It your running the line dry its a tank deal,when you say downline are you standing the plane on its head or just at say a 45 degree angle.In flight like allen said the fuel goes to the back of the tank and shouldn't be a prob.Myself I worry more about the nose of the plane being pointed up than down ,can't say that I have even ran out of fuel going down ,the Plane has always made it to the ground *LOL* Good luck and lets us know what you find.