Airspace is the portion of atmosphere controlled by a country above its territory, including its territorial waters. It is also defined as the space lying above the earth or above a certain area of land or water.
There are two kinds of airspace which include: Uncontrolled and Controlled airspace.
In the past, all airspace was uncontrolled, when there were a few airplanes that had no instruments necessary to fly in clouds. Even in the busiest airports, traffic density was very low and airplanes flew slowly. Although there we no conditions that aircraft could fly in, it was agreed upon that if one remained clear of clouds and had at least one-mile visibility you could see other airplanes and terrain in time to avoid a collision. This was known as see and avoid.
Having invented inexpensive gyroscopic flight instruments, travel through the clouds became possible thus see and avoid became useless. Procedures to ensure aircraft separation were needed hence this led to the creation of air traffic control (ATC) and controlled airspace.
There are different classifications of airspace i.e. A, B, C, D, E airspace.
This is airspace from 18,000 feet mean sea level, flight level 600 and airspace overlying the waters within 12 nautical miles of the coast of the 48 contiguous states and Alaska. All operation in Class A airspace is conducted under instrument flight rules unless authorized otherwise.
This is airspace from the surface to 10,000 feet MSL surrounding the nation’s busiest airports in terms of airport operations or passenger enplanements. Class b airspace is designed to contain all published instrument procedures once an aircraft enters the airspace. Air traffic control clearance is required for all aircraft to operate in the area and all aircraft that are so cleared receive separation within the airspace.
This is airspace from the surface to 4,000 feet above the airport elevation surrounding those airports that have an operation control tower, are serviced by a radar approach control and have a certain number of IFR operations or passenger enplanements. Each aircraft must establish two-way radio communications with the ATC facility providing air traffic services prior to entering the airspace and thereafter must maintain those communications while within the airspace.
This is airspace from the surface to 2,500 feet above the airport elevation surrounding those airports that have an operational control tower. The layout of each Class D airspace area is individually tailored and when instrument procedures are published the airspace is normally designed to contain the procedures. Each aircraft must establish two-way radio communications with the ATC facility providing air traffic services prior to entering the airspace and thereafter maintain those communications while in the airspace unless otherwise.
Class E airspace is the controlled airspace not classified as class A, B, C and D.
Special Use of airspace
It is the designation for airspace in which certain activities must be confined. Special use airspace consists of: Prohibited, restricted, warning, military operation, alert and controlled firing areas.