A gas turbine engine comprising: a first disk ; a second disk , wherein the first disk is arranged aft of the second disk along an axis of the gas turbine engine; and a rotor arm arranged between and connecting the first disk to the second disk , wherein a cavity is defined at least between the rotor arm and the first disk , and wherein the first disk , the second disk and the rotor arm are arranged about an engine axis , characterised in that the rotor arm comprises: a radial portion having an inner diameter end and an outer diameter end ; an axial portion having a first end and a second end , wherein the first end of the axial portion is connected to the outer diameter end of the radial portion ; at least one entrance flow path defined within the radial portion extending from the inner diameter end to the outer diameter end ; and at least one exit aperture arranged proximate the second end of the axial portion , wherein a primary cooling flow is passed through the engine as a forward flowing cooling flow from aft to forward along the engine axis , wherein the at least one entrance flow path is configured to extract a portion of the primary cooling flow and direct said extracted flow into the cavity as a secondary cooling flow , wherein the secondary cooling flow is directed back to the primary cooling flow through the at least one exit aperture , and wherein the portion of the primary cooling flow that is directed to the cavity is 15- 40% of a total flow of the primary cooling flow . a first disk ; a second disk , wherein the first disk is arranged aft of the second disk along an axis of the gas turbine engine; and a rotor arm arranged between and connecting the first disk to the second disk , wherein a cavity is defined at least between the rotor arm and the first disk , and wherein the first disk , the second disk and the rotor arm are arranged about an engine axis , characterised in that the rotor arm comprises: a radial portion having an inner diameter end and an outer diameter end ; an axial portion having a first end and a second end , wherein the first end of the axial portion is connected to the outer diameter end of the radial portion ; at least one entrance flow path defined within the radial portion extending from the inner diameter end to the outer diameter end ; and at least one exit aperture arranged proximate the second end of the axial portion , a radial portion having an inner diameter end and an outer diameter end ; an axial portion having a first end and a second end , wherein the first end of the axial portion is connected to the outer diameter end of the radial portion ; at least one entrance flow path defined within the radial portion extending from the inner diameter end to the outer diameter end ; and at least one exit aperture arranged proximate the second end of the axial portion , wherein a primary cooling flow is passed through the engine as a forward flowing cooling flow from aft to forward along the engine axis , wherein the at least one entrance flow path is configured to extract a portion of the primary cooling flow and direct said extracted flow into the cavity as a secondary cooling flow , wherein the secondary cooling flow is directed back to the primary cooling flow through the at least one exit aperture , and wherein the portion of the primary cooling flow that is directed to the cavity is 15- 40% of a total flow of the primary cooling flow . <EOS>