Definition
The federal regulation that establishes the pilot in command (PIC) as directly responsible for, and the final authority as to, the operation of the aircraft. It also permits the PIC to deviate from any rule in Part 91 to the extent required to meet an in-flight emergency, and requires a written report to the Administrator upon request when such a deviation occurs.
Plain English
This is the rule that says the pilot in command is in charge of the aircraft and is the one responsible for what happens during the flight. In an emergency, the pilot is allowed to break other flight rules if doing so is necessary to handle the situation, but may have to explain it in writing afterward.
Context Anchor
You will see this rule in discussions of pilot responsibility, aeronautical decision-making, emergencies, and the authority of the pilot in command.
Derivation
14 CFR means Title 14 of the Code of Federal Regulations, which is the section of U.S. federal law covering aeronautics and space. Section 91.3 is a specific paragraph within Part 91, the rules for general operating and flight rules. Knowing the address (Title 14, Part 91, Section 3) makes it easier to look up and recognize when instructors or examiners cite it.
Why Pilots Care
It establishes that the pilot in command holds ultimate legal responsibility and decision authority during flight.
Intuition Check
Do not read 14 CFR Section 91.3 as a suggestion or best practice. It is a federal rule that assigns legal responsibility and authority to the pilot in command.
Example Sentence 1
Under 14 CFR Section 91.3, the captain elected to descend below the assigned altitude to clear icing, then filed a written report describing the emergency.
Example Sentence 2
The student reviewed 14 CFR Section 91.3 to understand why the instructor retained final authority on every training flight.