Definition
A federal aviation regulation requiring that no person may operate an aircraft unless, within the preceding 12 calendar months, it has had either an annual inspection performed in accordance with 14 CFR part 43 and approved for return to service by an authorized person, or an inspection for the issuance of an airworthiness certificate. This rule applies to most general aviation aircraft not operated under a different inspection program.
Plain English
It is the rule that says most small aircraft must have a thorough inspection at least once every 12 months before they can legally fly.
Context Anchor
You will see this citation when checking aircraft maintenance records during preflight planning, especially when confirming that the annual inspection is current.
Derivation
14 CFR means Title 14 of the Code of Federal Regulations, which contains the rules for aviation. Part 91 covers general operating and flight rules. Section 91.409 is the specific rule about inspections, and the (a) points to the first paragraph, which deals with the annual inspection requirement.
Why Pilots Care
Failure to meet this requirement makes the aircraft unairworthy and illegal to fly, exposing the pilot to enforcement action and safety risk.
Intuition Check
Do not read this as a helpful recommendation or a maintenance note. It is a federal rule that sets a required inspection status before the aircraft may be operated.
Example Sentence 1
Before accepting the rental, she checked the logbook to confirm the annual inspection required by 14 CFR part 91, section 91.409(a) was still within the last 12 months.
Example Sentence 2
The flight school ensures every training aircraft receives its required 100-hour inspection under 14 CFR part 91, section 91.409(a).