What does heavy mean for air traffic control?

Answer 1

When aircraft generate lift to fly, they leave an area of disturbed air behind them known as wake turbulence which can badly affect the control of following aircraft. This is especially dangerous during takeoff and landing, where the loss of control close to the ground can easily cause a crash.

The heavier the aircraft, the stronger the wake turbulence. For this reason, the interval is increased in most instances for aircraft following or landing behind a heavy aircraft.

The International Civil Aviation Organization (ICAO) uses three standard size classifications for planes based on their maximum takeoff weight;

Heavy : 136,000+ Kg

Medium : 7,000 - 125,599 Kg

Light : 7,000 kg or less.

In the United States, aircraft capable of a maximum takeoff weight of 300,000 pounds or more are classified as "heavy", even if the aircraft happens to be operating below that weight. Aircraft with a maximum takeoff weight over 14,500 pounds and less than 300,000 pounds are classified as "large". Aircraft with a maximum takeoff weight of 14,500 pounds or less are classified as "small".

There is a new category called 'super' which has been introduced just for the Airbus A380 and Boeing 747-800.

The separation between two "Supers" following each other is 4 nautical miles (nm). A large aircraft behind a super needs 10 nm separation.

The distance between two "heavy" craft is also 4 nm, a "large" or "medium" following a "heavy" needs 5 nm.

To make other craft aware of the status of heavies and supers, air traffic controllers controlling aircraft in the vicinity of airports use the convention of including the "heavy" or "super" weight classification in the aircraft call sign - "United 29 Heavy", for example. Controllers also issue a cautionary advisory to aircraft landing behing a heavy or super - "...following a heavy Boeing seven sixty seven, caution wake turbulence".