Free safety module 3 of 7Airspace Classification & Air Traffic Control14 min readLast reviewed: 2026-09-19
US airspace classes (A, B, C, D, E and G), VFR weather minimums for each, transponder and ADS-B requirements including the Mode C veil, and the habits that prevent an unauthorized airspace incursion.
Scenario
VFR Transit Beneath Class B Shelves Near the Mode C Veil. You are routing VFR beneath the shelves of Class B airspace surrounding a major airport, inside the 30 NM Mode C veil. The Class B floor steps down from 4,000 ft MSL to 1,800 ft MSL as you approach the primary airport, and a Class D surface area sits just south of your track.
Decisions and actions
Plan to stay clearly below the floor of each Class B shelf, with a buffer for altimeter and navigation error, unless you hold an ATC clearance — Class B entry always requires a specific clearance (AIM 3-2-3).
Altimeter discipline: set the current altimeter setting of a station within 100 NM (14 CFR 91.121). An error of one inch of mercury is roughly 1,000 ft of indicated altitude.
Inside the Mode C veil — the airspace within 30 NM of a Class B primary airport, from the surface up to 10,000 ft MSL — an operable transponder with automatic altitude reporting and operable ADS-B Out are required unless ATC authorizes otherwise (14 CFR 91.215, AIM 3-2-3).
Check special use airspace (MOAs, restricted and prohibited areas), Class D surface areas and any TFRs on the current sectional and NOTAMs before you fly.
Safety traps
Climbing into a Class B shelf while avoiding terrain, birds or turbulence.
Losing track of position near shelf boundaries and Class D surface areas.
Assuming a filed VFR flight plan is an airspace clearance — it is not; a clearance must come from ATC.
Check your understanding
1. Under 14 CFR 91.155, what are the VFR visibility and cloud-clearance minimums in Class C airspace?
3 statute miles visibility; 500 ft below, 1,000 ft above and 2,000 ft horizontal from cloud
5 statute miles visibility, clear of cloud
1 statute mile visibility, clear of cloud
3 statute miles visibility, clear of cloud
Show answer
A. Class B, C and D airspace and Class E below 10,000 ft MSL all carry the same basic minimums under 91.155: 3 statute miles visibility, 500 ft below, 1,000 ft above and 2,000 ft horizontally clear of cloud. Class B differs only in that its cloud clearance is "clear of clouds".
2. What is the Mode C veil, and what does it require?
The 5 NM ring around any towered airport, requiring a working radio
The airspace within 30 NM of a Class B primary airport, surface to 10,000 ft MSL, requiring an operable transponder with automatic altitude reporting and operable ADS-B Out unless ATC authorizes otherwise
A restriction that applies only above 18,000 ft MSL
A VFR-only zone where transponders must be switched off
Show answer
B. AIM 3-2-3 defines the Mode C veil as the airspace within 30 nautical miles of a Class B primary airport, from the surface up to 10,000 ft MSL, where aircraft must carry an operable transponder with automatic altitude reporting and operable ADS-B Out unless otherwise authorized by ATC.
Educational use only. This module does not replace current regulations, the AIM, authorized weather briefings, the aircraft flight manual or instructor guidance. Verify operational information through official sources before flight.
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