Originally Posted by
kyunbit
Any idea if such high taxes/YQ exist even on UA flights within US?
It's not necessarily YQ. It could be RC, which is often miscalculated by agents, who use the value calculated on a full fare ticket instead of 0 -- this happened often with bmi's DC agent for ticket originating in Canada. Without the details of what is lumped into XT, we can't really know what is happening, but I suspect it's the case here.