity of the encounter. A pilot has three sources of energy available to manage or manipulate the flightpath of an aircraft. These three sources include kinetic energy (i.e., airspeed), potential energy (i.e., altitude above the ground level), and chemical energy (i.e., engine thrust). The balance of these combined energies describes the energy state of an aircraft at any given time. Refer to FAA-H-8083-3, Airplane Flying Handbook, for more information regarding aircraft energy states. ### Page 18 8.4.1 An encountering aircraft in the takeoff or approach-to-landing flight phase is at a lower energy state (e.g., low airspeed and low altitude) and may have a higher severity encounter with wake vortices than the same aircraft with a higher energy state. The time allotted for a pilot to recover from a wake vortex encounter is compressed when the aircraft is closer to terrain or obstacles. 8.4.2 An encountering aircraft that is above maneuvering speed at a high kinetic energy relative to the “envelope” of the Vg diagram is more susceptible to a pilot action that may overstress the aircraft during recovery. Rapid and large alternating control inputs, especially in combination with large changes in pitch, roll, or yaw, may result in structural failures at any speed, including below maneuvering speed. 8.5 Pilot Influence on Likelihood and Severity of a Wake Vortex Encounter. The training, knowledge, decision making, awareness, and skill of a pilot may significantly influence both the likelihood and severity of a wake vortex encounter. 9 WAKE VORTEX ENCOUNTER MITIGATIONS. Wake vortices are generally a hazard invisible to the human eye but may be detected visually during times of high humidity or when wake vortices interact with smoke or clouds. Pilots are encouraged to learn to envision the location and movements of the vortices generated by other aircraft and to adjust their flightpath accordingly to mitigate the likelihood and/or severity of a wake vortex encounter. The best risk mitigation for wake vortex encounters is avoidance. Wake mitigations for aircraft behind the flightpath of a similar or larger-sized aircraft include: 9.1 Departures. The following are recommendations for pilots in the departure phase of flight. 9.1.1 All Departures. For all departures, pilots are encouraged to: 1. Be alert for any departure situation that may lead to a wake vortex encounter. 2. Be aware of how the expected wind direction and speed along the anticipated departure path may affect wake vortices from a preceding aircraft. 3. Avoid following or crossing behind and below the flightpath of a similar or larger-sized aircraft without adequate time to allow for wake vortex decay and drift. 4. Adjust aircraft operations and flightpath as necessary to preclude serious wake vortex encounters. 5. Pace their departure, including expected departure flightpath, to give ample time and distance for wake vortex decay and drift, especially if their flightpath crosses at or below the flightpath of a similar or larger-sized aircraft or rotorcraft. 6. Avoid the flightpath of a preceding aircraft by altering their flightpath above or laterally upwind, or both, of the flightpath of the generating aircraft. ### Page 19 9.1.1.1 At controlled airports, a pilot may request additional time for wake turbulence separation. A pilot is encouraged to make this request before taxiing onto the runway. 9.1.1.2 At uncontrolled airports, including at a part-time controlled airport when the control tower is not in operation, the pilot in command (PIC) is solely responsible for wake vortex encounter avoidance and mitigation, in accordance with 14 CFR § 91.3(a). 9.1.2 Departure from the Same or Closely Spaced Parallel Runway Following a Departure. When departing after a similar or larger-sized aircraft has taken off on the same runway, or on a closely spaced parallel runway (i.e., parallel runway separated by less than 2,500 feet), where conditions exist for the wake to drift into their flightpath, pilots are encouraged to: 1. Delay operations to allow for wake decay and drift, as needed. For reference, aircraft taking off from the same runway or a parallel runway are to be separated by air traffic control (ATC) in accordance with FAA Order JO 7110.65, Air Traffic Control. For a small aircraft, prior to the issuance of a takeoff clearance, ATC requires an interval of at least 2 minutes to have elapsed since the takeoff of a Boeing 757-size aircraft and 3 minutes since the takeoff of an Airbus A380-size aircraft. ATC will not clear a small aircraft to line up and wait behind a “Heavy” or “Super” category aircraft. 2. Take note of the takeoff rotation point of the preceding aircraft as well as the departure flightpath. 3. Rotate prior to the rotation point of the preceding aircraft and continue climbing above the flightpath of the preceding aircraft or alter their flightpath upwind until above or clear of the flightpath of the preceding aircraft. 4. Avoid a flightpath that crosses below and behind the departure flightpath of the preceding aircraft. See Figure 19, Departure Flightpath. Figure 19. Departure Flightpath 9.1.3 D eparture from the Same or Closely Spaced Parallel Runway Following an Arrival. When departing after a similar or larger-sized aircraft has arrived on the same or closely spaced parallel runway, where conditions exist for wake to drift into their flightpath, pilots are encouraged to: ### Page 20 1. Take note of the landing touchdown point of the preceding aircraft. 2. Rotate after the point of touchdown of the preceding aircraft, or delay operations to allow for wake decay and drift. 3. Avoid a flightpath that crosses below and behind the descent path of the preceding aircraft. 9.1.4 Departure Following an Opposite Direction Departure from the Same or Closely Spaced Parallel Runway. When departing after a similar or larger-sized aircraft has taken off from the opposite end of the same or closely spaced runway, where conditions exist for wake vortices to drift into their flightpath, pilots are encouraged to delay operations to allow for wake decay and drift. See Figure 20, Opposite Direction Departure. Figure 20. Opposite Direction Departure 9.1.5 D eparture from a Runway Intersection. When departing from an intersection from the same runway, or from a closely spaced parallel runway with a staggered threshold, often referred to as an offset parallel runway, where conditions exist for wake to drift into their flightpath, after a similar or larger-sized aircraft has departed, pilots are encouraged to: 1. Take note of the takeoff rotation point of the preceding aircraft as well as the departure flightpath. 