National Airspace System


  • The National Airspace System (NAS) is the network of United States airspace, air navigation facilities, services, airports, regulations, procedures, technical information, manpower, and material shared jointly between the Federal Aviation Administration (FAA) and the military
  • Airspace is classified based on the activities therein which must be confined because of their nature
  • There are 4 types of airspace that fall under 2 categories:
  • Categories of Airspace:

    • Regulatory (Class A, B, C, D, and E, restricted, prohibited areas, etc.)
    • Non-regulatory (warning areas, alert areas, military operating areas, etc.)
  • Types of Airspace:

  • Categories and types of airspace are dictated by:

    • Complexity
    • Density
    • Nature of operations
    • Level of safety required
    • National and public interest
  • To conform to international aviation standards, the United States adopted the primary elements of the classification system developed by the International Civil Aviation Organization (ICAO)

Sectional Airspace Summary
Figure 1: Airspace Summary

Controlled Airspace:

  • A generic term that covers the different classification of airspace and defined dimensions within which air traffic control service is provided to Instrument Flight Rules (IFR) flights and to Visual Flight Rules (VFR) flights in accordance with the airspace classification
  • IFR Requirements

    • IFR operations in any class of controlled airspace requires that a pilot must file an IFR flight plan and receive an appropriate ATC clearance
  • IFR Separation

    • Standard IFR separation is provided to all aircraft operating under IFR in controlled airspace
  • VFR Requirements

    • It is the responsibility of the pilot to ensure that ATC clearance or radio communication requirements are met prior to entry into Class B, Class C, or Class D airspace. The pilot retains this responsibility when receiving ATC radar advisories. (See 14 CFR Part 91)
  • Traffic Advisories

    • Traffic advisories will be provided to all aircraft as the controller’s work situation permits
  • Safety Alerts

    • Safety Alerts are mandatory services and are provided to ALL aircraft
  • Ultralight Vehicles

    • No person may operate an ultralight vehicle within Class A, Class B, Class C, or Class D airspace or within the lateral boundaries of the surface area of Class E airspace designated for an airport unless that person has prior authorization from the ATC facility having jurisdiction over that airspace. (See 14 CFR Part 103)
  • Unmanned Free Balloons

    • Unless otherwise authorized by ATC, no person may operate an unmanned free balloon below 2,000 feet above the surface within the lateral boundaries of Class B, Class C, Class D, or Class E airspace designated for an airport. (See 14 CFR Part 101)
  • Parachute Jumps

    • No person may make a parachute jump, and no pilot−in−command may allow a parachute jump to be made from that aircraft, in or into Class A, Class B, Class C, or Class D airspace without, or in violation of, the terms of an ATC authorization issued by the ATC facility having jurisdiction over the airspace. (See 14 CFR Part 105)

Uncontrolled Airspace:

  • Uncontrolled airspace or Class G airspace is the portion of the airspace that has not been designated as Class A, B, C, D, or E. It is therefore designated uncontrolled airspace

Special Use Airspace:

  • Special Use Airspace (SUA) consists of airspace of defined dimensions identified by an area on the surface of the earth wherein activities must be confined because of their nature, or wherein limitations are imposed upon aircraft operations that are not a part of those activities, or both
  • Except for Controlled Firing Areas, all SUA are charted on IFR or visual charts and include the area name or number, effective altitude, time and weather conditions of operation, the controlling agency in the chart panel
  • The period of time during which a designation of special use airspace is in effect is stated in the designation
  • The horizontal limits of special use airspace are measured by boundaries described by geographic coordinates or other appropriate references that clearly define their perimeter
  • The vertical limits of special use airspace are measured by designated altitude floors and ceilings expressed as above mean sea level
    • Note that unless otherwise specified, the word "to" (an altitude or flight level) means "to and including" (that altitude or flight level)
  • When operating within SUA, Air Traffic Control (ATC) assigned airspace (ATCAA), or altitude reservations (ALTRV), flights shall be conducted under the prescribed operational area procedures appropriate to the airspace area and operation
  • SUA is technically separate and should not be confused with other airspace
  • Certain special use airspace areas can create limitations on the mixed use of airspace
  • When in conjunction with military operations you may hear the term MARSA, or Military Assumes Responsibility for Separation of Aircraft
  • Special use airspace descriptions (except CFAs) are contained in FAA Order JO 7400.8, Special Use Airspace
  • On National Aeronautical Navigation Products (AeroNav Products) en route charts, this information is available on one of the end panels
  • A list of current special use airspaces can be found on the FAA's Special Use Airspace Query page

Military Training Explanation
Figure 2: VFR Corridor and Border Crossing Routes, San Diego

Other Airspace:

Sectional Airspace Legend
Figure 3: Airspace Legend


It is of the utmost importance that aircraft operating independently or under the control of a ground, ship, or airborne controller remain within the specified vertical and horizontal limits of assigned airspace. Remaining within assigned airspace can only be achieved by maintaining a total awareness of details depicted in current charts, publications, and military directives, coupled with a continual assessment of the accuracy of the controlling agency's radar. It may be required to operate with self-imposed vertical and horizontal buffers to remain within assigned airspace. When operating in designated SUA, aircrews should be aware that civilian aircraft may not honor the existence of such areas, nor monitor radio frequencies to receive appropriate warning/ advisories

Rules, Regulations & Procedures:


  • Airspace is charted and include hours of operation, altitudes, and the controlling agency (except CFAs)
Charts, Maps and More!


  • The national airspace system's present configuration is a reflection of the technological advances concerning the speed and altitude capability of jet aircraft, as well as the complexity of microchip and satellite-based navigation equipment
  • Chapter 3 of the Aeronautical Information Manual, and part 71 of the Code of Federal Regulations (CFRs) provide dimensions, exceptions, geographical areas covered, exclusions, specific transponder or equipment requirements, and flight operation information
  • It is important that pilots be familiar with the operational requirements for each of the various types or classes of airspace
  • When overlapping airspace designations apply to the same airspace, the operating rules associated with the more restrictive airspace designation apply
    • Refer to Code of Federal Regulations (CFRs) for specific dimensions, exceptions, geographical areas covered, exclusions, specific transponder or equipment requirements, and flight operations
      • Regulatory airspace is established and governed through 14 CFR Part 73 through the rule making process
Sectional Military Operating Area Airspace Hours
Figure 4: Military Operating Area Airspace Hours