A functional unit in a passenger cabin includes a support unit and a passenger seat system. The passenger seat system is formed in two parts and has an upper constructional unit and a lower constructional unit that are each separate components, the upper constructional unit arranged on the support unit and containing at least one backrest, and the lower constructional unit containing a seat frame, at least one seat element and restraint for the passenger on the seat. The seat frame is fastenable to seat rails on the floor of a passenger cabin. For the use position, the upper and lower constructional units are positioned such that a passenger seat is formed. In the use position, personal comfort for the individuals on the seats is not impaired as far as possible, and the division of the seat system into two parts cannot be seen by the user.