National Airspace System

The National Airspace System, or NAS, is the network of United States airspace and all associated components.


Introduction

Introduction
  • The National Airspace System (NAS) is the network of United States airspace, air navigation facilities, services, airports, regulations, procedures, technical information, human resources, and material shared jointly between the Federal Aviation Administration (FAA) and the military.
  • The national airspace system is divided into categories and further classified by complexity, density, nature of operations, level of safety required, and national and public interest.
  • The FAA designs rules, regulations, and procedures pilots must follow depending on the airspace they operate within.
  • Airspace is generally charted to identify its location, hours of operation, altitudes, etc.
  • Nationally, the airspace is monitored and publically displayed using the Operational Information System.

Categories of Airspace

Categories of Airspace
  • There are two categories of airspace:
    • Regulatory Airspace.
    • Non-Regulatory Airspace.

    • Regulatory Airspace:

      • Regulatory airspace is subject to the rulemaking process of defining strict standards.
      • Regulatory airspace includes Class A, B, C, D, and E airspace areas and restricted and prohibited areas.

    • Non-Regulatory Airspace:

      • Non-regulatory airspace is a way to classify airspace and its associated purpose without subjecting it to the rulemaking process.
        • These standards, in one way or another, relate to improving safety while maximizing operational efficiency.
      • Non-regulatory includes military operations areas (MOA), warning areas, alert areas, controlled firing areas (CFA), and national security areas (NSA).

Types of Airspace

Types of Airspace
  • Airspace Summary
    Airspace Summary
  • Special Use Airspace Summary
    Special Use Airspace Summary
  • There are four types of airspace:
    • Controlled Airspace.
    • Uncontrolled Airspace.
    • Special Use Airspace.
    • Other Airspace.

    • Controlled Airspace:

    • Uncontrolled Airspace:

      • Uncontrolled or Class Golf Airspace areas are without air traffic controls but remain subject to overarching safety minimums outlined in FAA regulations. [Figure 1]
    • Sectional Airspace Summary
      Airspace Summary

    • Special Use Airspace:

      • Special Use Airspace (SUA) consists of defined dimensions identified by an area on the earth's surface wherein activities are confined because of their nature or wherein limitations are imposed upon aircraft operations that are not a part of those activities or both. [Figure 2]
      • In those instances where security requirements dictate, the Federal Aviation Administration establishes prohibited airspace to segregate surface areas from flight operations completely.
      • Like prohibited airspace, restricted airspace limits most flight operations but permits some when the controlling agency approves.
      • Warning areas, MOAs, alert areas, CFAs, and NSAs are non-regulatory special use airspace.
      • Special-use airspace descriptions (except CFAs) are contained in FAA Order JO 7400.8, Special Use Airspace.
      • Permanent SUA (except CFAs) is charted on Sectional Aeronautical, VFR Terminal Area, and applicable En Route charts and includes the hours of operation, altitudes, and the controlling agency.
        • For temporary restricted areas and temporary MOAs, pilots should review the Domestic Notices found on the Federal Notice to Airman System (FNS) website under External Links or the Air Traffic Plans and Publications website, the FAA SUA website, and/or contact the appropriate overlying ATC facility to determine the effect of non-depicted SUA areas along their routes of flight.
      • The horizontal limits of special use airspace are the boundaries described by geographic coordinates or other appropriate references that clearly define their perimeter.
      • The vertical limits of special-use airspace are the 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.
      • 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.
      • This information is available on one of the end panels of National Aeronautical Navigation Products (AeroNav Products) en route charts.
      • The FAA's Special Use Airspace Query page contains a list of current special-use airspaces.
      • Special use airspace is divided into:

      • Regulatory Special Use Airspace:

      • Non-Regulatory Special Use Airspace:

    • Special Use Airspace Summary
      Special Use Airspace Summary

    • Other Airspace:


Airspace Rules, Regulations, and Procedures

Airspace Rules, Regulations, and Procedures

  • Reduced Vertical Separation Minimum (RVSM):

    • Instrument Flying Handbook, Increase in Aircraft Permitted Between FL 180 and FL 410
      Instrument Flying Handbook, Increase in Aircraft Permitted Between FL 180 and FL 410
    • The FAA established the Reduced Vertical Separation Minimum (RVSM) to accommodate heavy traffic while maintaining safety.
    • Changing the separation above flight level (FL) 290 from 2,000' to 1,000' minimum adds six more flight levels while increases in equipment reliability maintain public safety.
    • Operators and aircraft must have received RVSM authorization from a responsible civil aviation authority.
    • With requirements met and authorization obtained, pilots can utilize the benefits of RVSM airspace.
    • Aircraft operating in the RVSM environment follow standard east (odd)/west (even) altitude routing for flights up to and including FL410.
    • Pilots experiencing non-standard operating conditions, either with the aircraft or environment, must follow specific procedures inside RVSM airspace.
    • Under certain circumstances, aircraft may receive accommodation to operate non-RSVM aircraft in RSVM airspace.
    • Instrument Flying Handbook, Increase in Aircraft Permitted Between FL 180 and FL 410
      Instrument Flying Handbook, Increase in Aircraft Permitted Between FL 180 and FL 410

