Phys/Math ques on Centripital Force?

A 75 kg pilot flies a plane in a loop. At the top of the loop, where the plane is completely upside-down for a instant, the pilot hangs freely in the seat and does not push against the seat belt. The airspeed indicator reads 120m/s. What is the radius of the plane's loop? (I'm studying for a test and the answer is 1500 m but i don't know how to arrive at that answer, steps would be appreciated)