2. Rotate prior to the rotation point of the preceding aircraft and continue climbing above the flightpath of the preceding aircraft or alter course upwind until above or clear of the flightpath of the preceding aircraft. 3. Avoid a flightpath that crosses below and behind the departure flightpath of the preceding aircraft. See Figure 21, Intersection Departure. ### Page 21 17 Figure 21. Intersection Departure 9.1.6 De parture from a Crossing Runway Following a Departure. When departing after a similar or larger-sized aircraft has taken off from a crossing runway, pilots are encouraged to: 1. Take note of the takeoff rotation point of the preceding aircraft, the departure flightpath, and envision the drift of the wake vortices. 2. Avoid a flightpath that crosses below and behind the flightpath of the preceding aircraft. 3. Rotate and climb above the flightpath of the preceding aircraft or alter course upwind until above or clear of the flightpath of the preceding aircraft, or both. See Figure 22, Crossing Departures. Figure 22. Crossing Departures 9.1.7 De parture from a Crossing Runway Following a Landing Aircraft. When departing after a similar or larger-sized aircraft has landed on a crossing runway, pilots are encouraged to: ### Page 22 1. Take note of the point of touchdown of the preceding aircraft and the approach path, and envision the drift of the wake vortices. 2. Avoid a flightpath that crosses below and behind the preceding aircraft. 3. Rotate and climb above the flightpath of the preceding aircraft or alter course upwind until above or clear of the flightpath of the preceding aircraft, or both. 9.1.8 Departure from Converging Runways. Converging runways have various layouts and hazards. Pilots are encouraged to avoid a flightpath that crosses below and behind a similar or larger-sized aircraft. 9.1.9 Departures Following an Aircraft that Performs a Go-Around. When departing after a similar or larger-sized aircraft performs a missed approach, low approach, go-around, balked landing, or touch and go, the wake vortex hazard may exist along the runway and in your flightpath. For a small aircraft, prior to the issuance of a takeoff clearance, ATC requires an interval of at least 3 minutes to have elapsed since the takeoff of a Boeing 757-size aircraft and 4 minutes since the takeoff of an Airbus A380-size aircraft. See Figure 23, Missed Approach Wake Vortices. Figure 23. Missed Approach Wake Vortices 9.1.10 D eparture from an Adjacent Airport. When departing from an airport adjacent to another airport with a similar or larger-sized aircraft operations, pilots are encouraged to avoid wake vortices from preceding arriving and departing aircraft from both airports. See Figure 24, Departures from Adjacent Airports. Figure 24. Departures from Adjacent Airports ### Page 23 9.1.11 Departure Following Rotorcraft Operations. The effects of rotorcraft wake vortices, downwash, and outwash may be stronger than expected compared to fixed-wing aircraft of a similar size. Pilots of fixed-wing aircraft are encouraged to: 1. Regard rotorcraft of a similar size as a larger aircraft for wake vortex avoidance. 2. Avoid the area within three times the rotor diameter, of the nearest main rotor, of a rotorcraft in a hover or slow hover taxi. See Figure 25, Avoiding Rotorcraft Downwash and Outwash. 3. Avoid wake vortices from an arriving or departing rotorcraft that may be present in different locations than the expected location of wake vortices from fixed-wing aircraft. Figure 25. Avoiding Rotorcraft Downwash and Outwash 9.2 A rrivals. The following are recommendations for pilots in the departure phase of flight. 9.2.1 All Arrivals. For all arrivals, pilots are encouraged to: 1. Be alert for any arrival situation that may lead to a wake vortex encounter. ### Page 24 2. Adjust aircraft operations and flightpath as necessary to preclude serious wake vortex encounters. 3. Space the arrival, including the expected approach path of their aircraft, to give ample time and distance for wake vortex decay and drift. 4. When on approach, take note of wind speed and direction, runway threshold locations, relative glidepaths, touchdown and rotation points of similar and larger-sized aircraft. 5. Avoid following or crossing below the flightpath of a similar or larger-sized aircraft without adequate time and distance to allow for wake vortex decay and drift. 6. Avoid flying below the flightpath of a preceding aircraft by delaying operations to allow for wake decay and drift, as well as altering their flightpath above or altering their flightpath laterally upwind, or both. 7. When following a similar or larger-sized aircraft, stay at or above the electronic or visual glidepath, as appropriate. Otherwise, consider remaining at or above a nominal 3-degree glidepath using the “3 to 1” glidepath guidance. To approximate the altitude of a 3-degree glidepath, for every nautical mile (NM) away from the runway, add 300 feet above the touchdown zone elevation (TDZE) (e.g., approximately 1,500 feet above TDZE at 5 NM). Exceptions exist where a 3-degree glidepath (i.e., 318 feet per NM descent) is too low, including operations near mountainous terrain. 8. Maintain a line of sight to an aim point that is beyond the expected touchdown point of the preceding aircraft, no less than 1,000 feet from the threshold of the arrival runway. 9. Note the touchdown point of the preceding aircraft (e.g., a puff of smoke from tire contact of the preceding aircraft) and adjust the aim point as necessary. 10. Maintain the line of sight to the aim point and stay above the flightpath of the preceding aircraft to touchdown. 11. If there is any doubt as to the safety of the arrival, make the decision early to perform a missed approach, go-around, or a balked landing. 12. If a touchdown point extension due to wake vortex encounter mitigation does not allow sufficient distance to safely stop the aircraft prior to the end of the useable runway or would cause an unstabilized approach, delay the approach to landing to allow ample time and distance for wake decay and drift before landing at an appropriate touchdown point. 