Wake Turbulence Brochure Cover
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Federal Aviation Administration
CAUTION Wake Turbulence

Wake Turbulence - The Problem
All Pilots are taught to be aware of wake turbulence. However, recent incidents indicate that pilots need to keep in mind how severe wake turbulence can be. In any event, wake turbulence is still out there and it can put a pilot and the aircraft at risk. This page was prepared as a reminder to pilots, to make them aware of wake turbulence and how to best avoid it.
Remember, the best defense against wake turbulence is to know and avoid areas where it occurs.

What is Wake Turbulence
All Aircraft produce wake turbulence. Wake vortices are formed any time an airfoil is producing lift. Lift is generated by the creation of a pressure differential over the wing surfaces. The lowest pressure occurs over the upper surface and the highest pressure under the wing. This pressure differential triggers the rollup of the airflow aft of the wing resulting in swirling air masses trailing downstream of the wingtips. Viewed from behind the generating aircraft, the left vortex rotates clockwise and the right vortex rotates counterclockwise.

Wingtip VorticesThe intensity or strength of the vortex is primarily a function of aircraft weight and configuration (flap setting etc.). The strongest vortices are produced by heavy aircraft, flying slowly, in a clean configuration. For example, a large or heavy aircraft that must reduce its speed to 250 knots below 10,000 feet and is flying in a clean configuration while descending, produces very strong wake. Extra caution is needed when flying below and behind such aircraft.

Induced Roll - The Greatest Hazard
While there have been rare instances where wake turbulence caused structural damage, the greatest hazard is induced roll and yaw. This is especially dangerous during takeoff and landing when there is little altitude for recovery.

Short wing span aircraft are most susceptible to wake turbulence. The wake turbulence-induced roll rates can be extreme. Countering roll rates may be difficult or impossible even in a high performance aircraft with excellent roll control authority.

Parallel or crossing Runways - Stay Heads Up for the Wake
During takeoff and landing, the vortices sink toward the ground and move laterally away from the runway when the wind is calm. A 3 to 5 knot crosswind Heads up for wake will tend to keep the upwind vortex in the runway area and may cause the downwind vortex to drift toward another runway.

At altitude, vortices sink at a rate of 300 to 500 feet per minute and stabilize about 500 to 900 feet below the flight level of the generating aircraft.

Helicopter Wake
Helicopter VorticesHelicopters also produce wake turbulence. Helicopter wakes may be of significantly greater strength than those from a fixed wing aircraft of the same weight. The strongest wake can occur when the helicopter is operating at lower speeds (20 - 50 knots). Some mid-size or executive class helicopters produce wake as strong as that of heavier helicopters This is because two blade main rotor systems, typical of lighter helicopters, produce stronger wake than rotor systems with more blades.

Stay On or Above Leader's Glide Path
Incident data shows that the greatest potential for a wake vortex incident occurs when a light aircraft is turning from base to final behind a heavy aircraft flying a straight-in approach. Above Leaders Glide Path Use extreme caution to intercept final above or well behind the heavier aircraft. When a visual approach is issued and accepted to visually follow a preceding aircraft, the pilot is required to establish a safe landing interval behind the aircraft s/he was instructed to follow. The pilot is responsible for wake turbulence separation. Pilots must not decrease the separation that existed when the visual approach was issued unless they can remain on or above the flight path of the preceding aircraft.

Warning Signs
Any uncommanded aircraft movements (i.e., wing rocking) may be caused by wake. This is why maintaining situational awareness is so critical. Ordinary turbulence is not unusual, particularly in the approach phase. A pilot who suspects wake turbulence is affecting his or her aircraft should get away from the wake, execute a missed approach or go-around and be prepared for a stronger wake encounter. The onset of wake can be insidious and even surprisingly gentle. There have been serious accidents where pilots have attempted to salvage a landing after encountering moderate wake only to encounter severe wake vortices. Pilots should not depend on any aerodynamic warning, but if the onset of wake is occurring, immediate evasive action is a MUST!

How to Avoid Wake Turbulence
  1. Takeoff
  2. If you think wake turbulence from the preceding aircraft may be a factor, wait at least 2 or 3 minutes before taking off. (See AIM para. 7-58 b & c). Before taking the runway, tell the tower that you want to wait. Plan your takeoff to liftoff before the rotation point of the preceding aircraft.

  3. Climb
  4. If you can, climb above the preceding aircraft's flight path. If you can't out climb it, deviate slightly upwind, and climb parallel to the preceding aircraft's course. Avoid headings that cause you to cross behind and below the preceding aircraft.

