Airspace Classes

Airports · 6 min read · Mar 29, 2022
Airspace classes

Up in the skies, we do not have roads, traffic signs, traffic lights, or any of the resources that allow us to have certain control over the traffic as we do on the ground.

Yet, there are times when we can see several aircraft operating at the same time, and we can see their contrails crossing one over the other. However, the number of accidents is minimal when compared to ground transportation.

So, how is that possible? The answer is thanks to airspace classes. If you want to learn more about them, keep reading and discover all the details.

What are airspace classes?

Airspace classes can be defined as the areas of airspace determined for aircraft to fly under specific conditions. In general, there are two categories, namely controlled airspace and uncontrolled airspace.

However, in the United States, the Federal Aviation Administration created what they call the National Airspace System to help air traffic services such as air traffic control ensure the safety of aircraft flying over the territory.

The National Airspace System includes two other categories apart from controlled airspace and uncontrolled airspace. These are special use airspace and others.

Moreover, it is relevant to mention that the main categories are divided into airspace classes identified by letters. For example, classes A, B, C, D, and E belong to the controlled airspace category, and Class G airspace belongs to uncontrolled airspace.

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The letters represent the order from the most restricted areas to the least restricted ones for the controlled airspace classes. These are the classes that are subject to air traffic control regulations.

All pilots must learn the rules associated with each airspace. Depending on the class of airspace, there are weather conditions that must be met to fly according to Visual Flight Rules. Classes A, B, C, D, and E all have separate rules on visibility and mandatory cloud clearing. Pilots study the weather limits and other regulations for each class of airspace in an attempt to maintain the safety of travel.

With this in mind, let’s get into the details of each of the classes in the controlled airspace category first.

An airplane flying through a class B airspace in a mountainous region on a cloudy day.

Class A airspace

Class A airspace typically starts at 18,000 feet, means sea level or MSL, and covers up to 60,000 feet to what is called “flight level 600”.

Operation in Class A requires the Instrument Flight Rules to be in place, and it usually sees the higher-performance airplanes from both airlines and cargo operators flying in it.

Class B airspace

Class B airspace refers to the space around the most active airports in America measured from the ground to 10,000 feet MSL.

The class B airspace comprises different layers with thicknesses and forms adapted to the airspace requirements depending on the specific case. Class B airspace layers usually become bigger or broader the higher the aircraft flies.

To operate in a Class B airspace, flights must receive clearance from Air Traffic Control (ATC), and pilots must follow any further instructions. Of course, regulations are very strict in this class because air traffic control needs to deal with a lot of traffic.

Class C airspace

Class C airspace is similar to class B in the fact that this airspace involves the surroundings of some airports. The main difference is that these airports are not as busy as those defined as having class B airspace around. The main characteristics here are that the airports must have operational control towers and radar approach control.

Class C airspace is measured from the ground to 4,000 feet up above the elevation of the airport, and it is usually divided into two layers.

The first layer is generally called the inner circle, which is about 5 nautical miles, and the second layer, called the outer ring, is around 10 nautical miles and starts from 1,200 feet of altitude to the top at 4,000 feet, as was mentioned above. However, the layers are adapted to each specific case as it happens with class B airspace.

Constant communication with ATC is required when entering and operating within this airspace class.

Class D airspace

We mentioned before that the letters used to define the airspace classes also refer to the level of restriction. So, we have spoken about the most restrictive ones already, classes A, B, C.

Now, class D airspace can be seen as less restricted airspace because class D airspace is found around smaller airports that are not the busiest airports in the region but still have a control tower.

Starting from the surface up to 2,500 feet above airport elevation, the layers are also adapted to each individual case. Two-way communications are necessary prior to and during the use of class D airspace.

Class E airspace

Class E airspace is a particular type of controlled airspace. It is said that most American airspace is classified as Class E airspace since it involves all airspace that does not fall in any of the previous classes.

Control levels in Class E airspace are designed in accordance with aircraft flying under Instrument Flight Rules (IFRs), and the aircraft flying under Visual Flight Regulations (VFRs) generally are able to maneuver freely within this airspace class.

