From Longman Dictionary of Contemporary English(I) must fly(I) must flyspokenLEAVE A PLACE used to say that you must leave quickly → fly
Examples from the Corpus
(I) must fly• To keep your pilot's licence you must fly 5 hours each year minimum.• He is expected eventually to rule that the Union flag must fly, and he called the row unnecessary.• With me on his back he must fly down to the Gruncher.• If Jerba was picturesque, Nefta is magical and I regret that I must fly home in a week.• What is more, it is able to tell others what direction they must fly in order to get food themselves.• As a scheduled operator, Virgin must fly its 400-seat jumbos even if there are only a handful of passengers on board.• Second, it must fly swiftly away from the nest and alight some distance from it. 