Originally Posted by mbeach
Those plastic sliders were add-ons, like the strap to hold up the back seat. It's another case of engineering coming to the rescue of bad design -our seats are too wide for the cabin. The sliders were put there to prevent the male portion of the buckle from getting slammed in the door -however, they only work for fat people or short people.
The plastic slider needs to be moved if you want to pull the horizontal portion of the belt tight. If you are skinny, or you have the seat all the way back, there's not enough slack on the belt to position that slider in the right place to locate the buckle when the belt is fastened AND when the belt is off.