A fixed-shell aircraft passenger seat including a seat bottom pivotably attached to a seatback, a fixed-shell positioned behind the seatback, left and right spreaders guiding the seat bottom forward and lower as the seat bottom moves to a reclined sitting position, a linkage arm linked with movement of the seat bottom, and a locking gas spring arranged between the linkage arm and a fixed seat frame member for counterbalancing passenger weight to return the seat bottom to upright and prevent over acceleration into a cradle recline sitting position.