My limited experience has led me to check a tripod. In the past, I often carried a small Gitzo on to the plane and never had a problem. Last year I took the tripod to Osaka, on the return flight, I was not allowed to board with the tripod. I checked the tripod and upon my arrival in Chicago had to wait 2 hours for the tripod to clear agricultural inspection. When I returned home, I realized the entire ball head had been disassembled (and not reassembled very well). I’m sure the tripod drew attention as an unpacked item. The decisions of airport security seem arbitrary and so the safer mode is checked.