Insights & News

Wake turbulence in aviation: Definition and understanding

Published Friday, May 16, 2025

Wake turbulence is a critical safety hazard in aviation, created by the wingtip vortices that form behind an aircraft as it generates lift. The strength and persistence of these vortices depend on factors such as aircraft weight, wingspan, speed, and configuration. Wake turbulence poses the greatest risk to following aircraft during the takeoff and landing phases, potentially causing loss of control, sudden altitude changes, or structural stress. To mitigate these risks, pilots and air traffic controllers employ a range of avoidance strategies, separation standards, and emerging technologies.

Summary:

1. What is wake turbulence?
2. Wake turbulence hazards
3. Wake turbulence avoidance strategies
4. Air traffic control and wake turbulence

What is wake turbulence?

Formation of wingtip vortices

As an aircraft generates lift, a pressure differential forms between the upper and lower surfaces of the wing. High pressure air beneath the wing flows outward and around the wingtip towards the low pressure region above, creating a circular flow.

This motion results in swirling vortices that trail behind each wingtip, rotating in opposite directions. The vortex from the left wing rotates counterclockwise, while the right wing's vortex rotates clockwise when viewed from behind the aircraft.

The strength of these vortices is proportional to the weight, speed, and wingspan of the generating aircraft. Heavier, slower aircraft with larger wingspans, like transport category jets, produce the most intense vortices.

The rapidly spinning air in wingtip vortices poses a significant hazard to trailing aircraft, especially smaller airplanes. Encountering this turbulent air can induce an uncontrollable roll, cause structural stress, or result in sudden altitude loss.

Factors affecting vortex strength

An aircraft's weight, speed, and configuration significantly impact the intensity of the wake turbulence it generates. Heavier aircraft produce stronger wingtip vortices due to greater lift requirements. Slower speeds also increase vortex strength as the wings operate at higher angles of attack to maintain lift.

During takeoff and landing, aircraft operate in a "dirty" configuration with flaps and landing gear extended. This allows the wings to generate lift at slower speeds but also results in stronger vortex generation. As speed increases after takeoff and flaps and gear are retracted, the "clean" configuration reduces wake intensity.

Pilots and controllers mitigate these risks through separation standards based on aircraft weight categories. The greatest spacing is required behind "super" and "heavy" aircraft, especially during approach and landing when speeds are slow and configurations are dirty. Avoiding flight below and behind heavier aircraft is critical to preventing hazardous wake encounters.

Wake turbulence hazards

Induced roll and loss of control

Wake vortices can cause significant rolling moments on an encountering aircraft. The lower wing experiences an upward force as it crosses the upwash from a vortex, while the upper wing hits downwash, creating a strong rolling motion.

In some cases, this induced roll may exceed the roll authority of the encountering aircraft. Even with full opposite aileron deflection, the pilots may be unable to counteract the imposed roll, leading to a potentially unrecoverable loss of control situation.

The strength of the vortices and the dimensions of the encountering aircraft play a key role. Smaller aircraft with short wingspans are especially susceptible when flying into the wake of considerably larger planes. Avoiding the flight path of heavier aircraft, especially at low altitudes, is vital for preventing hazardous wake turbulence encounters.

Altitude deviations and structural stress

Wake turbulence can induce significant altitude changes in encountering aircraft. The updrafts and downdrafts within the vortices may exceed the climb performance of the following aircraft, resulting in an uncontrolled descent.

This sudden change in altitude not only risks loss of control, but also imposes severe structural loads on the airframe. Wing bending, tail stress, and even localized structural failure can result from the turbulent forces imparted by a wake encounter.

To mitigate these hazards, pilots must maintain vertical separation from heavier aircraft, especially during takeoff and landing phases. Crossing above or landing beyond the flight path of the preceding aircraft allows wake vortices to sink below the encountering aircraft's trajectory. Strict adherence to ATC wake separation minima is critical to prevent dangerous wake encounters and ensure the structural integrity of aircraft.

Critical phases: takeoff and landing

Wake turbulence poses the greatest hazards to aircraft during the takeoff and landing phases of flight. At low altitudes, there is little time or room to recover if an encountering aircraft gets upset or rolls inverted after flying into the wake vortices of a preceding aircraft.

However, several factors make wake turbulence especially problematic during these critical phases. Aircraft are flying at slow speeds with high-lift configurations, conditions which generate strong vortices. Heavy aircraft require higher angles of attack during takeoff and landing, intensifying the wake turbulence left behind. And smaller aircraft with less roll control authority are more susceptible to being overpowered if they encounter the vortices.

Therefore, pilots must be especially vigilant when taking off or landing behind larger aircraft. Aim to lift off prior to their rotation point and stay above their flight path. Touch down beyond where they landed. If uncertain, wait 2-3 minutes for the vortices to dissipate before taking off or landing. Strict adherence to ATC separation requirements is critical to ensure safety during these high-risk phases of flight.

Wake turbulence avoidance strategies

Vertical separation techniques

Wake turbulence poses a serious hazard to aircraft, especially during the critical landing phase. The powerful vortices generated by a heavy aircraft can easily upset a smaller plane following too closely behind and at the same altitude.

