Aircraft Wake Turbulence (AC 90-23G)
Advisory Circular 90-23G provides guidance on avoiding wake turbulence from large aircraft. It explains how wake vortices are generated, their behavior (descent, outward drift, persistence), and pilot techniques for avoiding wake encounters during takeoff, landing, and enroute flight.
Why This Document Matters
Wake turbulence is an invisible killer in aviation, and this AC explains the aerodynamics behind it and how to avoid it. Wake vortices are generated by every aircraft producing lift, but large, heavy aircraft at slow speeds and clean configuration produce the most dangerous wakes. The vortices descend at about 400-500 feet per minute and drift laterally with the wind. This is heavily tested on knowledge exams and is critical practical knowledge when operating near airports that serve large aircraft.
Chapter-by-Chapter Guide
What each section covers and the key topics to study
1Wake Vortex Generation and Behavior
How wake vortices are created, their strength factors, descent rate, and dissipation characteristics.
Wake Vortex Generation and Behavior
How wake vortices are created, their strength factors, descent rate, and dissipation characteristics.
Key Topics
2Avoidance Procedures
Specific procedures for avoiding wake turbulence during takeoff, landing, and enroute operations.
Avoidance Procedures
Specific procedures for avoiding wake turbulence during takeoff, landing, and enroute operations.
Key Topics
Study Tips
- Memorize the key wake turbulence avoidance rules: when landing behind a large aircraft, stay at or above the large aircraft's glidepath and land beyond its touchdown point.
- Understand that wake vortices are worst when the generating aircraft is heavy, clean (no flaps), and slow — this is typically on approach or departure.
- Know how crosswind affects wake vortices: a light crosswind (5 knots) can keep the upwind vortex on the runway while moving the downwind vortex away. No wind means both vortices stay near the runway.
Frequently Asked Questions
How long do wake vortices last?
Wake vortices can persist for up to 3 minutes in calm wind conditions. They begin to dissipate when they contact the ground or are broken up by wind. A crosswind of 5 knots or more is generally sufficient to move vortices away from the runway.
When are wake vortices most dangerous?
Wake vortices are most dangerous when following a large, heavy aircraft that is in a clean configuration (no flaps) at slow speed — typically during approach or departure. Light aircraft are most vulnerable due to their lower wing loading.
Quick Facts
- Document ID
- AC 90-23G
- Last Updated
- 2014
- Cost
- Free
- Publisher
- FAA
Applies To
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Aircraft Wake Turbulence (AC 90-23G) is an official FAA publication available at FAA.gov
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