Spaceship pattern/wave

Hello, I am brainstorming a top down space shooter with alien ships coming from the top of the screen to the middle of the screen, shooting at the hero spaceship.

I am trying to figure out the best way to do waves in Actionscript. I would like some enemies to do patterns, come swoop down in a line and swoop up in a line… does anyone have any suggestions on how to help me with this?

Thanks in advance