In UK, I believe the 3 inch non-locking rule applies to "on or about your person"... That apart, how would you propose to get a fixed blade through airport (I assume) security, and onto the 'plane in a backpack ??? I ask this because I have successfully brought various "offensive" items from UK., but this has always been in a suitcase (hold baggage).
All the best with the trip, and look me up if you're in this neck of the woods (I'll lend you one !!?@?!!)