and were each driven by a single-stage turbine. Due to the high inlet air temperatures at Mach 2 cruise - in excess of 120 degrees C - the compressor drums and blades were made from titanium except for the last 4 HP stages, which were Nimonic 90 nickel alloy. Nickel alloys were normally only required in the hotter turbine areas, but the high temperatures that occur in the last stages of the compressor at supersonic flight speeds dictated its use in the compressor also. The HP turbine stator and rotor blades and LP turbine rotor blades were cooled. A partial reheat (20% thrust boost) was installed to give the required take-off thrust. It was also used for transonic acceleration from Mach 0.95 up to Mach 1.7; the aircraft flew supersonically without reheat above that speed, and at cruise the engine contributed 8% of the thrust produced by the complete propulsion system. All major components of the 593 were designed for a life of 25,000 hours, with the exception of the compressor and turbine blades, which were designed for a 10,000 l-hour life. An engine installed on Concorde could be changed in one hour, 50 minutes. Intake The Concorde's variable-geometry intake, designed by BAC, like any jet-engine intake, has to deliver the air to the engine at as high pressure as possible (pressure recovery) and with a pressure distribution (distortion) that can be tolerated by the compressor. Poor pressure recovery is an unacceptable loss for the intake compression process, and unacceptable distortion causes engine surging (from loss of surge margin). If the engine is an afterburning turbojet, the intake also has to supply cooling air for the hot afterburner duct and engine nozzle. Meeting all the above requirements over the relevant parts of the operating envelope was vital for Concorde to become a viable commercial aircraft. They were met with variable geometry and an intake-control system that did not compromise the operation of the engine nor the control of the aircraft. Supersonic pressure recovery is addressed by the number of shock waves that are generated by the intake: the greater the number, the higher the pressure recovery. Supersonic flow is compressed or slowed by changes in direction. The Concorde intake front ramps changed the flow direction, causing oblique external shocks and isentropic compression in the supersonic flow. The TSR-2 had used a half-cone translating centre-body to change the direction. Subsonic pressure