pressure turbine 16 via a second shaft 20 finally the high pressure compressor 13 is driven by the high pressure turbine 15 via a third shaft 21 the first second and third shafts 19 20 and 21 are concentric during the operation of the engine 10 air initially compressed by the fan 11 is divided into two flows the first and major flow is exhausted directly from the engine 10 to provide propulsive thrust the second flow is directed into the intermediate pressure compressor 12 and high pressure compressor 13 where further compression takes place the compressed air is then directed into the combustion equipment 14 where it is mixed with fuel and combustion takes place the resultant combustion products then expand through and thereby drive the high intermediate and low pressure turbines 15 16 and 17 before being exhausted through the nozzle 18 to provide additional propulsive thrust the low pressure turbine 17 comprises three axially spaced apart annular arrays of rotor aerofoil blades 22 the aerofoil blades 25 are mounted for rotation about the longitudinal 26 axis of the engine 10 on discs not shown in the conventional manner the rotor aerofoil blades 22 are enclosed by the low pressure turbine casing 27 the low pressure turbine casing 27 is in turn partially enclosed by a lightweight annular support member 28 which can be seen more easily if.