  • Gulf of Mexico Flight Operations:

    • Gulf of Mexico Flight Operations involve operations in the Gulf.
    • Air traffic control (ATC) may apply 50 nautical mile (NM) lateral separation (i.e., lateral spacing) between airplanes authorized for Required Navigation Performance (RNP) 10 or RNP 4 operating in the Gulf of Mexico.
    • 50 NM lateral separation may be applied in the following airspace:
      • Houston Oceanic Control Area (CTA)/Flight Information Region (FIR).
      • The Gulf of Mexico portion of the Miami Oceanic CTA/FIR.
      • Monterrey CTA
      • Merida High CTA within the Mexico FIR/UTA.
    • Within the Gulf of Mexico airspace described above, pairs of airplanes whose flight plans indicate approval for Performance-Based Network (PBN) and either RNP 10 or RNP 4 may be spaced by ATC at lateral intervals of 50 NM.
      • ATC will space any airplane without RNP 10 or RNP 4 capability such that at least 90 NM lateral separation is maintained with other airplanes in the Miami Oceanic CTA and at least 100 NM separation is maintained in the Houston, Monterrey, and Merida CTAs.
    • The reduced lateral separation allows more airplanes to fly on optimum routes/altitudes over the Gulf of Mexico.
    • 50 NM lateral separation is not applied on routes defined by ground navigation aids or Gulf Area Navigation (RNAV) Routes Q100, Q102, or Q105.
    • Information useful for flight planning and operations over the Gulf of Mexico under this 50 NM lateral separation policy, as well as information on how to obtain RNP 10 or RNP 4 authorization, can be found in the West Atlantic, Gulf of Mexico, and Caribbean Resource Guide for U.S. Operators located at: https://www.faa.gov/headquartersoffices/avs/wat-gomex-and-caribbean-resource-guide.
    • Pilots should use Strategic Lateral Offset Procedures (SLOP) during regular Gulf of Mexico CTA operations. SLOP procedures and limitations are published in the U.S. Aeronautical Information Publication (AIP), ENR Section 7.1, General Procedures; Advisory Circular (AC) 91-70, Oceanic and Remote Continental Airspace Operations; and International Civil Aviation Organization (ICAO Document 4444, Procedures for Air Navigation Services – Air Traffic Management.

  • Mode C Transponder Requirements:

    • In general, the CFRs require aircraft to be equipped with an operable Mode C transponder and Automatic Dependent Surveillance-Broadcast (ADS-B) Out when operating:
      • In Class A, Class B, or Class C airspace areas.
      • Above the ceiling and within the lateral boundaries of Class B or C airspace up to 10,000 feet MSL.
      • Class E airspace at and above 10,000 feet MSL within the 48 contiguous states and the District of Columbia, excluding the airspace at and below 2,500 feet AGL.
      • Within 30 miles of a Class B airspace primary airport, below 10,000 feet MSL (commonly called the "Mode C Veil").
      • For ADS-B Out: Class E airspace at and above 3,000 feet MSL over the Gulf of Mexico from the coastline of the United States out to 12 nautical miles.
      • Transponder and ADS-B Out requirements do not apply to any aircraft not originally certificated with an electrical system or that has not subsequently been certified with such a system installed, including balloons and gliders.
        • These aircraft may conduct operations without a transponder or ADS-B Out when operating:
          • Outside any Class B or Class C airspace area; and;
          • Below the altitude of the ceiling of a Class B or Class C airspace area designated for an airport, or 10,000 feet MSL, whichever is lower.
    • 14 CFR Section 99.13 requires all aircraft flying into, within, or across the contiguous U.S. ADIZ to have a Mode C or S transponder.
      • Balloons, gliders, and aircraft not equipped with an engine-driven electrical system are exempt.
    • Pilots must ensure that their aircraft transponder/ADS-B is operating on an appropriate ATC-assigned VFR/IFR code with altitude reporting enabled when operating in such airspace. If in doubt about the operational status of either feature of your transponder while airborne, contact the nearest ATC facility or FSS, and they will advise you on what facility you should contact to determine the status of your equipment.

  • Automatic Dependent Surveillance-Broadcast:

    • Automatic Dependent Surveillance-Broadcast is surveillance technology deployed throughout the National Airspace System.
    • Position reports are based on satellite navigation systems (aircraft to aircraft).
    • ADS-B broadcasts once per second with the aircraft's position, velocity, identification, and other information.
    • It also receives this information from other aircraft.
    • The ADS-B system is composed of aircraft avionics and a ground infrastructure.
      • On-board avionics determine the aircraft's position using the Global Navigation Satellite System (GNSS) and transmit it with additional information about the aircraft to ground stations for use by ATC and other ADS-B services (approximately once per second).

