A European consortium is evaluating materials for the construction of a new supersonic transport aircraft that may replace Concorde. Current designs propose to use an aluminium alloy for the fuselage which is required to have superior creep resistance and damage tolerance to the Concorde alloy 2618A. Promising results have been obtained with extruded Al-Cu alloys containing minor additions of magnesium and silver which stimulate hardening by the relatively stable S2 precipitate. The proposed alloys have tensile and accelerated creep properties which are better than those of competing commercial alloys of the 2000 series, together with satisfactory levels of fracture toughness. Of the four experimental alloys studied, the optimal composition is Al-(5.6)Cu-(0.45)Mg-(0.45)Ag-(0.30)Mn-(0.18)Zr (wt-%). Tensile properties of the Al-Cu-Mg-Ag alloy extrusions measured at 20 deg C exceed those of the commer-cial Al-Cu and Al-Cu-Mg alloys of the 2000 series. For example, the longitudinal properties of the thick (276 mm) Al-Cu-Mg-Ag extrusions with the higher copper contents of 5.6 % and 6.5 % aged to the T6 temper, averaged as follows: 0 % to 2 % proof stress is 471 MPa, tensile stress is 522 MPa, and per cent elongation is 10.1 %. Tensile properties for the experimental alloys with 4.5 % and 3.4 %Cu were lower and fell within the upper and midranges of those for the 2000 series alloys at 20 deg C. Fracture toughness values for each of the four Al-Cu- Mg-Ag alloys exceeded the minimum requirements for high strength aluminium alloys in the longitudinal, long transverse, and short transverse directions. These values increased as the copper content was reduced. The average fracture toughness for the thick (276 mm) extrusions with 5.6 % Cu (longitudinal 39.5 MPa.mexp 0.5), long transverse 28.9 MPa.m^0.5, and short transverse 26.0 MPa.m^0.5 were significantly higher than values for alloy with 6.5 % Cu. Accelerated creep tests at 150 deg C and 180 deg C indicated that the performance of the extruded Al-Cu-Mg-Ag alloys with 5.6 % and 6.5 % Cu was clearly superior to that of the 2000 series alloys.