[3] (In earlier years "direct" in the OAG did mean "no plane change".)While so-called "direct" flights may thus involve changes in aircraft (a "change of gauge"), or even airline[3] at the intermediate point, they are typically—but not always—differentiated from "connecting flights" in that the airline will enforce a dependency between multiple legs of the flight, so that leg two cannot operate if leg one has failed to arrive at the departure airport.For example, flights that require stopover merely for refuelling usually do not permit passengers to disembark from the aircraft.On the other hand, flights where there is a change of aircraft (change of gauge) may require that passengers disembark and stay at a holding area for security reasons and a proper headcount.Airlines may also market connections to a consolidation airport, usually an airline hub, where the continuation of the flight from multiple aircraft is to a single aircraft listed under several flight numbers.
An illustration of a San Francisco to Singapore "non-stop" flight (green) versus a "direct" flight (purple)
