a passenger seat having a walk - over seat back mounted for movement on a pair of rotatable shafts through a pair of of levers mounted on each end of the shafts . the levers contact each other at opposite seat positions to support the seat back . the pair of shafts include a torsion section at each end portion capable of undergoing plastic deformation upon a lock mechanism detecting predetermined deceleration forces . a lever and link element are operatively connected between the seat cushion frame to permit movement . the seat cushion is removable secured to the seat cushion frame .