It's late—I must fly.

已经晚了—我得赶快走。

《牛津词典》

youdao

If you must fly, be sure to pack light to cut down the plane's load.

如果你必须坐飞机，一定要轻装上阵，减少飞机的载重。

youdao

Whatever the cause, the message for exhausted elderly travellers would appear to be: if you must fly, head west.

ECONOMIST: Biology: Go west, old man | The

En route to their destination, planes must fly over the control centers instead of a straight line, wasting fuel and time.

FORBES: Magazine Article

Some flight schools reacted immediately to the new threat of dangerous student pilots who, at some point, must fly alone to pass tests.

CNN: graphic