Often listening to airline radio chatter, particularly to air traffic control, you’ll
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. Let’s explore the meaning and usage of this term..
In the United States, there are four classes of aircraft; small, large, heavy, and super.
Only the terms heavy and super are commonly used.
In a 2015 document, the Federal Aviation Administration (FAA) 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 between 41,000 pounds and 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 and Antonov An-225 are designated as super aircraft.
The I.C.A.O. ) 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 that weight
between 15,500 pounds and 300,000 pounds while havy aircraft are those weighing 300,000 pounds
or moreOn this level, these designators are simply one way of classifying aircraft by size.
However, there’s a practical reason for doing this as well.
Generally, the bigger the plane, the more significant 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.
That same aforementioned 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 like a Boeing 747-400 following a super aircraft
gets a minimum spacing of six nautical miles. Naturally, 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.
Therefore, while the term “heavy” refers to the maximum takeoff weight of the plane,
it’s also used as a warning for other aircraft in the vicinity
to give the plane some distance. Like so many things in aviation, it’s all about safety.
Did you know about the meaning and usage of this term? Let us know in the comments.