  • UAS Airspace:

    • Small unmanned aircraft systems operations must be integrated into the NAS while maintaining operational capacity and safety without introducing an unacceptable risk to airspace users, persons, and property.
    • 14 CFR Part 107 was the first new rule dedicated to UAS operations.
    • For commercial operations, Part 135 and 137 operations considerations exist.
    • Public aircraft operations are also permitted.
    • When required, emergency operations are authorized.

Airspace Charting

Airspace Charting

Operational Information System (OIS)

Operational Information System (OIS)
  • Operational Information System
    Operational Information System (OIS)
  • OIS Advisory Example
    OIS Advisory Example
  • The Operational Information System (OIS) is the FAA's Air Traffic Control System Command Center (ATCSCC) near real-time National Airspace System (NAS) status information system. [Figure 4]
  • Operational Information System
    Operational Information System (OIS)

  • Advisories:

  • Ground Stops:

    • Ground stops are when aircraft are held on the ground and not allowed to take off.
    • ATCSCC may issue ground stops for several reasons, including:
      • To control air traffic volume to airports when the projected traffic demand exceeds the airport's acceptance rate for a short period.
      • To temporarily stop traffic to allow time to implement a longer-term solution, such as a Ground Delay Program.
      • The affected airport's acceptance rate drops to zero.
    • The most widespread use of this procedure was on September 11, 2001.

  • Ground Delay Programs:

    • The Ground Delay Program (GDP) is a traffic management process administered by the ATCSCC, which consists of holding aircraft on the ground.
    • The program aims to support the traffic management mission and limit airborne holding.
    • It is a flexible program, implemented in various forms depending on the needs of the air traffic system.
    • Ground delay programs provide for equitable assignment of delays to all system users.

  • Route Information:

    • Route information is available on the website and in specific advisories.
    • Some route information, subject to the 56-day publishing cycle, is located on the "OIS" under "Products," Route Management Tool (RMT), and "What's New" Playbook.
    • The RMT and Playbook contain routings for Air Traffic and NAS operators' use when coordinated "real-time," published in an ATCSCC advisory.
    • The word "Route" in the header identifies route advisories; the associated action is Required (RQD), Recommended (RMD), Planned (PLN), or For Your Information (FYI).
    • Operators are to file flight plans consistent with the Route RQD advisories.

  • Electronic System Impact Reports:

    • Electronic System impact reports are available at https://www.fly.faa.gov/ois/" under "System Impact Reports."
    • This page lists scheduled outages/events/projects and Traffic Management Initiatives.

Conclusion

Conclusion
  • The national airspace system's present configuration reflects the technological advances concerning aircraft's speed and altitude capability and the complexity of microchips and satellite-based navigation equipment.
  • It is of the utmost importance that aircraft remain within or clear of the specified vertical and horizontal limits of assigned airspace, as applicable.
    • Remaining within a particular 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.
    • Operating with self-imposed vertical and horizontal buffers may be required to remain within assigned airspace.
    • When operating in SUA, military traffic must be cognizant of civilian aircraft that may not honor the existence of such areas nor monitor radio frequencies to receive appropriate warnings/ advisories.
  • 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.
  • Pilots must be familiar with the operational requirements for each of the various types or classes of airspace.
    • Refer to Title 14 of the U.S. Code of Federal Regulations (CFR) for specific dimensions, exceptions, geographical areas covered, exclusions, specific transponder/ADS-B or other equipment requirements, and flight operations.
      • Regulatory airspace is established and governed through 14 CFR Part 73 through the rulemaking process.
  • When overlapping airspace designations apply to the same airspace, the operating rules associated with the more restrictive airspace designation apply.
  • NAS operators can access the OIS website at https://www.fly.faa.gov before filing their flight plan.
    • This information is useful for pre-flight planning, but remember, updates are published on a workload-permitting basis.
  • Not commonplace, there are other airspace designations, such as waivered airspace, that pilots may hear about but are impractical knowledge of everyday flight operations.
  • The United States adopted the primary elements of the classification system developed by the ICAO to conform to international aviation standards.
  • Read the FAA's guidance on entering, exiting, and flying in United States airspace to learn more about international flying.
  • Various air traffic control services are provided within controlled airspace, including:
    • Traffic advisories are provided to all aircraft as the controller's work situation permits.
    • However, air traffic control provides safety alerts to ALL aircraft.
  • Resources, such as AOPA's Know Before You Go: Navigating Today's Airspace, are available to help learn about the national airspace system and how to navigate it best.
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References

References