Definition
The airspace within 30 nautical miles of the primary airport of a Class B airspace area, from the surface up to 10,000 feet MSL, within which aircraft must be equipped with an operable transponder having Mode C automatic altitude reporting capability.
Plain English
An invisible 30-mile circle drawn around a major airport. If you fly anywhere inside that circle below 10,000 feet, your aircraft must have a working transponder that automatically reports your altitude to ATC.
Context Anchor
You will encounter this term when planning a flight near a large airport, checking aircraft equipment requirements, or deciding whether your route can pass near Class B airspace.
Derivation
A 'veil' is a thin covering that drapes over something. The term pictures a transparent dome of altitude-reporting requirement draped over and around the Class B airport, even where the Class B airspace itself does not reach.
Why Pilots Care
Operating without Mode C inside a veil violates FARs and can trigger enforcement action or traffic conflicts.
Analogy
Think of it like an invisible ring around a busy airport. Crossing the ring does not automatically mean you are entering controlled airspace, but it does mean your aircraft usually needs the required altitude-reporting equipment.
Intuition Check
Do not treat the Mode C Veil as a separate class of airspace or as a radio communication area. It is mainly an equipment requirement: inside the veil, your aircraft usually must be able to report altitude electronically.
Example Sentence 1
Before departing the small grass strip, the pilot confirmed his Mode C transponder was working because the field sat inside the Mode C Veil of the nearby Class B airport.
Example Sentence 2
Because the aircraft lacked a working Mode C transponder, it remained outside the Mode C Veil during the cross-country flight.