var transparent = null;

function doMove() {
    var position = parseInt(transparent.style.backgroundPosition);
    (position >= -354) ? position -= 1 : position = 450;
    transparent.style.backgroundPosition = position + 'px';
    setTimeout (doMove, 10);
}

function init() {
  transparent = document.getElementById('plane');
  transparent.style.backgroundPosition = '-500px';
  doMove();
}


window.onload = init;