To fly and go against nature's law required one to be a Daoist of the Immortal Realm. To make something other than oneself fly, however, only required one to be a Daoist of the Unshackled Spirit Realm.
The most basic and popular "vehicle" for Daoists was a flying sword. Anyone who had broken through to the Unshackled Spirit Realm would immediately use their sword as one and roamed the sky with it.
Flying ships were used by wealthy Daoists or those who travelled with a lot of people. A huge amount of Qi was required to utilize it, which was why it was only popular among wealthy and strong Daoists.
Whoosh!
"Since when did you learn Daoism, Sister Hou?"
"I haven't."
"Then…how can you ride a flying sword?"
"I just can."
"That doesn't make any sense." Chang Yu frowned. "How can you make your sword fly without even being a Daoist of the Unshackled Spirit Realm?"