content: It would work if the runway were banked progressively steeper toward the outside. With the right banking there is zero lateral force on the landing gear. There are three actual physics-based problems. First, the takeoff lift becomes the sum of the gravitational weight and the centrifugal weight. This is a show-stopper. The extra structural strength needed would make the plane heavier, which is catastrophic for fuel efficiency. Efficiency is the king that rules the land of civil aviation. Second, mishaps would be very difficult owing to the banking. The plane has to choose the radius that matches its speed, otherwise the lateral forces will be unacceptable. Imagine what would happen if a plane braked too far up the slope and then caught on fire. It would be tricky to safely evacuate the passengers. The fire fighting equipment would have to fight an uphill battle on a slope banked for 500 knots. Burning fuel would run downhill, escaping from underneath firefighting foam, necessitating a system of drains everywhere in the runway with frequent maintenance. Third, the rim of the runway bowl is likely to create unpredictable vortices under high wind conditions. The rudder would have to be controlled by an advanced AI. On the other hand, these people have clearly identified the inherent transportation efficiency of circular routes. Perhaps we could use conventional linear runways, and use a circular route to shuttle planes between the runways and the terminal. Underground tunnels with a tow train for the planes would work but be extravagantly expensive. How about a series of small terminals around the outside of the runways, and a subway train to carry passengers between them in an endless loop?  Like the DFW airport but without planes dodging each other on the runways.