UA.II.A.K4: Air Traffic Control (ATC) and the NAS.

ACS Area II — Airspace Classification and Operating Requirements Task A: Airspace Classification References: 14 CFRCode of Federal RegulationsCloseThe federal rulebook where Part 107, Part 89, Part 48, and other aviation rules live. part 71; ACAdvisory CircularCloseFAA guidance that explains acceptable ways to comply with rules or understand FAA procedures. 107-2; AIMAeronautical Information ManualCloseFAA operational guidance and glossary material used to understand aviation procedures and terminology.; FAAFederal Aviation AdministrationCloseThe U.S. aviation regulator responsible for Part 107 rules, airspace, and pilot certification processes.-H-8083-25; FAAFederal Aviation AdministrationCloseThe U.S. aviation regulator responsible for Part 107 rules, airspace, and pilot certification processes.-G-8082-22

Key Concepts

How the NAS Is Organized: Controlled vs. Uncontrolled

• The National Airspace System (NASNational Airspace SystemCloseThe shared U.S. airspace system that drones must operate within.) is grouped into regulatory and nonregulatory categories and four types: controlled, uncontrolled, special use, and other airspace. For exam purposes, know that controlled airspace includes Classes A, B, C, D, and E; uncontrolled airspace is Class G. The type and dimensions are driven by traffic density, operational needs, and safety considerations.^[1]
• Class A: generally from 18,000 feet MSLMean Sea LevelCloseAltitude measured from average sea level, not from the ground below you. up to and including FLFlight LevelCloseAltitude expressed using a standard pressure setting, mainly relevant to higher-altitude crewed aviation. 600, including airspace overlying waters within 12 NMNautical MileCloseA distance unit used in aviation. One nautical mile is about 1.15 statute miles. of the U.S. coastline (48 contiguous states and Alaska). Unless otherwise authorized, all operations in Class A are IFRInstrument Flight RulesCloseRules for operating primarily by instruments. On the exam, IFR often appears in weather, traffic, and airspace context..^[1][7]
• Class B: generally from the surface to 10,000 feet MSLMean Sea LevelCloseAltitude measured from average sea level, not from the ground below you. surrounding the nation’s busiest airports; each area is individually tailored and consists of a surface area and layered shelves.^[7]
• Class C and D: both are controlled airspace. Class D generally extends from the surface to 2,500 feet above the airport elevation (charted in MSLMean Sea LevelCloseAltitude measured from average sea level, not from the ground below you.); two-way radio communications must be established prior to entry and maintained while inside, and VFRVisual Flight RulesCloseRules for flight using visual reference and minimum weather conditions. aircraft do not receive separation services.^[6]
• Class E: controlled airspace not classified as A–D. In most areas the base is 1,200 feet AGLAbove Ground LevelCloseAltitude measured above the ground directly below the aircraft.; in many others it is the surface or 700 feet AGLAbove Ground LevelCloseAltitude measured above the ground directly below the aircraft.; some areas begin at a charted MSLMean Sea LevelCloseAltitude measured from average sea level, not from the ground below you. altitude. Class E typically extends up to, but not including, 18,000 feet MSLMean Sea LevelCloseAltitude measured from average sea level, not from the ground below you.. All airspace above FLFlight LevelCloseAltitude expressed using a standard pressure setting, mainly relevant to higher-altitude crewed aviation. 600 is Class E. Where charts do not depict a Class E base, Class E begins at 14,500 feet MSLMean Sea LevelCloseAltitude measured from average sea level, not from the ground below you.; this includes airspace overlying waters within 12 NMNautical MileCloseA distance unit used in aviation. One nautical mile is about 1.15 statute miles. of the U.S. coastline.^[2][6]
• Class G: uncontrolled airspace from the surface up to the base of the overlying Class E. VFRVisual Flight RulesCloseRules for flight using visual reference and minimum weather conditions. weather minimums still apply in Class G (know they exist; details are covered elsewhere).^[2]
• Special use airspace (SUASpecial Use AirspaceCloseAirspace where activities or restrictions may require extra attention, such as MOAs or restricted areas.) confines certain activities and may impose limitations on other operations; SUASpecial Use AirspaceCloseAirspace where activities or restrictions may require extra attention, such as MOAs or restricted areas. is depicted on instrument charts and affects how the NASNational Airspace SystemCloseThe shared U.S. airspace system that drones must operate within. is shared safely.^[2]

Regulatory references: controlled airspace operating rules and equipment requirements are in 14 CFRCode of Federal RegulationsCloseThe federal rulebook where Part 107, Part 89, Part 48, and other aviation rules live. Part 91, and the detailed designations/descriptions of the classes are in 14 CFRCode of Federal RegulationsCloseThe federal rulebook where Part 107, Part 89, Part 48, and other aviation rules live. Part 71.^[7]