9.2.1.1 Visual Approaches Following Another Aircraft. Acceptance of ATC instructions to follow another aircraft, or to maintain visual separation from another aircraft, is an acknowledgment that the pilot will maneuver the aircraft as necessary to avoid the other aircraft and to maintain adequate wake turbulence separation and avoidance. In a radar environment with ATC, pilots may query ATC for updates on separation and groundspeed with respect to a preceding aircraft. ### Page 25 9.2.1.1.1 During visual approaches or at uncontrolled airports, including at a part-time controlled airport when the control tower is not in operation, or during charted visual flight procedures (CVFP), pilots are solely responsible for wake turbulence separation and avoidance. 9.2.2 Arrival Following a Landing Aircraft to the Same or Closely Spaced Parallel Runway. When arriving after a similar or larger-sized aircraft has landed on the same runway, or a closely spaced parallel runway, where conditions exist for wake to drift into their flightpath, pilots are encouraged to delay operations to allow for wake decay and drift, if required. Pilots are encouraged to approach the runway at or above the flightpath of the preceding aircraft and touchdown after the touchdown point of the preceding aircraft. See Figure 26, Landing After a Larger Aircraft. 9.2.2.1 In certain scenarios when parallel approach courses authorized for simultaneous dependent operations, parallel offset approaches, or simultaneous offset instrument approaches (SOIA) are in use, aircraft on both approaches are encouraged to remain on the electronic glidepath, as applicable, for wake vortex encounter mitigation. Refer to the instrument approach chart notes for details. Figure 26. Landing After a Larger Aircraft 9.2.3 A rrival Behind an Aircraft Landing on a Staggered Threshold. When arriving behind a similar or larger-sized aircraft landing on a closely spaced parallel runway closer than 2,500 feet, where conditions exist for wake to drift into your flightpath, with a staggered threshold, consider the implications of where the wake vortices may be found and avoid that area. Pilots are encouraged to approach the runway at or above the flightpath of the preceding aircraft and touchdown after the touchdown point of the preceding aircraft. 9.2.4 Arrival Behind an Aircraft with a Different Glidepath Angle. Aircraft abeam each other on approaches to nonstaggered parallel runways with the same glidepath angle tend to be at approximately the same altitude. Conversely, on approaches to staggered parallel runways (i.e., one TDZ is more distant) with the same glidepath angle, when aircraft are abeam each other, the aircraft on approach to the more distant TDZ tend to be relatively higher. When following a similar or larger-sized aircraft to a staggered parallel runway, where conditions exist for wake to drift into their flightpath, to the closer TDZ, pilots are ### Page 26 22 encouraged to adjust their flightpath or delay operations accordingly. See Figure 27, Parallel Runways With Threshold Stagger. Figure 27. Parallel Runways With Threshold Stagger 9.2.5 Arriva l Following a Departing Aircraft from the Same or Closely Spaced Parallel Runway. When arriving after a similar or larger-sized aircraft has departed on the same or closely spaced parallel runway, where conditions exist for wake to drift into their flightpath, pilots are encouraged to touchdown prior to the rotation point of the larger aircraft. See Figure 28, Landing After a Departing Aircraft. Figure 28. Landing After a Departing Aircraft 9.2.6 A rrival Following a Departure from a Crossing Runway. When arriving after a similar or larger-sized aircraft has departed from a crossing runway, pilots are encouraged to take note of the takeoff rotation point of the preceding aircraft, the possible wake vortex drift, as well as the departure flightpath. Pilots are encouraged to avoid a flightpath that crosses below and behind the flightpath of the preceding aircraft. If the preceding aircraft rotates prior to the intersection, pilots are encouraged to execute a missed approach or go-around unless a landing is ensured well before the intersection. See Figure 29, Landing After a Crossing Runway Departure (Rotation Point Before Intersection), and Figure 30, Landing After a Crossing Runway Departure (Rotation Point After Intersection). ### Page 27 23 Figure 29. Landing After a Crossing Runway Departure (Rotation Point Before Intersection) Figu re 30. Landing After a Crossing Runway Departure (Rotation Point After Intersection) 9.2.7 Arriv al Following an Aircraft Landing from a Converging Runway. Converging runways have various layouts and hazards. When arriving after a similar or larger-sized aircraft has landed on a converging runway, pilots are encouraged to take note of the point of touchdown of the preceding aircraft, the possible wake vortex drift, and the approach path. Pilots are encouraged to avoid a flightpath that crosses below and behind the ### Page 28 24 preceding aircraft. See Figure 31, Landing After an Arriving Aircraft on a Converging Runway. Figure 31. Landing After an Arriving Aircraft on a Converging Runway 9.2.8 A rrival Following a Landing on the Opposite End of the Runway. When arriving after a similar or larger-sized aircraft has taken off from the opposite end of the same or closely spaced runway, where conditions exist for wake to drift into their flightpath, pilots are encouraged to delay operations to allow for wake decay and drift away from the approach area and the possible missed approach flightpath. 9.2.9 Arrival Following an Aircraft that Performs a Go-Around. When arriving after a similar or larger-sized aircraft performs a missed approach, low approach, go-around, balked landing, or touch and go, the wake vortex hazard may exist along the runway and in your flightpath, including the possible missed approach course. 9.2.10 Arrival to an Adjacent Airport. When arriving at an airport adjacent to another airport with similar or larger-sized aircraft operations, pilots are encouraged to take care to avoid wake vortices from arriving and departing aircraft. See Figure 32, Arrival at an Adjacent Airport. ### Page 29 25 Figure 32. Arrival at an Adjacent Airport 9.2.11 Arriv al Following Rotorcraft Operations. The effects of rotorcraft wake vortices, downwash, and outwash may be stronger than expected compared to fixed-wing aircraft of a similar size. Pilots of fixed-wing aircraft are encouraged to: 1. Regard rotorcraft of a similar size as a larger aircraft for wake vortex avoidance. 