The QX internal site claims the preference was to add a 6th SEA-BLI flight but that aircraft schedules didn't permit an opening for it. But an aircraft sits in PDX long enough to make it work. So when it is over at the end of the summer, there will be a 6th daily flight added to SEA-BLI.

It says this aicraft originates in BUR and goes thru PDX to BLI and going back it ends in SMF.