Edgecases: planes that are already flying cannot take off and/or be in an airport; planes that are landed cannot land again and must be in an airport, etc.
because planes that are already flying cannot take off and/or be in an airport; planes that are landed cannot land again and must be in an airport, etc.
Edgecases: planes that are already flying cannot take off and/or be in an airport; planes that are landed cannot land again and must be in an airport, etc.