The term “wake turbulence” is used in this context to describe the effect of the rotating air masses generated behind the wing tips of large jet aircraft, in preference to the term “wake vortex” which describes the nature of the air masses. Detailed characteristics of wake vortices and their effect on aircraft are contained in the Air Traffic Services
Planning Manual (Doc 9426), Part II, Section 5.
Wake turbulence categories of aircraft:
Wake turbulence separation minima shall be based on a grouping of aircraft types into three categories according to the maximum certificated take-off mass as follows:
a) HEAVY (H): all aircraft types of 136 000 kg or more;
b) MEDIUM (M): aircraft types less than 136 000 kg but more than 7 000 kg; and
c) LIGHT (L): aircraft types of 7 000 kg or less.
Helicopters should be kept well clear of light aircraft when hovering or while air taxiing.
Note 1: Helicopters produce vortices when in flight and there is some evidence that, per kilogram of gross mass, their vortices are more intense than those of fixed-wing aircraft.
Indication of heavy wake turbulence category:
For aircraft in the heavy wake turbulence category the word “Heavy” shall be included immediately after the aircraft call sign in the initial radiotelephony contact between such aircraft and ATS units.