Often listening to airline radio chatter, particularly to air traffic control, you’ll often hear radio transmissions using the term “heavy.” It has a fairly literal meaning, referring to the aircraft’s maximum takeoff weight. But it also indicates something else – the amount of turbulence a plane might leave in its wake.
Aircraft between a certain weight range are designated as “heavy.” Photo: BoeingAircraft categorized by weight size
In the United States, there are four classes of aircraft; small, large, heavy, and super. Only the terms heavy and super get commonly used. In a 2015 document, the Federal Aviation Administration defines small aircraft as those with a maximum takeoff weight of 41,000 pounds or less. Large aircraft are defined as those with a maximum takeoff weight of more than 41,000 pounds up to 300,000 pounds. The FAA defines heavy aircraft as those with a maximum takeoff weight of 300,000 pounds or more. These heavy aircraft don’t have to be operating at that weight, but they still get designated as heavy. Only the Airbus A380-800s and Antonov An-225s are designated as super aircraft.
The International Civil Aviation Organization (ICAO) has a slightly simpler way of categorizing aircraft. Light aircraft are those with a maximum takeoff weight of 15,500 pounds or less. Medium aircraft are those weighing more than 15,500 pounds but less than 300,000 pounds. Heavy aircraft are those weighing 300,000 pounds or more.
Big planes like A380s can leave miles of turbulent air in their wake. Photo: Airbus“Heavy” also designates the amount of turbulence a plane leaves in its wake
On this level, these designators are simply one way of classifying aircraft by size. But there’s a practical reason for doing this as well. Generally, the bigger the plane, the bigger the wake turbulence. Wake turbulence is rotating air produced by an aircraft’s wing as it takes off or lands. The more intense the turbulence, the greater the danger for the following aircraft
Usually, when identifying the plane to ATC, pilots will add the heavy descriptor to conversations with ATC to indicate that they should put some space between their plane and the next plane.
If you are in a small commuter turboprop, you’ll need miles of separation between your flight and an A380 preceding you. Get too close, and the wake turbulence can literally flip a light plane. On the other hand, two small commuter aircraft don’t need much separation at all.
Small aircraft like Dash-8s need to keep their distance from big aircraft. Photo: DeHavillandDistances vary depending on aircraft size
That same 2015 FAA document specifies how much distance ATC should put between planes. If you are a small plane following a super aircraft, the minimum spacing is eight nautical miles. Even a heavy aircraft (say a Boeing 747-400) following a super aircraft gets a minimum spacing of six nautical miles.
The minimum distance reduces as the maximum takeoff weights get smaller. A large aircraft following a heavy aircraft only needs five nautical miles. A heavy aircraft following another heavy aircraft only needs a space of four nautical miles. A small turboprop following a Boeing 747 needs a minimum distance of six nautical miles.
It doesn’t matter who a super aircraft follows; they can comfortably tag along behind with a spacing of just two and half nautical miles.
So while the term “heavy” refers to the maximum takeoff weight of the plane, it’s also used as a heads-up for other aircraft in the vicinity to give the plane some distance. Like so many things in aviation, it’s all about safety.

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