2. Avoid the area within three times the rotor diameter, of the nearest main rotor, of a rotorcraft in a hover or slow hover taxi. 3. Avoid wake vortices from an arriving or departing rotorcraft that may be present in different locations than the expected location of wake vortices from fixed-wing aircraft. 9.3 En Route. 9.3.1 En Route Wake Encounter Scenarios. 9.3.1.1 Pilots are encouraged to be alert for wake vortices when operating behind and in the vicinity of aircraft climbing or descending through their altitude. 9.3.1.2 When VFR en route with 500-foot separation from IFR traffic, pilots are encouraged to avoid flight below and behind the flightpath of a similar or larger-sized aircraft. If a preceding aircraft is observed above on nearly the same path, whether opposing or overtaking, pilots are encouraged to adjust the flightpath of the aircraft laterally, preferably upwind. 9.3.1.3 When IFR en route with 1,000-foot separation from other IFR traffic, pilots are encouraged to be alert for wake vortices when approximately 5 to 25 miles after passing 1,000 feet below opposite-direction traffic or behind same-direction traffic. 9.3.2 En Route Wake Vortex Encounter Mitigations. If the hazard of wake vortex encounter is suspected, especially in the case of a generating aircraft defined as a category of “Heavy” or “Super,” pilots are encouraged to request a lateral offset upwind of the expected wake vortices. Lateral offsets upwind as small as the wingspan of the preceding aircraft may ### Page 30 26 move the trailing aircraft out of the immediate vicinity of a wake vortex. See Figure 33, Opposing Flightpaths. Figure 33. Opposing Flightpaths 9.3.2.1 Strategic Lateral Offset Procedure (SLOP) may be utilized where allowed by International Civil Aviation Organization (ICAO) Doc 4444, Procedures for Air Navigation Service (PANS), and national Aeronautical Information Publications (AIP) (i.e., oceanic airspace) to offset from an airway, preferably upwind. SLOP does not apply to domestic U.S. airspace. In domestic U.S. airspace, pilots are encouraged to request an amended clearance to fly a lateral offset, preferably upwind, as applicable. See Figure 34, In-Trail Flightpath. Figure 34. In-Trail Flightpath 9.3.2.2 Condensation trails, known as contrails, and wake vortices propagate, descend, and decay in the atmosphere differently. The ice particles that form in the exhaust of aircraft flying at high altitude are only to be used as a gross indication of the flightpath of a preceding aircraft, not the specific wake vortex location. 9.4 Wake Vortex Encounter Mitigations for Generating Aircraft. 9.4.1 Vertical Course. Large aircraft operators are encouraged to make every attempt to fly their aircraft predictably. In the terminal environment, this includes flying on the glidepath, not above it. Flying the glidepath where appropriate establishes a baseline from ### Page 31 27 which pilots of in-trail aircraft may make effective flightpath adjustments to mitigate wake vortex encounters. At airports without visual or electronic glidepath indications, or both, pilots are encouraged to use a 3-degree glidepath using the “3 to 1” glidepath guidance. For every NM away from the runway, the pilot is encouraged to be an additional 300 feet above the TDZE (e.g., 1,500 feet above TDZE at 5 NM). Exceptions exist where a 3-degree glidepath is too low, including operations near mountainous terrain. 9.4.2 Lateral Course. Larger aircraft operators are encouraged to remain as close to as feasible the centerline of an airway and to fly as closely as possible to the approach centerline or the extended runway centerline. Flying the lateral course predictably allows pilots of in-trail aircraft to make effective flightpath adjustments to mitigate wake vortex encounters. 9.4.3 Radio Phraseology. Pilots of “Heavy” or “Super” wake turbulence category aircraft are encouraged to use the appropriately designated weight identifying term in radio communication. 9.5 Wake Vortex Encounter Mitigations Utilized by ATC. 9.5.1 Wake Vortex Encounter Mitigation Roles and Responsibilities. In accordance with 14 CFR § 91.3(a), the PIC of an aircraft is directly responsible for, and is the final authority as to, the operation of that aircraft. This responsibility includes wake vortex encounter avoidance and mitigation. Pilots arriving and departing from uncontrolled airports, or accepting a clearance for a visual approach, operating using VFR outside of controlled airspace are accepting the responsibility for wake vortex encounter avoidance and mitigation. Per Order JO 7110.65, when 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. 9.5.2 Wake Assessment. Wake assessment performed by the FAA defines the characteristics of an aircraft wake vortices, including the initial wake strength and the wake age required to reduce the residual wake strength encountered by a following aircraft. Wake assessment also quantifies the ability of a following aircraft to encounter wake vortices. 9.5.3 Wake Categorization. Wake assessments result in wake categorization of an aircraft to define separation standards in time or distance between leader and follower aircraft pairs to be used by ATC. For example, on an approach, ATC may separate a “Heavy” category follower aircraft behind another “Heavy” category leader aircraft by the Minimum Radar Separation (MRS). If, instead, the follower aircraft was a “Light” category aircraft behind a “Heavy” category aircraft, the controller would increase the separation allowing for the wake vortices to decay and move away from the flightpath. Originally, wake categorization and minimum separation standards were based on the maximum gross takeoff weight of an aircraft. In this weight-only wake categorization of aircraft there is potential for aircraft with similar weights to have markedly different wake generation and behavior characteristics, as well as differing abilities to encounter wake as a following ### Page 32 28 aircraft. Weight-only categorization, therefore, carries heightened safety risks or less efficient use of congested airspace. Advances in the understanding of wake behavior and computational simulations facilitated the development of Wake Turbulence Recategorization (RECAT). RECAT offered a multiparameter aircraft classification system that enhanced safety over the weight-only structure while yielding operational efficiency gains. RECAT was modified into different versions including RECAT 1.5 and RECAT II. Now, Consolidated Wake Turbulence (CWT) takes advantage of the continuing evolution of wake mitigation strategies to consolidate the benefits of previous RECAT efforts. ATC facilities are currently transitioning to CWT separation standards. 