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.