Hi Arno, I'm working with siamavsim to modify VTBS2006. I have read all about ActiveGate and CAT tool. I'm working to modify the gate and catagorize into 3 different hights for different models of aircraft. I modified the previous gate to more moving parts like in tutorial downloaded from AVSIM. The question is what should I do before I complie with FS2004 SDK after I've got *.MDL and *.XML. I found no *.asm or *0.asm. Second question, after I modify the *.asm what should I do next. Do I have to complie the sameway I did with other Gmax model? The third question is what the different is between active gate and CAT tool. Which one is prefered for some kind of animation? I guess the active gate is just for the gate and CAT tool is for other animations such as opening hangar gate. Quit a bit confusing for newbies. Best Regards, Jirayu Tanabodee P.S. It would be nice if you have some flow chart what is all the process where to stop where to modify.