9.5.3.1 CWT categorizes aircraft into nine separate categories, labeled A through I. “A” is the category designator for a “Super” (e.g., Airbus A380), and “I” is the category designator for a smaller aircraft (e.g., Beechcraft King Air 200). 9.5.3.2 ICAO Wake Turbulence Category (WTC) is based on weight only. The designators are “L” for “Light” category aircraft with a maximum certificated takeoff weight of 15,400 pounds or less. “M” for “Medium” category aircraft with a maximum certificated takeoff weight of more than 15,400 pounds to 300,000 pounds. “H” for “Heavy” category aircraft with a maximum certificated takeoff weight of more than 300,000 pounds. There is also a designator “J”, which denotes a “Super” category aircraft type (e.g., Airbus A380). 9.5.4 Flight Plan. An ICAO compliant flight plan such as FAA Form 7233-4, Pre-Flight Pilot Checklist and International Flight Plan, requires the input of an aircraft type designator of an aircraft as well as the ICAO WTC in Item 9 of FAA Form 7233-4. The aircraft type designators, ICAO WTCs, and the corresponding CWT category for an aircraft type can be found in the current version of Order JO 7360.1. 9.5.4.1 Automation in the ATC system automatically adjusts the wake separation category if the aircraft flight plan is filed correctly with the aircraft type designator found in Order JO 7360.1. 9.5.4.2 It is important that the standard abbreviation for an aircraft type designator is listed correctly in the flight plan. ATC automation systems will not present the correct information to the controller unless the current and proper aircraft type is listed in the flight plan. For example, an Eclipse 550 jet is listed as an EA50; if the operator listed E550, the automation system would recognize the aircraft as an Embraer Legacy that is in a different CWT category. 9.5.4.3 Operators of aircraft without an assigned aircraft type designator are to enter “ZZZZ” as the aircraft type designator in their flight plan. If an operator, or controller, enters a “ZZZZ” designator into the flight plan, or the aircraft type designator entered has not been assessed for wake separation standards, the ATC automation presents the controller with a no weight (NOWGT) classification. The NOWGT classification is better described as “no wake ### Page 33 29 assessment.” NOWGT aircraft are given added separation that may affect the efficiency of airspace use both in front of and behind the NOWGT aircraft. 9.5.5 Wake Turbulence Cautionary Advisories. Wake turbulence cautionary advisories are issued when, in the opinion of the controller, wake turbulence may have an adverse effect on traffic. When traffic is known to be a “Super” or “Heavy” category aircraft, ATC will include the word “Super” or “Heavy” in the description. ATC issues wake turbulence cautionary advisories that include the position, altitude (if known), direction of flight, and the phrase “Caution, Wake Turbulence” to aircraft operating behind an aircraft that requires wake turbulence separation. Wake turbulence cautionary advisories are issued to VFR aircraft not being radar vectored that are behind the larger aircraft, VFR arriving aircraft that have previously been radar vectored and the vectoring has been discontinued, and IFR aircraft accepting a visual approach or visual separation. Note: Whether or not a warning or information has been given, the pilot is encouraged to adjust aircraft operations and flightpath as necessary to preclude wake vortex encounters. 9.5.6 ATC Inquiry. When any doubt exists about maintaining safe separation distances between aircraft to avoid wake turbulence, pilots are encouraged to ask ATC for updates on separation distance, groundspeed, and altitude. 10 WAKE VORTEX ENCOUNTER RECOVERY GUIDANCE. A wake vortex encounter does not always result in an unsafe condition. Depending on many variables discussed in this AC, a severe wake vortex encounter may include an undesired aircraft state, aircraft upset, or possibly a LOC-I aircraft accident. Incident and accident history has found that pilot inputs during a wake vortex encounter may have a positive or a negative effect. Refer to the Aircraft Flight Manual (AFM) or company policies, or both, for aircraft-specific upset recovery procedures. 10.1 Situational Awareness. The goal of situational awareness, as it relates to wake vortices, is avoidance. Furthermore, if a pilot is situationally aware and yet experiences a wake vortex encounter, the goal is to mitigate the encounter by recognizing and escaping (e.g., initiating a go-around/balked landing/missed approach when encountering a wake vortex on approach). If an aircraft encounters a severe wake vortex that causes an undesired aircraft state or aircraft upset, the goal of situational awareness is to understand the aircraft state in relation to the AOA, the load factor, the horizon, and energy state, including kinetic energy, potential energy, and chemical energy, so that the pilot will make the correct inputs to recover effectively. Understanding the situation that an aircraft is in is crucial for effectively initiating recovery procedures. A pilot who is aware of the energy state and flightpath of the aircraft is less likely to be startled and, therefore, more likely to deal with a wake vortex encounter with the proper control inputs versus rapid reactive responses and reversals. The larger the excursion from normal flight, the more challenging an upset recovery becomes. Attitude instruments may be unreliable depending on the capabilities of the attitude instrument and the amount of roll and pitch experienced in the aircraft upset. Pilots are encouraged to use all available resources, including looking outside the flight deck windows, including side windows for extreme ### Page 34 30 pitch angles, for attitude information. Failing to reference external cues or inadequately cross-checking instruments (e.g., neglecting to monitor all the instruments or fixating on certain instrument indications and not detecting changes in others) may exacerbate an aircraft upset. Regaining and then maintaining control of the aircraft is paramount. 