You can't, but if you stay away from the runway part, cops won't chase you.
I did drive Luis into the airport in a cop car and did not get any problems, but I don't know whether that was just a fluke.
by passing all the missions without cheating
All you have to do press triangle.
Go to the airport in Shoreside Vale. When you are entering the airport on the entrance road there will be a parking lot to your right - or to your left if you're leaving - and you need to go in there. There are always a few cars in there and there is always a Cheetah but I'm warning you that the doors may be locked in it. That's the only way I know to get a Cheetah without stealing one that's driving off of the street.
Stories Without Words was created in 1987.
You could fly right into the state if you wanted to for example Philadelphia International Airport (PHI) or Pittsburgh International Airport (PIT). If you only want to get close without entering the state you could consider Newark Liberty International Airport (EWR).
You are scared because if you enter water and you can not swim, you could drown. Real people can not become mermaids, that is just for stories.
you can't
Some stories don't need them, a lot of stories work perfectly fine without them, as there can be a fair share of Action, violence, competition, or rivalry without them.
If you get off your flight, and leave the airport without claiming your luggage from the carousel.
Sikkim is the state without an airport or any railway routes.
Geneva Airport is all in Switzerland, but it is on the border and it is possible to access the airport from France and catch a plane without officially entering Switzerland. Basel Airport is the other way around. The airport is in France, but there is a fenced off road leading from Basel city to the airport. You can then check in and board a flight without having to (legally) enter France.