Restriction or suspension of operation: Domestic and flag operations

This regulation requires airlines operating under Part 121 domestic or flag operations to restrict or suspend flights when they become aware of hazardous conditions. These conditions specifically include airport and runway hazards, though the regulation isn't limited to just those examples.

The key obligation is on the certificate holder (the airline) to act once they *know* about dangerous conditions. They must either restrict operations (such as limiting aircraft types, payloads, or operational procedures) or suspend them entirely until the hazard is corrected.

This puts a legal responsibility on airlines to make conservative safety decisions rather than attempting to operate in questionable conditions. For example, if an airline learns that a runway has significant ice contamination or that airport lighting is inoperative, they must stop or limit operations until the problem is fixed. The regulation emphasizes that commercial operators cannot simply defer to pilot judgment alone—the company itself must take action when hazards are known.

*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.*