Mach 2.02 (~2,154 km/h or 1,338 mph) cruising speed[72] for optimum fuel consumption (supersonic drag minimum and turbojet engines are more efficient at higher speed[73]) Fuel consumption at Mach 2 (2,120 km/h; 1,320 mph) and at altitude of 60,000 feet (18,000 m) was 4,800 US gallons per hour (18,000 L/h).[74] Mainly aluminium construction using a high temperature alloy similar to that developed for aero-engine pistons.[75] This material gave low weight and allowed conventional manufacture (higher speeds would have ruled out aluminium)[76] Full-regime autopilot and autothrottle[77] allowing "hands off" control of the aircraft from climb out to landing Fully electrically controlled analogue fly-by-wire flight controls systems[68] High-pressure hydraulic system using 28 MPa (4,100 psi) for lighter hydraulic components,[78] tripled independent systems ("Blue", "Green", and "Yellow") for redundancy, with an emergency ram air turbine (RAT) stored in the port-inner elevon jack fairing supplying "Green" and "Yellow" as backup.[79] Complex air data computer (ADC) for the automated monitoring and transmission of aerodynamic measurements (total pressure, static pressure, angle of attack, side-slip).[80] Fully electrically controlled analogue brake-by-wire system[81] Pitch trim by shifting fuel fore-and-aft for centre-of-gravity (CoG) control at the approach to Mach 1 and above with no drag penalty.[82] Pitch trimming by fuel transfer had been used since 1958 on the B-58 supersonic bomber.[83] Parts made using "sculpture milling", reducing the part count while saving weight and adding strength.[84] No auxiliary power unit, as Concorde would only visit large airports where ground air start carts are available.[85]