A turbomachine casing assembly including an inner casing element for arrangement radially outward of a turbomachine fan; an outer casing element for arrangement radially further outward of the turbomachine fan; a retaining lip arranged radially inward of a portion of the inner casing element; and a separator extending between the inner and outer casing elements and arranged to urge a portion of the inner casing element against the lip. The separator is arranged in compression between the inner and outer casing elements to urge the portion of the inner casing element against the lip. The separator is arranged to engage a frangible region of the inner casing element such that the frangible region is configured to break in response to an impact satisfying predetermined conditions, allowing the inner casing element to displace radially outwards exposing features to improve retention of a released fan blade.