Airspace

National Airspace System

The United States National Airspace System (NAS) is a complex and highly regulated structure that governs where and how aircraft can operate. Understanding the NAS is essential for any pilot, as it directly affects route planning, communication requirements, and weather minimums. This section provides an overview of the primary airspace classifications—Class A, B, C, D, E, and G—including entry requirements and Visual Flight Rules (VFR) weather minimums.

Airspace Overview

The airspace over the United States is divided into controlled and uncontrolled airspace. Controlled airspace includes Class A, B, C, D, and E. Uncontrolled airspace is designated as Class G.

Each class of airspace is designed to meet the needs of different types of air traffic and safety considerations, with specific requirements for pilot certification, aircraft equipment, and communication.

Class A Airspace

Class A airspace extends from 18,000 feet MSL up to and including FL600 (60,000 feet), covering the entire continental U.S. and Alaska, including airspace overlying the waters within 12 nautical miles of the coast.

Entry Requirements

• Must operate under Instrument Flight Rules (IFR) only.

• ATC clearance is required (an IFR clearance).

• Aircraft must be equipped with a two-way radio, Mode C transponder, ADSB out, and DME or RNAV for navigation (above FL240).

• Pilot must hold at least a private pilot certificate with an instrument rating.

VFR Weather Minimums

• Not applicable. VFR flight is prohibited in Class A airspace.

Class B Airspace

Description

Class B surrounds the nation’s busiest airports (e.g., LAX, JFK, ATL). It generally extends from the surface to 10,000 feet MSL with individually tailored configurations resembling an upside-down wedding cake.

Entry Requirements

• ATC clearance is required prior to entry. (ie. ATC must say N123AB cleared into the Los Angeles Class B Airspace)

• Aircraft must have a Mode C transponder & ADSB out(within 30 NM of the airport—Mode C veil).

• Two-way radio communication must be established and maintained.

• Pilot must be at least a private pilot (or a student pilot with proper endorsements).

  • Student pilots can recieve an endorsement to enter a Class B airspace, however there are some Class B airspace that a student pilot cannot enter, even with an appropriate endorsement. This information can be found in AIM 3-2-3

VFR Weather Minimums

• 3 statute miles visibility.

• Clear of clouds.

Class C Airspace

Description

Class C surrounds airports with moderate traffic and radar service. It usually extends from the surface to 4,000 feet AGL, with a 5 NM radius core (surface to 4,000 AGL) and a 10 NM outer shelf (1,200 to 4,000 AGL).

Entry Requirements

• Establish and maintain two-way radio communication before entering.

• Aircraft must have a Mode C transponder & ADSB out.

VFR Weather Minimums

• 3 statute miles visibility.

• 500 feet below, 1,000 feet above, and 2,000 feet horizontal from clouds.

Class D Airspace

Description

Class D surrounds smaller towered airports, typically extending from the surface to 2,500 feet AGL with a radius of about 4 NM, though it can vary depending on airport layout, procedure requirements and overlying airspace.

Entry Requirements

• Establish and maintain two-way radio communication with the control tower prior to entry.

• A Mode C transponder & ADSB out IS NOT REQUIRED for entry into a class D airspace

VFR Weather Minimums

• 3 statute miles visibility.

• 500 feet below, 1,000 feet above, and 2,000 feet horizontal from clouds.

Class E Airspace

Description

Class E is controlled airspace not classified as A, B, C, or D. It starts at various altitudes and can extend up to but not including 18,000 feet MSL. It also exists above FL600.

It typically begins:

• At 1,200 feet AGL in many rural areas.

• At 700 feet AGL around many non-towered airports with instrument procedures.

• At the surface for some instrument airports.

Entry Requirements

• There are no entry requirements for Class E airspace

VFR Weather Minimums

• Below 10,000 feet MSL:

  • 3 statute miles visibility.

  • 500 feet below, 1,000 feet above, 2,000 feet horizontal from clouds.

• At or above 10,000 feet MSL:

  • 5 statute miles visibility.

  • 1,000 feet below, 1,000 feet above, 1 statute mile horizontal from clouds.

Class G Airspace (Uncontrolled)

Description

Class G is uncontrolled airspace, typically near the surface in rural or remote areas. It extends from the surface to the base of overlying Class E airspace.

Entry Requirements

• There are no entry requirements for Class G airspace

VFR Weather Minimums

Summary

Understanding Airspace Shelves

Both Class B and C airspace are structured with layered shelves, similar to an upside-down wedding cake. These shelves allow controllers to manage traffic efficiently around busy airports while giving VFR pilots opportunities to fly below or above the controlled airspace without entering it.

Many shelves of Class B and C airspace begin above the surface, allowing for flight underneath the overlying airspace without meeting the entry requirements.

When flying underneath an overlying Class C airspace (so you're in D, E, or G airspace) you must maintain 200 knots or less and you are not required to have a Mode C transponder, ADSB out, or establish and maintain two way radio communication.

When flying over a Class C airspace (below 10,000) you're required to have a Mode C transponder and ADSB out. But you do not need to establish and maintain two way radio communication.

When flying underneath an overlying class B airspace you do not need to establish and maintain two way radio communications, but you must have a Mode C transponder and ADSB out. (You are within the Mode C veil so you must have this equipment)

When flying over a Class B airspace you do not need to establish and maintain two way radio communications, but you must have a Mode C transponder and ADSB out. (You are within the Mode C veil so you must have this equipment)

Airspace Speed Restrictions

FAA regulations impose maximum speeds in certain classes of airspace and around airports for traffic flow and collision avoidance. These speed restrictions are mandatory, even for aircraft capable of flying faster.

➡ Important: These speed limits are regulatory (not just advisory) and are found in 14 CFR §91.117. You can, however, request exception from ATC if your aircraft is unable to fly below these speed limits safely. (Ex. if flying a large jet that is very heavy and is unable to maintain below 200 knots)

Understanding the structure of the National Airspace System is a fundamental aspect of safe and legal flight operations. As a pilot, knowing which airspace you’re in and what is required of you in terms of communication, equipment, and weather conditions can mean the difference between a smooth flight and a regulatory violation. Always consult current aeronautical charts and FAA publications when planning your flight.