Though there are some definate advantages to riding the plane in uniform, getting through security is always a bit of a hassle. The metal rivets in your combat boots will set off alarms, and I know people who have been forced to dress down as result. Your joining instructions for course may demand being in uniform, but there will always be a time and place for changing attire.
Kernewek
P.S. If they say casual business attire, by all means dress so. However, I've only ever seen casual civilian or uniform in this sort of travel (regardless of brigade or area) - so if you haven't a suit, I'd not be worried too much.