Just get the Black Chocobo, how to fly?

i already complete the quest i believe i can fly, and i can use my company chocobo to fly in Falcon Nest.
But in other area (not finish tune all aether current), i want to use the Black Chocobo to fly, but cannot do that. is it i missing something?

Thank you!

You need to collect the currents for all of your mounts, not just your company chocobo. So when you finish collecting those you'll be able to fly in each of the zones using whichever chocobo you'd like.

Or can you not use the black one in Falcons Nest for some reason?

You must attune with all the aether currents in each zone in order to be able to fly in that zone. The black chocobo is not an exception to that requirement.

Adding onto what has been mentioned, you have to attune to all the aether currents in a zone in order to fly there. This is done in two separate ways, physically locating the current and clicking on it to attune (like you would attuning to an aetheryte), or unlocking it automatically by completing certain sidequests and main scenario quests that feature the aether current as a quest reward. The former appear as a greenish white swirling ball of energy in various places around the zone.

These do not show up on the mini map or main map, however you can narrow down their location by opening your Key Items list and using the Aether Compass that was given to you when you gained the Black Chocobo. The aether compass will tell you the direction of the nearest aether current and a rough distance to it based on yalms. Quest currents are a little trickier although a quest that unlocks a current will have the '+' symbol on it's icon to show that it unlocks new content.

Or you could just cheat and look at the locations online, like here of course. ;)

Thanks all of your help.
I'm understand now.