  5. Crossing
  6. If you must cross behind the preceding aircraft, try to cross above its flight path or (terrain permitting) at least 1,000 feet below.

  7. Following
  8. Stay either on or above the preceding aircraft's flight path, upwind, or at least 1,000 feet below.

  9. Approach
  10. Maintain a position on or above the preceding aircraft's flight path with adequate lateral separation.

  11. Landing
  12. Ensure that your touchdown point is beyond the preceding aircraft's touchdown point, or land well before a departing aircraft's rotation point.

  13. Crossing Approaches
  14. When landing behind another aircraft on crossing approaches, cross above the other aircraft's flight path.

  15. Crosswinds
  16. Remember crosswinds may affect the position of the vortices. Adjust takeoff and landing points accordingly.

  17. Helicopters
  18. Helicopter wake vortices may be of significantly greater strength than fixed wing aircraft of the same weight. Avoid flying beneath the flight paths of helicopters.

Tell Your Story to ASRS
You can help support an FAA effort to make a safe system even safer.

If you have recently experienced wake turbulence, tell the Aviation Safe Reporting System (ASRS) about it. The ASRS is one of the ways the industry learns about safety issues. You can also help support an FAA effort to reduce the frequency and danger of wake vortex events.

Report participation is voluntary and all identifying information will be removed before the ASRS research data are given to the FAA. You can report a wake turbulence incident to the ASRS by completing a NASA/ASRS form obtained from your company, a Flight Service Station, or directly from NASA. Write to NASA/ASRS at 625 Ellis Street, Suite 305, Mountain View, California 94043, phone (415) 969-3969 or fax (415) 967-4170.

The people at ASRS may call you and request to interview you about the wake vortex incident. Participation in the callback program is also voluntary, and confidential Your information will help improve the safe of the National Airspace System.

"It felt as though we had hit a twenty-foot thick concrete wall."
Statement from a corporate pilot after hitting the wake
from a large aircraft in a slow descent across his flight path.

"We were cleared for a visual approach to the right runway and to maintain visual separation on a wide-body cleared to land on the left. Our yaw damper was MEL'ed inoperative and the aircraft kind of wallowed in the landing configuration. At 2,200 feet MSL. on about a 7 mile final, the aircraft began an abrupt roll to the left and the nose pitched down. Full scale deflection of the yoke to the right did not arrest the left roll and for a moment, it appeared the aircraft was going to roll over onto its back. Suddenly, the aircraft began to recover as the ailerons regained effectiveness. The rest of the approach and landing were normal. The winds were from the left and must have caused the wake vortices from the wide-body to drift toward the right runway final."
Statement from pilot flying a regional turboprop.

"While holding for an IFR release, a large military transport was cleared for a low approach and to remain in the pattern. Approximately 2 to 3 minutes later, I was cleared for takeoff. After takeoff, I cleaned the aircraft up and climbed about 20 knots faster than normal. Going through 1,200 feet MSL, I lowered the nose slightly because I thought I had cleared the crosswind path of the military transport. About that time, the aircraft began a smooth roll to the left and felt like it was trying to pitch up. I applied nose down pressure and then heard the engines cavitate and we pitched down rather abruptly. The aircraft then felt solid, so I throttled back and gradually pulled up and resumed the climb. The incident shook up some of the passengers, so I explained to them what I thought had happened and that I was going to return to the airport. In all my years of flying, this is the first time I have encountered the wake from a large aircraft."
Statement from a light transport pilot.

The above are actual excerpts from reports to the Aviation Safety Report System (ASRS).

For Additional Information
Order the free Advisory Circular, AC-90-23E from:

DOT, M-443.2
General Services Section
Washington, D.C. 20590

A self addressed mailing label will speed processing and delivery

A wake turbulence Training Aid has been developed by the FAA and industry. The training aid includes a report, a videotape, and a CD-ROM. Copies of the training aid are available for a fee from:

National Technical Information Service
U.S. Department of Commerce
5285 Port Royal Road
Springfield, VA 22161

or call: 703.487.4650. Request the following NTIS Accession Numbers:

Also, there is a section on wake turbulence in the current Aeronautical Information Manual (AIM).

To receive a printed copy of publication No: ASY-20 95/003
"CAUTION Wake Turbulence" brochure from which these pages are based, write:

400 7th Street, S.W.
Washington, D.C. 20590

You may also leave your request with an automated telephone answering service by dialing: (202) 267-7770