shown in fig6 the line of failure 40 cuts across the passages 34 the compressed gas in the passages 34 is as shown by the arrows x and y the release of the compressed gas imparts a force shown by the arrow a to displace the radially outer first portion 36 in the direction of the arrow a away from the trailing blades on the fan 12 fig7 to 9 show a further embodiment in which the mounting support 32 of the fan blade assembly 22 is provided with a region of weakness 42 adjacent the platform 32 the region of weakness is in the form of a fuse the region of weakness 42 is provided on the leading edge 43 of the aerofoil member 30 at the radially end region of the aerofoil member 30 adjacent the platform 32 when the aerofoil member 22 is struck by an object the aerofoil member 30 fails at the region of weakness 42 as shown in fig8 a line of failure 44 extends part way across the aerofoil member 30 of the blade assembly 22 the center of gravity g of the aerofoil member 22 is such that the radially outer first portion 36 rolls rearwardly as shown by the arrow b thereby increasing the length of the line of failure 44 this rearward rolling of the first portion 36 continues until the first portion 36 becomes completely detached from the second portion 38 and is displaced from a rearward direction from the fan 12 away from the other blades 22 as shown in fig9 thus in this embodiment the center of gravity is such that it has a tendency to pull the failing first portion 36 of the main body 22.