Noise attenuation panel

An aeroengine having an engine core and a nacelle structure surrounding the core and defining a fan duct having inner and outer fan duct walls, wherein one or each of the fan duct walls is formed by or includes a noise attenuation panel, the noise attenuation panel comprises:

• a cellular component part having a front face, a rear face and a structure which defines a multiplicity of cells between the front face and the rear face;
• a facing component part which:
• has a front face and a rear face;
• extends across the ends of the cells of the cellular component part at the front face thereof;
• with the rear face of the facing component part adjacent the front face of the cellular component part, and
• is provided with a multiplicity of holes which extend through the facing component part from the front face to the rear face to provide gaseous fluid communication between the cells of the cellular component part and the front face of the facing component part for the attenuation of noise generated by gaseous fluid flow over the surface of the front face of the facing component part;
• characterized in that:
• each of the multiplicity of holes in the facing component part has a bore diameter which increases along the bore in the direction of the rear face of the facing component part through the bore or at least a part or parts of the bore and which does not at any point of the bore decrease along the bore in the direction of the rear face of the facing component part.