Need help assigning runway using time

Hi there,
I am trying to model a simple air traffic control system and have plane, flight_info and runway tables. Flight_info is a relational table and 2 of its attributes are pointers to the plane and runway tables so that I can allocate planes and flights to runways.

The length of the runway needs to be more than the stopping distance of the plane and I have a getStoppingDistance method to use for this. I guess one part will be to compare the length of the runway with the stopping distance.

I also need to assign a runway to a flight for a fixed time for each flight. I'm not sure how I can achieve this. I am thinking that I will need to test the 'state' attribute of the runway table to see if a particular runway is allocated or not and if it isn't, assign it to a flight. But I'm not sure how I would assign it for a fixed time.

Any help or suggestions on this would be great.reset the "state" attribute of runway everytime the flight completes landing. you could write a trigger on flight_info table which shall toggle this runway.state when you update flight_info