i ran a few searches but couldn't find the answer to this question but i am also quickly skimming because i am in such a panic so please forgive me if this has already been answered somewhere. we are traveling by air on thursday and i just got my ridesafer vest today. i bought it for my 4.5 yr old ds who weighs 42 lbs. i understand how to install in a car but i'm completely confused about how this would be fit on an airplane since the top tether cannot be used. is it enough just to use the lap belt with this vest? it seems to me then that he has no chest protection. am i missing something??? please help! i'm in panic mode because we are leaving on thursday and i already will be lugging one marathon for younger ds and the thought of this vest not working on the plane and having to carry 2 marathons is freaking me out!!! tia for helping and please forgive my frantic state.