How to dair after a uair?

[Mambo490]

I was watching Westballz stream and he was giving a combo, one part of the combo was an uair, then immediately do a dair. When tried doing this, I couldn't dair, I just uair and I can't dair after, how do I do this? BTW i'm using Falco

 

[Hoagie]

I'm not to sure to be honest, but the only thing I can think of is do you use the c-stick to execute aerial attacks? I know that this is a lot easier and lets you make moves a lot faster than using the normal stick.

 

[Firejew]

1. post video
2. get answer

 

[Mambo490]

I don't get what they are doing, they use two aerials in mid air, like he uair and then dairs right away

 

[Firejew]

Are they near a platform? They touch the edge and slide off, putting you back into falling animation for another opportunity to attack.
Maybe it's a FJ u-air into d-air? I'm not sure if it's actually possible but if you were to jump and while rising (and probably close to frame perfectly) u-air instantly and then the d-air comes out.
Again, post a video of what you're looking for. Even find the footage again and we can figure it out immediately. Text and explaining is the worst method of communicating a visual.