How are these three planes supposed to coordinate

However, only one airport,located on the equator,has granted permission for the experiment,making it the starting point,the finish line,and the only spot where the planes can land,takeoff,or refuel on the ground.How should the three planes coordinate so the professor can fly continuously for the whole trip and achieve his dream without anyone running out of fuel and crashing?Pause here if you want to figure it out for yourself.