Given its nature, there are different configurations for class E airspace. For example, within CONUS (The contiguous United States), it usually starts at 1,200 feet above ground level (AGL) extends up to 18,000 MSL, and aircraft flying at 10,000 feet MSL and above are required to use Automatic Dependent Surveillance-Broadcast or ADS-B. However, it may start at around 700 feet AGL in some areas.

Class G airspace

Class G airspace is uncontrolled airspace and is the portion of airspace that does not fall in any of the previous classes.

Class G runs from a surface to the starting point of the overlying airspace, usually class E. Here, air traffic control has no authority nor responsibility within this class, so pilots can basically do what they want as long as they adhere to the Visual Flight Rules minimum requirements and avoid things like low-altitude aerobatics or conducting activities that may pose a hazard to people or objects on the ground.

Many American airports fall under class G airspace since they have no controls. Therefore, pilots must use the onboard radio to coordinate take-off and landing operations with other aircraft within the area.

An US Airforce military pilot in training, flying through military operations areas.

Special Use Airspace

Airspace may be limited to particular activities, or aviation activities may be restricted in certain areas. Those are known as “special use airspace” or “special operation areas”.

In other words, special use airspace, also known as Special Area of Operation or SAO, is defined as the airspace that requires to be limited for certain operations.

The main special use airspace areas include prohibited, Military Operations Areas (MOAs), restricted, warning zones, alert areas, and Controlled Firing Areas (CFAs).

Let’s take a look at some of them.

Prohibited areas

This is a section that prohibits flights for non-authorized aircraft. These areas are often created to ensure the security or other important factors related to national safety. These areas are listed in the US Federal Register and on an aeronautical chart.

Popular prohibited areas include Camp David and the National Mall over the White House and Congress buildings. When viewed on the chart, you will see the designations with “P” together with a number. You should always be aware of prohibited locations on your route.

Military Operations Areas

A Military Operations Area is an airspace designated for training military pilots. MOAs create vertical and horizontal airspace to separate IFR from military training flights.

While IFR traffic may be cleared through MOA, it is only possible when the ATC allows the IFR to be separate from the military operations. When the separation is not possible, redirection of the IFR traffic applies.

Also, traffic flying under VFR may be allowed into MOA, but it is recommended to avoid this situation.

Restricted areas

There are areas where the operation could potentially pose risks to aircraft, and these are frequently linked with military operations. However, the restricted area is not necessarily an MOA, so flying through these areas may be possible.

However, while it is possible for an aircraft to fly on these locations, it requires approval and confirmation that any military action is not taking place.

The risk is significant if access is done without authorization, and the hazards may include things like artillery firing and aerial gunnery.

Warning zones

Warning zones act the same as restricted areas. Essentially the United States does not possess a single jurisdiction.

These locations usually extend from 3 NM to the coast of the United States and involve areas where operation can be dangerous to non-participating aircraft.

The main purpose is to alert pilots about possible dangers. Warning zones can be located in international waters too, and they are marked with a W.

Alert areas

Alert areas are those involving a lot of flight training or where unusual aerial activity may be found.

While aircraft that are not part of the activity may be allowed in this space, pilots must be aware that training may occur at this time. In addition, the prevention of collisions is equally the responsibility of both parties, those entering and exiting the alert zone.

Alert areas may appear on an aeronautical chart with the letter A followed by a number.

Controlled Firing Areas

Also called CFAs, these are areas in which potentially dangerous activity is possible. However, they do not appear anywhere on any chart, and the activities can be stopped immediately when a non-interventional aircraft appears in the radars or is identified by ground or airborne cameras.

No non-participative aircraft need to alter its course when flying through CFAs.

A commercial airliner flying through class A airspace on a cloudy day.

Other airspaces

Finally, while there is no such thing as class F airspace, other airspace classifications exist.

Standard airspace classifications in this category include Air Defense identification zones (ADIZ), Terminal Radar Service Area (TRSA), parachute jump aircraft operations, Military Training Routes (MTR), Temporary Flight Restrictions (TFR), National Security Areas (NSA), among others.

Keep in mind that if you want to become a pilot, it is important to learn all about them. But do not worry, although they seem to be many, they are simpler than you think.

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Carlos Collantes
Carlos Collantes
A mechanical engineer and aviation enthusiast dedicated to share some knowledge by creating top-notch content, especially in engineering and aviation topics.

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