What does commercial flights mean?

The dividing line is not the size of the aircraft but the purpose of the flight. If somebody pays for the carriage of people, freight or mail, the operation is commercial, and the operator needs a certificate, approved procedures, trained and checked crews, an approved maintenance organisation and specific insurance. A privately owned business jet flown for its owner is not commercial; the identical aircraft chartered out for a fee is. European rules use the term commercial air transport and define it as the carriage of passengers, cargo or mail for remuneration or other valuable consideration.

In the United States, scheduled airline service is flown under Part 121 of the Federal Aviation Regulations, while smaller on-demand and commuter operations fall under Part 135; both are commercial. Europe wraps the same territory into a single concept, with operational rules in the Air Operations regulation and an air operator certificate behind every flight. The practical effect is the same everywhere: duty-time limits, minimum equipment lists, cabin crew requirements, reporting obligations and periodic audits by the national authority that private flying does not carry.

Within the commercial category, a scheduled flight is published in advance and sold seat by seat to the public; a charter is sold as a whole aircraft to a tour operator, a sports team or a government. Freight-only services, wet leases in which one airline supplies aircraft and crew to another, and air ambulance work carried out for payment all count as well. What none of them share with general aviation is the legal expectation that a paying stranger can step aboard and rely entirely on the operator's certification.