National Airspace System

Category and Types of Airspace: AIM 3-1-1

There are two categories of airspace...

Regulatory

Class A, B, C, D, and E
Restricted Areas
Prohibited Areas

Non-regulatory

Military Operations Areas
Warning Areas
Alert Areas
Controlled Firing Areas
National Security Areas

Within these two categories, there are four types:

Controlled
Uncontrolled
Special Use
Other Use

Uncontrolled Airspace: AIM 3-3-(1-3)

Class G

Airspace not designated as Class A, B, C, D or E
No minimum requirements for VFR

Controlled Airspace

ATC services are provided.

Class Alpha: AIM 3-2-2

From 18,000’-FL600

Includes overlying waters within 12 nautical miles off the coast of the 48 contiguous states and Alaska.
Not charted on supplements

Operating Rules and Pilot/Equipment Requirements

FAR 91.135

IFR only
ATC Clearance
Mode-C Transponder (FAR 91.215)
DME for flights at or above FL240 (FAR 91.205 (e))
Instrument rating for airplane and pilot
Speed limit: Mach 1

Class Bravo: AIM 3-2-3

Surface-10,000 MSL
Resembles a very complicated and multi-tiered, upside down wedding cake.
Individually tailored
Surface area and two or more layers
Depicted in solid blue lines

Operating Rules and Pilot/Equipment Requirements

FAR 91.131

ATC Clearance
2-way radio communication
Minimum PPL
- Reference AIM 3-2-3 para. b-2 for specific Bravo airspace that prohibits any student pilot activity with a Bravo endorsement.
Mode-C Transponder (FAR 91.215)
ADS-B Out
250 KIAS under 10,000 MSL (FAR 91.117)
200 KIAS underlying shelf (FAR 91.117)

Class Charlie: AIM 3-2-4

Surface-4,000 AGL
5 nautical mile radius core
10 nautical mile radius shelf no lower than 1,200 ft up to 4,000 ft
Depicted in solid magenta

Operating Rules and Pilot/Equipment Requirements

FAR 91.130

2-way radio communication
Mode-C Transponder (FAR 91.215)
ADS-B Out
200 KIAS (FAR 91.117)

Class Delta: AIM 3-2-5

Surface-2,500 ft AGL
4 nautical mile radius

Note: individually tailored to fit airspace needs.

Depicted in dashed blue

Operating Rules and Pilot/Equipment Requirements

FAR 91.129

2-way radio communication
200 KIAS

Class Echo Airspace: AIM 3-2-6

S.E.T.V.O.D.A.

Surface: extends from the surface to the next airspace. Charted in dashed magenta.
Extension: designated as extensions to Class B, C, D, and E. Class E extension begins at surface up to the next controlled airspace. The purpose of an extension is to provide separation for an instrument approach.
Transition: designated for transitioning aircraft to/from the terminal or en route environment. Extends upward from 700 ft AGL depicted in vignette magenta or 1,200 ft AGL.
- Sometimes depicted in vignette blue, Echo begins at 14,500' MSL inside the vignette extending up to but not including 18,000' MSL. Outside the blue vignette, Class G extends from the surface to 1,200' AGL then become Echo above.
Victor Airways (Federal Airways): extends from 1,200 ft AGL up to but not including 18,000 ft MSL.
Offshore: extends from a specified altitude up to 17,999 ft MSL, starting 12 miles from the coast.
Domestic en Route
Above 1,200 AGL, 14,500 MSL and above FL600.

ADIZ: AIM 5-6-4

ADIZ: Air Defense Identification Zones have been established to facilitate early identification of all aircraft in the vicinity of U.S. Airspace.

Requirements:

- - Transponder
  - Two-way radio
  - Flight plan (IFR or DVFR [defense visual flight rules])
  - Frequent poition reports

Transponder and ADS-B Requirements: FAR 91.215, 225

📡 Transponder

A transponder is an electronic device on the aircraft that responds to radar signals from Air Traffic Control (ATC). When ATC radar “interrogates” your aircraft, the transponder sends back information.

✈️ It can send:

A squawk code (assigned by ATC)
Altitude information (if it’s a Mode C or Mode S transponder)
This helps ATC identify your aircraft on their radar screen and track your position and altitude.

🛰️ ADS-B Out

Automatic Dependent Surveillance–Broadcast.

Automatic – it transmits on its own without pilot input.
Dependent – it depends on onboard GPS for positioning.
Surveillance – it allows ATC and other aircraft to “see” your aircraft.
Broadcast – it constantly broadcasts your aircraft’s position, altitude, velocity, and identification to ATC and nearby equipped aircraft.

✈️ ADS-B Out is the part of the system that sends this data out.

Note: There’s also ADS-B In (optional), which lets you receive traffic and weather data.

Airspeed Restrictions: FAR 91.117, FAR 91.817

Below 2,500' AGL and within 4 nautical miles of primary airport or an underlying shelf or VFR Corridor: 200 kts.
Below 10,000' MSL: 250 kts.
No person may operate a civil aircraft in the United States above 10,000' MSL at a true Mach number greater than 1 unless in compliance with 91.818.

VFR Weather Minimums: AIM 3-1-4

Special Use Airspace: AIM 3-4-(2-8)

M.C.P.R.A.W.N.

Military Operations Areas
- VFR traffic should exercise extreme caution.
Controlled Firing Areas
- Not depicted on the sectional chart.
Prohibited Areas
- Completely off limits to traffic.
Restricted Areas
- Must obtain clearance from the controlling agency.
Alert Areas
- Extreme caution should be exercised.
Warning Areas
- Voluntarily avoid.
National Security Areas
- Voluntarily avoid.

Other Use Airspace: AIM 3-5-(1-9)

M.T.V.P.A.T.

Military Training Routes
- Three digits: at least one route above 1,500' AGL.
- Four digits: Entire route below 1,500' AGL.
- V: VFR route
- I: IFR route
Temporary Flight Restrictions
- To provide safety and protection for people or property.
VFR Routes: to provide navigation around, under and through complex airspace.
- Transition
- Corridors
- Flyways
Parachute Jump Areas
Airport Advisory Areas: only available in Alaska within 10 statute miles of an airport where a control tower is not operating but a FSS is located on the airport.
Terminal Radar Service Areas: a Class D airspace has radar service capabilities.
Weather Reconnaissance Areas
Special Air Traffic Rules
Special Flight Rules
- Depicted in blue squares along a circular border, see Washington DC area on sectional.

Although the SAC Legend is a good reference, use this FAA's Aeronautical Chart User's Guide for a far deeper dive into VFR/IFR Charts. It automatically updates every 65 days and has a very extensive legend.

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