Billboard camera alignment issue

Hello,

I’m trying to lock the billboard so that it is always parallel to the surface of the earth. I thought setting billboard.alignedAxis to Z should do this, but when I change the camera view angle to something other than pointing at the center of the earth, the billboard always faces the camera. Is there a way to lock the billboard so that it’s plane is always parallel to the earth’s surface?

Top down view:

Rotated horizon view:

I need the billboard image (aircraft) to stay parallel to the earth on camera rotation. Any help is appreciated.

thanks,

chad