An assembly including a plurality of seats (10a, 10b, 10c) arranged in a row along a longitudinal axis X, each seat including an armchair (11a, 11b, 11c) and a lateral box (12a, 12b, 12c) arranged laterally to said armchair, in which assembly: each armchair has a front side oriented substantially in the same direction; the armchairs, on the one hand, and the lateral boxes, on the other hand, are arranged in a staggered manner in two rows parallel to the longitudinal axis X, each seat including a covering shell determining a rear surface in a rear zone of the armchair and determining a front surface in a front zone of the lateral box, a space between a rear surface of a front seat and a front surface of a rear seat, located immediately behind said front seat in the assembly, forming a passage for an occupant of said rear seat, characterized in that: - in a section formed in a vertical plane in which there is a minimum width Lmin of the passage, the rear surface and the front surface have convex profiles facing each other, a width L(hz) of said passage in said vertical plane increasing continuously in the direction of the heights hz, above a reference cabin floor, decreasing from a height hzmin of the minimum width Lmin, at least up to the vicinity of the floor, and said width L(hz) increasing continuously in the direction of the increasing heights hz from said height hzmin of the minimum width Lmin, such that the width L(hz) has a single point of change in the direction of variation (hzmin, Lmin); - the rear surface has a convex shape in sections along horizontal planes, giving, combined with the convex profiles in a section along a vertical plane, to said rear surface a pseudo-ellipsoidal cap shape; - the front surface in a front zone of the lateral box (12a, 12b, 12c) has a substantially straight shape in sections along horizontal planes, giving to said front surface a partial cylinder shape with substantially horizontal axis and generators; - the rear surface of the front seat and the front surface of the rear seat giving the passage a convergent-divergent shape with a neck of width Lmin guiding a user of the seat. - in a section formed in a vertical plane in which there is a minimum width Lmin of the passage, the rear surface and the front surface have convex profiles facing each other, a width L(hz) of said passage in said vertical plane increasing continuously in the direction of the heights hz, above a reference cabin floor, decreasing from a height hzmin of the minimum width Lmin, at least up to the vicinity of the floor, and said width L(hz) increasing continuously in the direction of the increasing heights hz from said height hzmin of the minimum width Lmin, such that the width L(hz) has a single point of change in the direction of variation (hzmin, Lmin); - the rear surface has a convex shape in sections along horizontal planes, giving, combined with the convex profiles in a section along a vertical plane, to said rear surface a pseudo-ellipsoidal cap shape; - the front surface in a front zone of the lateral box (12a, 12b, 12c) has a substantially straight shape in sections along horizontal planes, giving to said front surface a partial cylinder shape with substantially horizontal axis and generators; - the rear surface of the front seat and the front surface of the rear seat giving the passage a convergent-divergent shape with a neck of width Lmin guiding a user of the seat.