I can tip it toward the seat back--which is normal, except that once it is back toward the seat back, there is so much slack in the belt that it doesn't seem locked anymore, and I can then tilt it sideways. Hard to describe, but really doesn't seem as secure as it does with just a lap belt.
I am concerned because I am flying alone with my infant next week and I am really concerned about installing the seat in my mom's car when she picks me up at the airport. I don't want to haul the base too b/c I would have to carry it with me and all my other stuff (and baby) through the airport. I am only allowed to check one bag. Plus, mom's car doesn't have latch so i would need to practice installing the base with the belt (hubby has done that for our cars). (mom's car has three shoulder belts in the rear seat of her car--older Camry).