recovery is addressed by removal of the boundary layer (at the ramp bleed slot) and suitable shaping of the subsonic diffuser leading to the engine. The high pressure recovery for the Concorde intake at cruise gave an intake pressure ratio of 7.3:1. Shock waves gave rise to excessive boundary-layer growth on the front ramp. The boundary layer was removed through the ramp bleed slot and bypassed the subsonic diffuser and engine, where it would otherwise have caused excessive duct loss and unacceptable distortion at the engine. Since the ramp bleed slot was in the subsonic diffuser, and downstream of the shock system, changes in flow demanded by the engine would be accommodated with corresponding changes in the bleed slot flow without significantly affecting the external shock pattern. Engine flow reductions caused by throttling or shutting down were dealt with by dump-door opening. The dump doors were closed at cruise to prevent loss in thrust, since air leaking from the duct does not contribute to the pressure recovery in the intake. At take-off, since the intake area was dimensioned for cruise, an auxiliary inlet was required to meet the higher engine flow. Distortion of the flow at the engine face also had to be addressed, leading to an aerodynamic cascade with the auxiliary door. Forces from the internal airflow on the intake structure are rearward (drag) on the initial converging section, where the supersonic deceleration takes place, and forward on the diverging duct where subsonic deceleration takes place up to the engine entry. The sum of the 2 forces at cruise gave the 63% thrust contribution from the intake part of the propulsion system. In order to achieve the necessary accuracy in the control of the intake ramp and spill positioning, it was found necessary to use a digital signal processor in the Air Intake Control Units. This was developed relatively late in the program (~1972) by the Electronics and Space Systems division of the British Aircraft Corporation at Filton, Bristol. The Air Intake Control Units ensured the required fuel-economy for transatlantic flights. The digital processor also accurately calculated the necessary engine-speed scheduling to ensure an adequate surge margin under all engine and airframe operating conditions. Concorde's Air Intake Control System also pioneered the use of digital data highways (multiplexed serial data buses) which connected the Air Intake Sensor Units that collected aerodynamic data at the nose of the aircraft (total