Aviation Glossary - Clearance

Clearance

An authorization by air traffic control for the purpose of preventing collision between known aircraft, for an aircraft to proceed under specified traffic conditions within controlled airspace. The pilot-in-command of an aircraft may not deviate from the provisions of a visual flight rules (VFR) or instrument flight rules (IFR) air traffic clearance except in an emergency or unless an amended clearance has been obtained. Additionally, the pilot may request a different clearance from that which has been issued by air traffic control (ATC) if information available to the pilot makes another course of action more practicable or if aircraft equipment limitations or company procedures forbid compliance with the clearance issued. Pilots may also request clarification or amendment, as appropriate, any time a clearance is not fully understood, or considered unacceptable because of safety of flight. Controllers should, in such instances and to the extent of operational practicality and safety, honor the pilot's request. 14 CFR Part 91.3(a) states: "The pilot in command of an aircraft is directly responsible for, and is the final authority as to, the operation of that aircraft." THE PILOT IS RESPONSIBLE TO REQUEST AN AMENDED CLEARANCE if ATC issues a clearance that would cause a pilot to deviate from a rule or regulation, or in the pilot's opinion, would place the aircraft in jeopardy. (See ATC INSTRUCTIONS.) (See AIR TRAFFIC CONTROL CLEARANCE.)

source: FAA Pilot/Controller Glossary

ATC permission for an aircraft to proceed under specified traffic conditions within controlled airspace, for the purpose of providing separation between known aircraft.

source: FAA Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25A)

ATC permission for an aircraft to proceed under specified traffic conditions within controlled airspace, for the purpose of providing separation between known aircraft. Code of Federal Regulations (CFR). Regulations issued by the U.S. Federal Government as published in the Federal Register.

source: FAA Weight Shift Control Handbook (FAA-H-8083-5)

phraseology referring to authorisation: expect onward clearance at time 38
removal of an obstacle: snow clearance is under way
distance between a moving object and a potential obstacle: monitor our wing tip clearance; the engine ground clearance on the B737 is quite small

source: ICAO English Pro Aviation Glossary

The act of clearing or something (such as a space) cleared
The distance between two moving objects, especially between parts of a machine
The height or width of a tunnel, bridge or other passage, or the distance between a vehicle and the walls or roof of such passage; a gap, headroom.
A permission for a vehicle to proceed, or for a person to travel.
A permission to have access to sensitive or secret documents or other information
A sale of merchandise at a reduced price.

source: Wikitionary / Wikipedia and Related Sources (Edited)