var scrollSpeed = 20; 		// Speed in milliseconds
var step = 1; 				// How many pixels to move per step
var current = 0;			// The current pixel row
var imageWidth = 2000;		// Background image width
var headerWidth = 55;		// How wide the header is.

//The pixel row where to start a new loop
var restartPosition = +(imageWidth + headerWidth);

function scrollBg(){
//Go to next pixel row.
current += step;

//If at the end of the image, then go to the top.
if (current == restartPosition){
current = 0;
}

//Set the CSS of the plane.
$('#plane').css("background-position",current+"px 0");
}

//Calls the scrolling function repeatedly
var init = setInterval("scrollBg()", scrollSpeed);