I know the situation has changed since, but when I went to America my understanding was that a Visa Waiver was sufficient for hours building, as mattpilot said. However, I didn't have very much faith that the guy working on the immigration desk would know that, or would even understand the difference between hour building and training. And if they decide not to let you in, you're on the next plane home, with no right of appeal. If I'd had time, I'd have got a Visa, even though it wasn't necessary. Since I didn't have time, I went without one, but I certainly didn't mention to the guy on immigration that I was in the country to go flying. Especially since this was only a couple of months after September 11th.
FFF
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