10.2 Startle and Surprise. The expectations of an unprepared pilot may be violated when exposed to a sudden, intense event that may happen in a wake vortex encounter and may produce a startle effect (e.g., automatic muscle reflex, raised heart rate, cognitive impairment, etc.). A surprise that violates a pilot’s expectations can affect the mental processes used to respond to the event. Startle and surprise may cause the pilot to input inappropriate controls that overshoot the desired response. An inappropriate response to a wake vortex encounter that leads to an aircraft upset may lead to another aircraft upset in a different direction or axis. A pilot who is aware of the energy state and flightpath is less likely to be startled and, therefore, more likely to deal with the situation with controlled inputs versus reactive responses. 10.3 Flight Control Inputs. Control inputs that are appropriate at one point in the flight envelope might not be appropriate in another part of the flight envelope. Pilots are encouraged to have a fundamental understanding of flight dynamics to correctly determine the control inputs necessary for recovery. Aircraft upsets caused by a wake vortex encounter may involve a rapid roll reversal as the aircraft transitions across one wake vortex that induces a roll in one direction and then enters the other wake vortex that induces a roll in the opposite direction. Pilots are encouraged to exercise caution with control inputs and ensure that control input is proportional to the situation, including the flight envelope, unless ground contact is imminent. It may be advisable, and if conditions permit, to allow the aircraft to transition through the wake vortex and then recover from any resultant undesired aircraft state versus aggressively trying to control the aircraft during the wake encounter. A pilot-induced oscillation (PIO) may occur when a pilot’s commands become out of phase with the aircraft motion. A PIO may be initiated during an upset recovery if a pilot reacts with large rapid inputs before determining what is occurring. Precedents exist for wake vortex encounter events in which the pilot inputs exacerbated the undesired aircraft state caused by the wake vortex encounter. 10.3.1 Pitch. Aircraft upset may lead to an aircraft at or close to the critical AOA and stall. An airplane wing may stall in any attitude and at any airspeed. The elevator controls the load factor of the aircraft. “Load factor” is the measure of the acceleration being experienced by the aircraft also known as “G” loading. Higher load factors increase the AOA and reduce flight control effectiveness compared to an aircraft at 1G or less than 1G. Zero or negative G’s may have detrimental effects on the aircraft and occupants within. A priority in recovery from an aircraft upset is to manage the AOA and load factor to recover from or prevent a stall and return the aircraft to a desired aircraft state without overstressing the aircraft. Pilots are encouraged to manage the load factor to recover from an upset effectively without stalling or overstressing the aircraft. The use of actions affecting pitch (e.g., elevator input, pitch trim activation) may aggravate the upset situation or may result in high structural loads. ### Page 35 10.3.2 Roll. An increasing bank results in a reorientation of the lift vector from the vertical, which, in turn, creates a horizontal lift component and a reduced vertical lift component. When combined with an increased pitch input, an increase in the bank creates an increased load factor. At any speed, large aggressive control deflection reversals may lead to a load factor that exceeds structural design limits. 10.3.3 Yaw. A yaw input is not the preferred initial response to a wake vortex encounter. Pilots are encouraged to use yaw input in combination with roll inputs to eliminate sideslip, not to create sideslip or counter wake-induced roll. Prior experience and training that emphasized the use of yaw input to maneuver in roll may not apply to all aircraft operations. Using yaw to counter roll rate during a roll upset may lead to an undesirable aircraft response. Pilot overreaction in yaw may induce abrupt yawing moments and violent out-of-phase roll rates, which may lead to successive cyclic rudder deflections, known as rudder reversals, as the pilot tries to control the resulting motions. In past aircraft accidents, it was determined that the accident was the result of the in-flight separation of the vertical stabilizer and subsequent loss of control due to excessive rudder pedal inputs in response to a wake vortex encounter. 10.3.4 Thrust. Increased chemical energy (i.e., increased thrust) may be used to increase kinetic energy, increase potential energy, or both. Some aircraft produce a thrust vector that is not coincident with the longitudinal axis of the aircraft and may produce a pitch up or down movement that may not be desired. Propeller-driven aircraft have a faster thrust buildup compared to jet engines that have a longer spool-up time. Propeller effects, however, may introduce rolling moments and unwanted slip or skid in response to power changes that require pilot compensation. 10.3.5 Lift or Drag Devices. The aircraft’s energy state and trend need to be assessed prior to the deployment or retraction of lift or drag, or both, devices (e.g., flaps, slats, spoilers/speedbrakes). 10.3.6 Autoflight System. Refer to the AFM for specific guidance on the autoflight system, including autothrust systems and yaw damper controls. During a wake vortex encounter, if conditions permit, the autoflight system is engaged and remains engaged, and the aircraft is not in an undesired state, it may be appropriate to allow the autoflight system to fly the transition through the wake vortex, rather than aggressively trying to manually control the aircraft during the wake encounter. An autoflight system may disconnect unexpectedly because of excessive roll or pitch rates, roll or pitch angles, control surface deflection rates, or forces that are not normal. Approaching the limits of an autoflight system may mask the actual airplane trim state, as well as resultant changes in performance and handling qualities. Pilots are encouraged to be prepared to assume manual control of the aircraft if the autoflight system disconnects or if the aircraft attains an undesired state or upset. If the aircraft progresses into an upset, in coordination with AFM procedures, a pilot is encouraged to disconnect the autoflight systems, including the autothrust to recover. 