Perhaps our definition of the entity Flight was not specific enough.
Is a
Flight the connection between take-off and landing? Clearly not, because
a Flight can continue on to additional destinations.
Is a Flight the itinerary I follow? No, as a passenger I may switch to another Flight or Airline.
There is a third concept here in addition to Flight and
itinerary (which we have not tried to model). There is a section of
a Flight between take-off and landing. Let's call it "Flight Segment".