An aircraft comprising a fuselage (1) subdivided by a floor (2) into a top volume (3) and a bottom value (4) in which girders (5) extend supporting the floor and co-operating with the fuselage and the floor to define two lateral housings (6) that are of substantially triangular cross-section and that extend parallel to a longitudinal axis of the fuselage. Calculation units (100) are arranged in the lateral housings and each comprises a box (101) defining a main compartment containing calculation modules (122) insertable into the main compartment along an insertion axis through an opening in the compartment and connectable to the connectors (115) carried by a back wall (116) of the compartment so as to extend into the main compartment opposite from the opening, the insertion axis being substantially parallel to the longitudinal axis of the fuselage.