10.4 Other Upset Recovery Considerations. The routine and/or mandatory use of autoflight systems during high-altitude operations often results in pilots having less experience with ### Page 36 32 manual flight control in this environment. However, if a wake vortex is encountered at high altitude, pilots generally have more time to recover due to the greater altitude available. In such scenarios, methodical and deliberate flight control inputs are crucial, as opposed to hasty or arbitrary reactions. In situations such as low-altitude operations, depending on the severity of the wake encounter, the time allowance is shortened for the pilot to recognize the encounter, identify the resultant forces, and make an effective recovery. Proper situational awareness is paramount to upset recovery. When an encountering aircraft transits a wake vortex low to the ground (i.e., low potential energy), relatively slow (i.e., low kinetic energy), and at a higher AOA than would occur during takeoff or landing, the situation may be critical. Prevention and avoidance of wake vortices is always the goal, but if the pilot recognizes that their aircraft is beginning to encounter wake vortices, evasive actions are to be enacted to prevent aircraft upset. 11 PILOT WAKE VORTEX ENCOUNTER REPORTING. Wake vortex encounter reporting is an important aspect of ensuring current aircraft wake separation standards and guidance are effective. Only a pilot knows that they have had a wake vortex encounter. If a pilot believes they have had a wake vortex encounter, they are encouraged to report the event. When reporting, pilots are encouraged to be as specific as possible, including details such as location, altitude, aircraft configuration, phase of flight, roll rate, maximum bank angle, changes to altitude and airspeed, etc. 11.1 Reporting to ATC. When in contact with ATC, pilots are encouraged to report all suspected wake vortex encounters as soon as practical to ATC. When uncontrolled by ATC, pilots may call ATC by radio or telephone to report a wake vortex encounter. When reporting a wake vortex encounter, pilots are encouraged to take care to distinguish between a wake vortex encounter and atmospheric turbulence. Pilot reports of aircraft wake vortex encounters received through ATC are recorded as a Mandatory Occurrence Report (MOR) per FAA Order JO 7210.632, Air Traffic Organization (ATO) Occurrence Reporting. 11.2 Aviation Safety Reporting System (ASRS). Pilots are encouraged to utilize the National Aeronautics and Space Administration (NASA) ASRS to report wake vortex encounters. A pilot may file ASRS reports by visiting the NASA Ames Research Center website at https://asrs.arc.nasa.gov/. 11.2.1 Data Anonymity. Pilot reports of wake vortex encounters through the NASA ASRS system are de-identified. All personal and organizational names are removed. Dates, times, and related information, which could be used to infer an identity, are either generalized or eliminated. As a part of the NASA Ames research system, quarterly reports of wake vortex encounters are supplied to the FAA. These reports document event dynamics and contributing factors underlying each reported wake vortex encounter. A sampling of the factors to be analyzed include the assessed magnitude of the wake encounter, aircraft spacing, aircraft type, runway configuration, and consequences of the encounter. ### Page 37 11.3 Operator Reporting Policies. Air carriers and operators may have policies regarding how to report wake vortex encounters, including Aviation Safety Action Programs (ASAP), Aircraft Communications Addressing and Reporting System (ACARS), or other records used by that operator, such as a captain’s report. 11.4 FAA Hotline. The FAA Hotline accepts reports related to the safety of the National Airspace System (NAS), violations of 14 CFR, aviation safety issues, and reports related to FAA employees or FAA facilities. The FAA Hotline provides a single venue for FAA employees, the aviation community, and the public to file their reports. Visit the FAA Hotline web page at https://www.faa.gov/about/office_org/headquarters_offices/aae/prog rams_services/faa_hotlines. 11.5 Notification of Aircraft Accidents or Incidents. If an accident or incident occurs, pilots are encouraged to remain in compliance with the reporting requirements of 49 CFR part 830. ### Page 38 Appendix A A-1 APPENDIX A. ADMINISTRATIVE INFORMATION A.1 Advisory Circular (AC) Feedback Form. For your convenience, the AC Feedback Form is the last page of this AC. Note any deficiencies found, clarifications needed, or suggested improvements regarding the contents of this AC on the Feedback Form. A.2 Related Publications. A.2.1 ACs. The current editions of each of the following ACs can be found at https://www.faa.gov/regulations_policies/advisory_circulars/ and in the Dynamic Regulatory System (DRS) at https://drs.faa.gov. • AC 91-79, Aircraft Landing Performance and Runway Excursion Mitigation. • AC 120-88, Preventing Injuries Caused by Turbulence. • AC 120-109, Stall Prevention and Recovery Training. • AC 120-111, Upset Prevention and Recovery Training. • AC 120-123, Flightpath Management. A.2.2 Orders. You can find current and historical FAA orders at https://www.faa.gov/regulations_policies/orders_notices/ and in DRS at https://drs.faa.gov under “Air Traffic Organization (ATO),” “Air Traffic Plans and Publications.” • FAA Order JO 7110.65, Air Traffic Control. • FAA Order JO 7110.126, Consolidated Wake Turbulence (CWT). • FAA Order JO 7110.308, Simultaneous Dependent Approaches to Closely Spaced Parallel Runways. • FAA Order JO 7360.1, Aircraft Type Designators. A.2.3 International Civil Aviation Organization (ICAO) Guidance. ICAO Doc 4444, Procedures for Air Navigation Service (PANS). A.2.4 Other Related References. • Wake Turbulence Training Aid: https://www.faa.gov/training_testing/training/wake. • Airplane Upset Prevention and Recovery Training Aid: https://www.faa.gov/pilots/tra ining. • FAA-H-8083-3, Airplane