1. Seating system for passenger service vehicles, for aircraft in particular2. In a seating system for passenger service vehicles, for aircraft in particular, having a plurality of seats mounted side by side for the purpose of forming a row of seats which are limited laterally by the arm rests (13) determining the seat width, at least one of which arm rests is operated in conjunction with an adjoining arm rest (13) on a seat positioned beside it for the purpose of adjustment in the transverse direction of the seat to positions which correspond to different seat widths, by means of an adjustment mechanism having lever gearing with two articulated levers (21) having a parallelogram guide, each levers (21) being mounted on one side on pivot axes (23) positioned on the bearing structure (5) of the seat row and on the other side on pivot axes (25) connected to the arm rest (13), the pivot axes (23, 25) being positioned in parallel with each other and separated by the same distances from each other for the purpose of forming the parallelogram, the pivot axes (23, 25) of the parallelogram guide extending in the longitudinal direction of the seat and at least in approximation horizontally in relation the standard installed position of the seat row.