Originally Posted by
tkamp
... and then the higher tier from Economy to Business.
Upgrade priority:
1. IO passengers
2. Platinum passagers (Flex Plus, Flex, Saver, Special)
3. Flex Plus passengers (Gold, Silver)
4. Flex passengers (Gold, Silver)
5. Saver passengers (Gold, Silver)
So it's mainly based on highest priced tickets rather than status to the dismal of many frequent flyers.
Other than that, yes, you are right: Eco > Prem; Prem > Bus; Bus > First.