ENGINE AIR INTAKES
Each engine air intake is basically rectangular in cross section with a moveable ramp in the roof and spill door in the floor.
Hydraulic actuators position the ramp to vary the intake capture area and open the spill door to augment the spill of unwanted air.
At take off and low speeds an auxiliary inlet vane, integral with the spill door, provides extra air to the engine. This vane is operated by differential pressure only. During operation of the spill door the vane is locked in the closed position.
A perforated bleed through the lower surface of the intake aids inlet performance at high Mach numbers. The flow through this bleed is limited by the exit cross section only and is not mechanically controlled.

OPERATION
At speeds below M=1.3 the ramps remain fully up and the spill doors closed. At speeds above M=1.3 the ramps and spill doors are positioned between scheduled maximum and minimum angular positions determined by the prevailing control parameters, namely intake pressure ratio, Mach number, engine speed N1 angle of attack and actual ramp and spill door
positions. The change in ramp angle varies the intake capture area, controls the fore spillage of air and creates a shockwave system originating at the ramp angle. This shockwave system slows the air entering the intake to approximately M=0.5. In the optimum configuration at any Mach number the ramp is positioned to cause the shockwaves to converge on the lower lip
of the floor.
When the predetermined scheduled ramp angle is reached any excess air entering the intakes (e.g. during very high ambient temperatures or during throttling) is dumped through the spill door. In addition, as the angle of the spill door increases the
scheduled maximum ramp angle is increased by an incremental function of the spill door angle.