Maintenance, preventive maintenance, and alterations programs

This regulation requires Part 121 air carriers to establish and maintain comprehensive programs for all maintenance work on their aircraft. The carrier must ensure three key things:

First, all maintenance work—whether done by the airline's own mechanics or contracted out—must follow the procedures in the carrier's maintenance manual. This creates accountability and standardization.

Second, the airline must provide qualified personnel, proper facilities, and adequate equipment to perform maintenance correctly. You can't just have anyone with a wrench working on airliners.

Third, every aircraft must be confirmed airworthy before returning to service, with all maintenance properly completed according to Part 121 standards.

In practice, this means airlines operate under FAA-approved maintenance programs that govern everything from routine inspections to major repairs. As a pilot, you're flying aircraft maintained under these structured programs, which is why Part 121 operations have such strong safety records. The regulation puts the legal responsibility on the carrier to maintain a complete maintenance infrastructure.

*This is a plain-English summary for study only. The official 14 CFR text on this page is controlling — always read the current regulation and consult a CFI.*