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.