Abstract: An aircraft, preferably a large capacity passenger aircraft with two passenger decks, has a double-T tail assembly arranged on its tail section. The double-T tail assembly includes a double fin and rudder assembly and a tailplane and elevator assembly, and provides a significant increase in the usable passenger cabin space in the tail section of the aircraft. The double fin and rudder assembly has a U-shaped structure and comprises two upright stabilizer fins connected to each other by a horizontal torsion box that fixedly extends crosswise through the fuselage tail section within the floor of a cabin deck. The tailplane and elevator assembly is pivotably mounted on the upper tips of the two upright stabilizer fins in a double-T arrangement.