A turbomachine casing assembly (100;200;300), comprising: a first casing element (110;210;310) located radially outward of one or more rotating aerofoil elements of a turbomachine; a second casing element located radially outward of the first casing element (110;210;310); and a void, provided between the first casing element (110;210;310) and the second casing element, at a first end of the first casing element (110;210;310); wherein the first end (112;212;312) of the first casing element (110;210;310) is located against a corresponding first end of the second casing element by an energy absorbing element, and the first casing element (110;210;310) comprises a cantilever, the cantilever being arranged in a region extending along the first casing element (110;210;310) from the first end and having a pivot axis at a mid portion of the first casing element (110;210;310); whereby upon release of one of the rotating aerofoil elements, the cantilever bends into the void provided between the first and second casing elements(110;210;310,120), which causes the energy absorbing element (140;142;230;340) to deform and to thereby absorb at least some of the impact energy resulting from the released rotating aerofoil element; wherein a radially distal face (116;216;316) of the first casing element (110;210;310) is angled relative to a radially proximal face of the second casing element, such that the void is provided therebetween; the radially distal face (116;216;316) of the first casing element (110;210;310) comprises a slit, the slit being disposed along the pivot axis on the radially distal face (116;216;316) of the first casing element (110;210;310) and extending substantially through a core of the first casing element (110;210;310); characterised in that the slit comprises a linear plurality of apertures extending along the cantilever pivot axis on the radially distal face (116;216;316) of the first casing element (110;210;310). a first casing element (110;210;310) located radially outward of one or more rotating aerofoil elements of a turbomachine; a second casing element located radially outward of the first casing element (110;210;310); and a void, provided between the first casing element (110;210;310) and the second casing element, at a first end of the first casing element (110;210;310); wherein the first end (112;212;312) of the first casing element (110;210;310) is located against a corresponding first end of the second casing element by an energy absorbing element, and the first casing element (110;210;310) comprises a cantilever, the cantilever being arranged in a region extending along the first casing element (110;210;310) from the first end and having a pivot axis at a mid portion of the first casing element (110;210;310); whereby upon release of one of the rotating aerofoil elements, the cantilever bends into the void provided between the first and second casing elements(110;210;310,120), which causes the energy absorbing element (140;142;230;340) to deform and to thereby absorb at least some of the impact energy resulting from the released rotating aerofoil element; wherein a radially distal face (116;216;316) of the first casing element (110;210;310) is angled relative to a radially proximal face of the second casing element, such that the void is provided therebetween; the radially distal face (116;216;316) of the first casing element (110;210;310) comprises a slit, the slit being disposed along the pivot axis on the radially distal face (116;216;316) of the first casing element (110;210;310) and extending substantially through a core of the first casing element (110;210;310); characterised in that the slit comprises a linear plurality of apertures extending along the cantilever pivot axis on the radially distal face (116;216;316) of the first casing element (110;210;310).