This pack can be used as a carry on if it is not completely full. This pack when filled definitely will not meet the size requirements. I've taken this pack as a carry on when it was half full. I simply folded it in half.
I have this same size backpack and i took t with me when i traveled to mexico and i had no problem getting it in to the plane. i guess it ll depends on where you are traveling to because they might have different regulations.
I have a smaller one, the 35+10L, which has barely passed the carry on requirements a few times. If this bag were packed full it probably would have to be checked. If it weren't full and you took the top section off you might be able to.