I strongly suspect the bulk of this 500MB is DRM frameworks for their in-flight video playback that they can't or don't want to support in-browser. Safari kicks

I strongly suspect the bulk of this 500MB is DRM frameworks for their in-flight video playback that they can't or don't want to support in-browser. Safari kicks video playback over to the United app each time you select something to watch and it does what appears to be a multi-stage hand-off dance.