Flying Handbook. • Pilot Guide to Takeoff Safety: https://www.faa.gov/sites/faa.gov/files/other_visit/avia tion_industry/airline_operators/training/takeoff_safety.pdf. ### Page 39 Appendix A A-2 A.3 Abbreviations and Acronyms. Acronym Term AC Advisory Circular ACARS Aircraft Communications Addressing and Reporting System AFM Aircraft Flight Manual AIM Aeronautical Information Manual AIP Aeronautical Information Publication AOA Angle of Attack ASAP Aviation Safety Action Program ASRS Aviation Safety Reporting System ATC Air Traffic Control ATO Air Traffic Organization AURTA Airplane Upset Recovery Training Aid CFR Code of Federal Regulations Contrails Condensation Trails CVFP Charted Visual Flight Procedures CWT Consolidated Wake Turbulence DRS Dynamic Regulatory System FAA Federal Aviation Administration ICAO International Civil Aviation Organization IFR Instrument Flight Rules LOC-I Loss of Control In Flight MOR Mandatory Occurrence Report MRS Minimum Radar Separation NAS National Airspace System NASA National Aeronautics and Space Administration NM Nautical Mile NOWGT No Weight PIO Pilot-Induced Oscillation RBDM Risk-Based Decision Making RECAT Wake Turbulence Recategorization ### Page 40 Appendix A A-3 Acronym Term SOIA Simultaneous Offset Instrument Approach SLOP Strategic Lateral Offset Procedure SRS Same Runway Separation TDZ Touchdown Zone TDZE Touchdown Zone Elevation WTC Wake Turbulence Category WTMA Wake Turbulence Mitigation for Arrivals WTMD Wake Turbulence Mitigation for Departures VFR Visual Flight Rules ### Page 41 Appendix B B-1 APPENDIX B. MISCELLANEOUS ATC WAKE SEPARATION EFFORTS B.1 Same Runway Separation (SRS). SRS, per FAA Order JO 7110.65, Air Traffic Control, separates aircraft taking off from the same or a parallel runway separated by less than 2,500 feet. Air traffic control (ATC) will not issue clearances that imply or indicate approval of rolling takeoffs by “Super” or “Heavy” aircraft or clear a small aircraft to line up and wait on the same runway behind a departing “Super” or “Heavy” aircraft to apply the necessary intervals. ATC categorizes aircraft in this scenario into 3 categories. As specified in Order JO 7110.65, Paragraph 3-9-6, Same Runway Separation, SRS Category I is single-engine propeller driven aircraft weighing 12,500 pounds or less, and all helicopters. Category II is twin-engine propeller driven aircraft weighing 12,500 pounds or less. Category III is all other aircraft. B.2 Intersecting Runway/Intersecting Flightpath Operations. If flightpaths are expected to cross, ATC will separate aircraft taking off behind a departing or landing aircraft on an intersecting runway. An example of separation required is 2 minutes behind a “Heavy” category aircraft, and 3 minutes behind a “Super” category aircraft. B.3 Converging Runway Operations. An operation is classified as an intersecting runway operation if the extended centerline of a runway intersects either a converging runway or the extended centerline of a converging runway within 1 nautical mile (NM), or less, from either departure end. Some exceptions do apply. B.4 Adjacent Airport Operations. At adjacent airports, ATC will ensure separation between arriving or departing instrument flight rules (IFR) aircraft and any aircraft requiring wake turbulence separation whose flightpaths intersect. For example, the required separation is 2 minutes behind a “Heavy” category aircraft, and 3 minutes behind a “Super” category aircraft. B.5 Non-Radar Interval Minima. In a nonradar environment, ATC ensures aircraft separation by using time intervals or the passage of known waypoints to maintain safe distances. For example, the required separation interval behind a “Heavy” category aircraft is 3 minutes or 6 miles and 4 minutes or 8 miles if behind a “Super” category aircraft. B.6 Wake Turbulence Mitigations for Arrivals (WTMA) Simultaneous Dependent Approaches. Per FAA Order JO 7110.308, Simultaneous Dependent Approaches to Closely Spaced Parallel Runways, certain airports with runways that are separated by 2,500 feet or less are authorized to conduct simultaneous dependent approaches. Simultaneous approaches mean that two or more parallel runways may have approaches occurring at the same time. Dependent approaches are approaches where there is a relationship between the timing of the parallel approaches. In this context, it means that diagonal spacing is required between pairs of aircraft on separate approaches, consisting of a lead aircraft and a trailing aircraft. Order JO 7110.308 further requires specific conditions to be met, such as staggered runway thresholds that create vertical differences between approaches, or adjustments to glidepath angles to establish vertical separation, or both. ### Page 42 Appendix B B-2 B.7 Wake Turbulence Mitigation for Departures (WTMD). Departures from the upwind (WTMD-enabled) runway of the designated parallel runway pairs are allowed without wake turbulence separation when the appropriate meteorological conditions exist. ### Page 43 Directive Feedback Information If you find an error in this Advisory Circular, have recommendations for improving it, or have suggestions for new items/subjects to be added, you may let us know by emailing this form to the Flight Technologies and Procedures Division at 9-AWA-AFS400-Coord@faa.gov or the Flight Standards Directives Management Officer at 9-AWA-AFB-120-Directives@faa.gov. Subject: AC 90-23H, Aircraft Wake Vortex Encounter Risk Mitigation To: Directive Management Officer, AFB-120 Directives Mailbox (9-AWA-AFB-120-Directives@faa.gov) (Please mark all appropriate line items) An e rror (procedural or typographical) has been noted in paragraph _____________ on page _______________ . Recommend paragraph _______________ on page _________ be changed as follows: (attached separate sheet if necessary) In a future change to this order, please include coverage on the following subject: (briefly describe what you want added) Other comments: I would like to discuss the above. Please contact me. Submitted by: ___________________________________________ Date: _________________ Telephone Number: _____________________________ Routing Symbol: _________________ FAA 1320-19 (11/23) Supersedes Previous Edition --- From OpenAirDocs.org, an independent open copy of FAA data. Only the Federal Register edition on govinfo.gov is the official legal text of an AD.