Continual horizontal scrolling up and down

[ottz0]

I am using Skrollr.js in my web banner and I have a plane in the sky in the center of my banner.

At data-0 then at data-500 my plane moves from the center of the screen to the right off screen.

However when I scroll back to the top my plane moves back to data-0 but my plane is going backward.

How can I program Skrollr so that when I scroll down, my plane moves off the screen to the right but when I scroll back to the top my plane continues and comes back from the left of the screen to the center rather than going backward in motion?