This is quite a hard trick and you should feel REALLY comfortable with doing heelflips and catching them. Come up to your target just like a regular F/S Boardslide except your feet in Heelflip position. Pop a huge Heelflip and get over top of the rail. Spin it quick and make sure you catch it in time, if not you might land dark slide or something and bail. This getting on part takes a lot of confidence, you will probably be taking lots of tries just heelflipping the board so it gets on. First you might want to try this wearing pads, if you don't want to or have any then try to set your rail up onto grass, so that way you don't fall as hard. Keep trying to get on until once in a while you can do it. Once you land bend your knees, but not too much or too little because you will slip out and bail. Getting off is just like a regular F/S Boardslide. Tips: bend down a lot and pop very hard, this way your heelflip will get over top of the rail. Make sure you can B/S Heelflip really well, it helps as you are spinning a 90 B/S Heel to get on. Read the trick tip on a B/S Heelflip, that might help you. Make sure that once you commit you commit 100% if you commit then quit just after you caught the board or something it's very likely you will bail. When you are spinning the 90 Heelflip make sure your body (look at your shoulders to check) is parallel with your board at all times in the trick and 90 to the rail when you land on the boardslide.