A book I have called Muay Thai Basics by Cristoph Delp that shows this and many of the other "flying" techniques in step by step detail, but explains that you will rarely ever see them in professional matches anymore as they require a lot of energy and are easily blocked by those with experience. Additionally, this move specifically requires the attacker to step up on the thigh of the opponent. In past days this was easier to accomplish as fighters' stances were commonly in a crouch, as opposed to standing more upright as has been found to be more effective and practiced these days. Thus, if the opponent is not in a crouch, stepping up on their thigh will be rather difficult, unless your opponent lacks experience and places themselves in a position it can be pulled off. It goes on to say that moves such as these are commonly shown in demonstrations due to their entertainment value however. Here's a link for that book, it doesn't compare to actual training in any way, but it does make for a good read when you can't train.
http://www.amazon.com/Muay-Thai-Basics-Introductory-Techniques/dp/1583941401