order to allow the maximum airflow into the engine if necessary this ensures that the efficiency of the engine is maximised at all times and that the flow of air into the inlet is not jeopardised when the blades are not required preferably when they are not required the blades 10 are fully retracted and lie flush with the wall of the engine containment bay 4 when required the blades 10 can then be moved into a position for shearing the airflow this configuration also allows the blades 10 to be partially retracted or moved in order to create the most optimum position for shearing the airflow retraction of the blades 10 may be towards the low pressure fan or towards the containment bay 4 it is also envisaged that each of the blades 10 is capable of being moved closer to or further away from the low pressure fan in both circumstances it is envisaged that ingested air is used to move the blades 10 towards the fan or to retract the blades and power is only used to move the blades further away from the fan or to engage the blades 10 from their retracted position at fig1 there is shown a blade 10 in cross section the blade comprises a wall 50 and a cavity 52 which may run along all or part of the said blade 10 the cavity 52 may advantageous comprise conductive materials suitable for passing electricity through which may be.