Definition
An authorization issued by air traffic control for an aircraft to proceed under specified traffic conditions within controlled airspace. The clearance is intended to prevent collisions between known aircraft; it is not an authorization to deviate from any rule, regulation, or minimum altitude, nor to conduct unsafe operations.
Plain English
Permission from air traffic control to do something specific — like take off, land, fly a route, or change altitude — based on the traffic around you at that moment. It keeps known aircraft from running into each other, but it does not relieve the pilot of responsibility for flying safely and legally.
Context Anchor
You encounter ATC clearances during radio communication with air traffic control, especially before taxi, takeoff, landing, route changes, altitude changes, and instrument flight operations.
Derivation
From the everyday word 'clearance,' meaning permission to proceed. In ATC use, it has the narrower meaning of permission granted under specific conditions, not a general 'all clear.'
Why Pilots Care
In controlled airspace a pilot may not legally fly without this authorization; receiving and correctly following it prevents mid-air conflicts and keeps the flight legal.
Intuition Check
Do not assume “clearance” means unlimited permission. An ATC Clearance is permission with specific instructions or limits, and the pilot still must fly safely and follow the rules.
Example Sentence 1
After holding short for two minutes, the pilot received an ATC clearance to taxi to runway 27 via taxiway Alpha.
Example Sentence 2
After takeoff the tower issued an ATC clearance to turn left and climb to 3,000 feet.