ATC’s Role in Controlled Airspace

• Controlled airspace is where ATCAir Traffic ControlCloseThe system that manages controlled airspace, traffic flow, and aircraft separation services. provides service to IFRInstrument Flight RulesCloseRules for operating primarily by instruments. On the exam, IFR often appears in weather, traffic, and airspace context. flights and, per class, to VFRVisual Flight RulesCloseRules for flight using visual reference and minimum weather conditions. flights. For any IFRInstrument Flight RulesCloseRules for operating primarily by instruments. On the exam, IFR often appears in weather, traffic, and airspace context. operation in controlled airspace, the pilot must file an IFRInstrument Flight RulesCloseRules for operating primarily by instruments. On the exam, IFR often appears in weather, traffic, and airspace context. flight plan and receive an ATCAir Traffic ControlCloseThe system that manages controlled airspace, traffic flow, and aircraft separation services. clearance. Each Class B, C, and D area designated for an airport contains at least one primary airport.^[7]
• Air Route Traffic Control Centers (ARTCCs) provide ATCAir Traffic ControlCloseThe system that manages controlled airspace, traffic flow, and aircraft separation services. to aircraft operating on IFRInstrument Flight RulesCloseRules for operating primarily by instruments. On the exam, IFR often appears in weather, traffic, and airspace context. flight plans within controlled airspace during the en route phase and, when able, may provide advisory/assistance services to VFRVisual Flight RulesCloseRules for flight using visual reference and minimum weather conditions. aircraft. ARTCCs use Air Route Surveillance Radar (ARSRAir Route Surveillance RadarCloseLong-range radar used by en route ATC centers to detect and display aircraft traffic.) to detect and display en route traffic.^[5]
• On charts, ARTCCAir Route Traffic Control CenterCloseAn ATC facility that manages en route traffic over a large region. boundaries are identified with labeled lines, and sector frequencies appear in boxed callouts—know how to find these when planning near busy airways.^[3]
• Beneath Class B, you must establish and maintain communications with any control tower when transiting the surface areas of Class B, Class C, or Class D airports under that Class B airspace. Expect busy frequencies and maintain vigilance for mixed traffic types.^[4]

Navigating Busy Terminal Areas: Flyways, Corridors, and Chart Cues

• VFRVisual Flight RulesCloseRules for flight using visual reference and minimum weather conditions. Flyways on the reverse of many TACs are planning aids that suggest routes under/around Class B to help avoid major traffic flows. They are not clear of traffic—strict adherence to VFRVisual Flight RulesCloseRules for flight using visual reference and minimum weather conditions. rules and see-and-avoid is required.^[4]
• VFRVisual Flight RulesCloseRules for flight using visual reference and minimum weather conditions. Corridors are defined slices through some Class B areas where aircraft may operate without an ATCAir Traffic ControlCloseThe system that manages controlled airspace, traffic flow, and aircraft separation services. clearance or communication with ATCAir Traffic ControlCloseThe system that manages controlled airspace, traffic flow, and aircraft separation services.. Corridors have specific lateral and vertical limits; study the TACTerminal Area ChartCloseA large-scale chart used around busy terminal airspace where more detail is needed. carefully before using one.^[4]
• Chart depiction essentials frequently tested:
  • Class B: screened blue with a solid boundary line.^[3]
  • Class C: screened blue with a dashed boundary line and a boxed “C” following the primary airport name.^[3]
  • Class A on IFR high en route charts: open white background; it spans 18,000 MSLMean Sea LevelCloseAltitude measured from average sea level, not from the ground below you. to FL600Flight LevelCloseAltitude expressed using a standard pressure setting, mainly relevant to higher-altitude crewed aviation..^[3]
• Traffic Advisories: ATCAir Traffic ControlCloseThe system that manages controlled airspace, traffic flow, and aircraft separation services. may issue traffic calls such as “Traffic, 2 o’clock, one zero miles...” based on radar, visual, or pilot reports. These advisories are provided as workload permits and do not relieve the pilot of see-and-avoid responsibilities. ADS-BAutomatic Dependent Surveillance-BroadcastCloseAircraft broadcast technology. Part 107 drones generally may not use ADS-B Out unless specifically authorized. users may also receive Traffic Information Service–Broadcast (TIS-BTraffic Information Service-BroadcastCloseBroadcast traffic information service used in crewed aviation traffic awareness systems.), which rebroadcasts ATCAir Traffic ControlCloseThe system that manages controlled airspace, traffic flow, and aircraft separation services.-derived traffic information to enhance awareness.^[8]

Mastering these structures and services clarifies when ATCAir Traffic ControlCloseThe system that manages controlled airspace, traffic flow, and aircraft separation services. is providing separation, when only communications are required, where controlled airspace begins and ends (e.g., 14,500 feet MSLMean Sea LevelCloseAltitude measured from average sea level, not from the ground below you. for undeclared Class E, 2,500 feet above airport elevation for Class D), and how to use charts and planning tools to operate safely and legally in the NASNational Airspace SystemCloseThe shared U.S. airspace system that drones must operate within..^[2][6]