Definition
The Federal Aviation Regulation that requires pilots to comply with ATC clearances and instructions. It states that no pilot in command may deviate from an ATC clearance unless an amended clearance is obtained, an emergency exists, or the deviation is in response to a traffic alert and collision avoidance system resolution advisory. It also requires pilots, when given priority by ATC in an emergency, to submit a written report if requested.
Plain English
This is the rule that says you must do what ATC tells you to do. You can only deviate from a clearance if ATC gives you a new one, you have an emergency, or your collision avoidance system tells you to maneuver.
Context Anchor
Seen when studying air traffic control instructions, clearances, and the pilot’s responsibility after receiving directions from a controller.
Derivation
CFR stands for Code of Federal Regulations. Title 14 covers Aeronautics and Space, Part 91 contains the General Operating and Flight Rules, and section 91.123 is the specific paragraph addressing compliance with ATC clearances and instructions.
Why Pilots Care
Noncompliance without justification can result in regulatory violations, enforcement action, or compromised safety.
Intuition Check
Do not read this as just a page reference in a handbook. It is a binding federal rule that tells pilots what they must do when air traffic control issues an instruction or clearance.
Example Sentence 1
Under 14 CFR 91.123, the pilot requested an amended clearance before deviating around the thunderstorm.
Example Sentence 2
During an engine emergency the pilot deviated from the assigned altitude, knowing that 14 CFR part 91, section 91.123 permits such action when safety demands it.