For This trick you must be confident with the backside boardslide and backside 180. 

       First, approach the rail with speed. You must be confortable with the speed, you have. If you going too fast, you probably chicken out, and if your going too slow then the chances off you catching your edge are much greater. Next, ride up the jump and take a small hop. As your in the air you want to turn your board in a B/S 90 before you hit the rail. As your coming down spot your landing on the rail and try to land there. As you hit the rail stay right above the rail and keep your knees bent. Also, as you are sliding keep your balance centered and don't lien to far forward or backward because you will hurt your self. If, you can tell that you are going to fall it is best to fall to the side because this way you don't hurt your self as much, or if at all. Keep balanced and centered as you come cross and when you are about to come off turn your body back in F/S 90 or in another B/S 90 depending if you want to come out switch or regular. Spot your landing and try to land there. Absorb the shock with your knees are ride away clean. Good Luck!