Wake Turbulence
Wake turbulence is the invisible, rotating air mass left in the wake of an aircraft in flight, comprising primarily wingtip vortices. It represents one of the most dangerous and underestimated hazards in aviation, particularly for light aircraft following heavy aircraft on approach or departure.
Wake Turbulence Behaviour
- Vortices sink at approximately 400–500 ft/min initially, then level off at about 900 ft below the generating aircraft
- They drift downwind at approximately the wind speed — a 10-knot crosswind moves a vortex 10 knots downwind
- In calm conditions, both vortices drift outward from the runway — one into the adjacent runway, one off the side
- Vortices persist for 1.5–3 minutes — longer in calm, stable conditions
- They dissipate with wind, turbulence, and ground effect
ATC Wake Turbulence Separation
ICAO and TC prescribe minimum separation standards based on the weight categories of both the generating and following aircraft. Heavy behind heavy: 4 NM; medium behind heavy: 5 NM; light behind heavy: 6 NM. Special categories (Super = A380) require even greater separation. ATC applies these standards automatically; pilots must be aware and may request additional separation.
On the TC Written Exam
Wake turbulence is extensively tested. Know: vortex behaviour (sink, drift, duration); avoidance strategies; ATC separation standards; that wind is the key variable in vortex drift.
Related Terms
See also: Vortices/Wingtip Vortices, Landing Sequence.