When I use my airless sprayer the pattern has two heavy paint lines on the outer edges of the spray pattern.
This is caused by either a worn out tip, the paint to too heavy (thick) for your tip size or not enough pressure. First, try increasing the pressure to see if this helps. If it does, you can thin or condition your paint for a better spray pattern.
Replace the spray tip if it is old and <a href="http://www.house-painting-info.com/spray-tip.html">choose a airless spray tip</a> that will work with the coating your spraying. Thicker materials need a larger tip size.