In Alabama, what triggers the state tax folks to spring into action is the assignment of an N number (registration) to your airplane. Apparently the FAA notifies them. My state tax folks wanted me to pay sales tax for what I paid for it (that's before I told them I was building it), and failing that, on every component that was bought out of state, declare it each year, and pay taxes on it as I go. The county tax folks quickly appeared as well, wanting me to pay property tax on my wonderful new airplane. They eventually consented to me paying taxes on what it's worth at the moment, and expect me to increment its value every year. I guess I'm lucky they don't charge me taxes for the luxury of having a TIG welder...
Mark Langford, Huntsville, Alabama N56ML "at" hiwaay.net see KR2S project at http://home.hiwaay.net/~langford