Definition
A regulation in Title 14 of the Code of Federal Regulations (14 CFR Part 91) that requires the pilot in command to comply with the operating limitations specified in the approved Airplane Flight Manual, markings, and placards for the aircraft being flown. Among these limitations are the maximum weight and the center of gravity (CG) range established by the manufacturer.
Plain English
It is the rule that says a pilot must fly the aircraft within the limits the manufacturer set, including weight and balance limits. Loading the aircraft outside those limits is a violation of this rule.
Context Anchor
Seen in weight and balance discussions because maximum weight, center-of-gravity limits, and loading instructions are operating limits the pilot must follow.
Derivation
Section comes from a Latin word meaning “to cut.” In a regulation, a section is one specific cut-out or numbered part of a larger set of rules. Here, 91.9 points to one specific rule within Part 91, the general operating rules for civil aircraft.
Why Pilots Care
Failure to ensure airworthiness before flight violates regulations and can lead to accidents or enforcement action.
Intuition Check
Do not read “section 91.9” as a page or section of the handbook. Here it means a specific federal aviation rule that pilots must follow.
Example Sentence 1
The instructor reminded the student that exceeding the airplane's maximum gross weight would put the flight in violation of section 91.9.
Example Sentence 2
The instructor reminded the student that section 91.9 makes the pilot in command responsible for the final airworthiness decision.