Definition
A type of commercial air carrier operation, certificated under 14 CFR Part 121, that conducts passenger or cargo flights on an unscheduled, on-demand basis rather than according to a published schedule. Supplemental operations include charter flights, all-cargo operations, and other non-scheduled service flown by certificate holders authorized to operate under the supplemental rules of Part 121.
Plain English
A commercial flight operation that is flown on demand or by charter rather than on a fixed published schedule, but is still held to the same high standard of rules as the major airlines.
Context Anchor
Seen in Federal Aviation Administration operating rules, air carrier certificates, operations specifications, and Part 121 air carrier discussions.
Derivation
Supplemental comes from the Latin supplementum, meaning something added to fill out or complete. These operations were historically seen as adding to (supplementing) the scheduled airline network by providing flights when and where scheduled service did not exist.
Why Pilots Care
Pilots flying supplemental operations are working under Part 121 rules — the strictest set of operating regulations in U.S. civil aviation — even though the flights themselves are not on a published schedule. Knowing whether your operation is scheduled or supplemental affects which sections of Part 121 apply to crew duty, dispatch, and flight planning.
Intuition Check
Do not read supplemental as simply meaning extra or optional. Here it means a specific regulatory category for certain paid air carrier flights.
Example Sentence 1
The cargo company holds a Part 121 certificate authorizing supplemental operations, allowing it to fly freight charters anywhere in the country on demand.
Example Sentence 2
Supplemental operations often involve cargo or passenger charters that do not follow fixed schedules.