AIM Text
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.
Source: FAA Aeronautical Information Manual · current edition · paragraph 3-1-2.
Research Notes
AIM 3-1-2 covers Controlled Airspace — the regulatory framework for the various controlled airspace classes.
What makes airspace 'controlled': ATC has authority and responsibility for traffic separation in controlled airspace. Aircraft operating IFR must have ATC clearance. VFR aircraft have varying requirements depending on the class.
The controlled airspace hierarchy: Class A > B > C > D > E. Each lower class has progressively less restrictive entry requirements but provides progressively less ATC service to VFR aircraft.
VFR weather minimums (§ 91.155): Each class has specific minimum visibility and cloud clearance for VFR operation. Class A is IFR-only. Class B requires only 3 SM and clear-of-clouds. Class C-E (below 10,000 MSL) require 3 SM and 500/1,000/2,000 cloud clearance. Class E above 10,000 MSL requires 5 SM and 1,000/1,000/1 SM (the 5-1-1-1 rule).
Reference: § 91.155 (VFR weather mins); § 91.126-135; AIM 3-2.