AIM DECODED

3-1-1. General

By Chris Palmer, 2x Master Aviation Educator · Gold Seal CFI · Updated May 21, 2026

AIM 3-1-1 All of Chapter 3 →

AIM Text

  1. There are two categories of airspace or airspace areas:
    1. Regulatory (Class A, B, C, D and E airspace areas, restricted and prohibited areas); and
    2. Nonregulatory (military operations areas [MOA], warning areas, alert areas, controlled firing areas [CFA], and national security areas [NSA]).
  2. Within these two categories, there are four types:
    1. Controlled,
    2. Uncontrolled,
    3. Special use, and
    4. Other airspace.
  3. The categories and types of airspace are dictated by:
    1. The complexity or density of aircraft movements,
    2. The nature of the operations conducted within the airspace,
    3. The level of safety required, and
    4. The national and public interest.
  4. It is important that pilots be familiar with the operational requirements for each of the various types or classes of airspace. Subsequent sections will cover each class in sufficient detail to facilitate understanding.

Source: FAA Aeronautical Information Manual · current edition · paragraph 3-1-1.

Research Notes

AIM 3-1-1 introduces the airspace classification system — the foundation of U.S. airspace structure.

The two top-level categories:

  • Regulatory airspace: Class A, B, C, D, E airspace; restricted areas; prohibited areas. Operations require specific authorizations and equipment.
  • Nonregulatory airspace: MOAs, warning areas, alert areas, controlled firing areas. Operations are permitted but require special awareness of activity.

The six FAA airspace classes (A-G):

  • Class A: FL180 - FL600. IFR-only.
  • Class B: Around the busiest airports. Tiered cylinder. ATC clearance required.
  • Class C: Around airports with radar approach control. Two-way comms + Mode C required.
  • Class D: Around tower-controlled airports without radar approach. Two-way comms required.
  • Class E: Other controlled airspace. No mandatory comms for VFR.
  • Class G: Uncontrolled airspace. No ATC services.

Connection to FAR Part 91: § 91.126-135 govern operations in each airspace class. AIM Chapter 3 is the operational companion — explaining the procedures and rationale behind the regulatory requirements.

Reference: § 91.126 - § 91.135; AIM 3-1; AIM 3-2 (Controlled Airspace).

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