The key to safely avoiding wake turbulence on approach is to stay above the flight path of the preceding aircraft. Aim to maintain vertical separation and fly at a higher altitude than the plane in front. Then plan to touch down at a point farther down the runway, beyond where the lead aircraft landed.

Adhering to these vertical separation techniques on landing allows the dangerous vortices to sink below your flight path. You can safely fly above the turbulent air while still maintaining a stabilized approach to the runway. Proper spacing, both vertical and horizontal, is critical to preventing a wake turbulence encounter that could lead to loss of control at a vulnerable moment.

Lateral avoidance on takeoff

Taking off behind a larger aircraft poses a significant wake turbulence risk. The vortices generated by the larger plane can linger in its takeoff path, potentially upsetting a smaller aircraft that flies into them.

The key to avoiding this hazard is to get airborne before the larger aircraft's rotation point and maneuver laterally away from its climb path. By lifting off earlier, you avoid the strongest portion of the vortices. Then by turning to the upwind side, you let the vortices drift away from your flight path with the wind rather than following along behind the larger plane.

If a crosswind from the right is present, turning slightly to the right after takeoff will provide the most separation from the vortices that will be drifting to the left of the big plane's path. Communicating your offset plan to ATC prior to takeoff will help them accommodate your wake turbulence avoidance maneuver. With smart lateral offset planning and execution, you can safely depart behind larger aircraft.

Time-based separation

Time-based separation provides a safe buffer between aircraft by ensuring an adequate time interval between successive operations. Rather than relying solely on distance, time-based separation accounts for the movement and dissipation of the wake vortices.

When a pilot is unsure of the safe separation distance from the preceding aircraft, waiting 2-3 minutes before taking off or landing allows the vortices to dissipate to a less hazardous level. Although the optimal interval varies based on aircraft types and weather conditions, this general guideline provides an additional safety margin.

By delaying an operation for this period when separation distances are unclear, pilots can more confidently avoid dangerous wake encounters on departure or final approach. Exercising this precaution is especially prudent for light aircraft following heavy aircraft, whose vortices pose the greatest upset hazard.

Air traffic control and wake turbulence

Aircraft wake categories

Aircraft are divided into wake turbulence categories based on their maximum takeoff weight (MTOW):

• Super: Aircraft with MTOW over 560,000 lbs (254,011 kg). This includes the Airbus A380 and Antonov An-225.
• Heavy: Aircraft with MTOW between 300,000 lbs and 560,000 lbs (136,078 - 254,011 kg). Examples are the Boeing 747, 777 and Airbus A340.
• Large: Aircraft with MTOW between 41,000 lbs and 300,000 lbs (18,597 - 136,078 kg). This covers most narrow and wide-body airliners like the Boeing 737, 757, Airbus A320 and A330.
• Small: Aircraft with MTOW under 41,000 lbs (18,597 kg), which includes most business jets and turboprops.

The wake turbulence category determines the minimum separation required between aircraft:

• 8 NM (14.8 km) between a small aircraft behind a super
• 7 NM (13.0 km) between a large aircraft behind a super
• 6 NM (11.1 km) between a heavy aircraft behind a super; a small aircraft behind a heavy; or a small aircraft landing behind a heavy on the same runway
• 5 NM (9.3 km) between a heavy behind another heavy; or a small or large behind a heavy

With the implementation of new wake turbulence re-categorization methodologies, some of these separation minima may be reduced at certain airports to increase capacity while maintaining safety. But in general, the larger the difference in aircraft size, the greater the separation required to avoid hazardous wake encounters.

Wake turbulence advisories

Air traffic controllers issue wake turbulence advisories to warn pilots of the potential hazards posed by the wake of a preceding aircraft. These cautions are most common during the approach and landing phases, when aircraft are typically flying slowly at low altitudes with high-lift configurations - conditions that produce strong vortices.

Controllers will provide the position, altitude, and direction of flight of a heavy or super aircraft to any aircraft they judge may be adversely affected by its wake. The advisory includes the words "caution, wake turbulence" to underscore the potential danger. However, after this initial warning, it remains the pilot's responsibility to maintain a safe separation and avoid the area of likely wake turbulence.

Pilots should adjust their flight path or delay their takeoff or landing as needed to steer clear of a preceding aircraft's wake, remaining above its flight path and touching down beyond its landing point. Strict adherence to ATC's wake turbulence avoidance procedures and separation minima is critical to preventing hazardous wake encounters during these vulnerable phases of flight. Pilot vigilance and proactive avoidance tactics are the keys to steering clear of this invisible but potentially dangerous threat.

Wake turbulence is a critical safety hazard in aviation that all pilots must be vigilant of, especially when operating near larger aircraft during takeoff and landing. By understanding the mechanics of wingtip vortex formation, the factors influencing vortex strength, and proven avoidance strategies like maintaining vertical separation and allowing sufficient time for vortex dissipation, pilots can mitigate the risks of hazardous wake encounters. Ongoing technological and procedural advancements offer promise for further enhancing wake turbulence awareness and airport efficiency in the future.