A bird was flying in the sky.
A UFO is flying in the sky.
UFO stands for unidentified flying object.
That place's food is great and their prices are good but the fly in the ointment is their terrible location.
It will cost you $100 to fly to the island.
That outfit is running a fly-by-night operation.
Those birds build their nests in the summer and fly to the south in the winter.
Look at that flying bird.
You can fly across America in about five hours.