The two adult pandas, Mei Xiang and Tian Tian, and their 3-year-old cub, Xiao Qi Ji, are scheduled to be loaded into crates that day and driven in trucks to a FedEx Boeing 777 called the Panda Express. They will then be flown 19 hours from Dulles International Airport to China, where they will join about 150 other pandas in a lush nature preserve in the misty mountains of Sichuan Province. And with that, an era of panda diplomacy will end, at least for now. It began when Patricia Nixon,…