A thrust reverser of a propulsion system nacelle, the thrust reverser extending circumferentially about a lengthwise-extending centerline, the thrust reverser comprising: a lengthwise-extending upper track beam; a lengthwise-extending lower track beam; an annular torque box extending circumferentially between the upper and lower track beams (44,46); an annular cascade array extending circumferentially between the upper and lower track beams (44,46); wherein the cascade array is circumferentially segmented into a plurality of cascade portions; and wherein at least one of the plurality of cascade portions is made at least substantially of cast aluminium that permits the at least one cascade portion to bear high loads during both a forward thrust operation of the thrust reverser and a thrust reversing operation of the thrust reverser; characterised in that the plurality of cascade portions include: a first corner cascade portion disposed adjacent to and connected to the upper track beam; a second corner cascade portion disposed adjacent to and connected to the lower track beam; an intermediate cascade portion disposed circumferentially between the first and second corner cascade portions; wherein the first and second corner cascade portions are made at least substantially of a cast aluminium that permits the first and second corner cascade portions to bear high loads during both a forward thrust operation of the thrust reverser and a thrust reversing operation of the thrust reverser; and wherein the intermediate cascade portion is made at least substantially of a composite material that permits the intermediate cascade portion to bear high loads only during a thrust reversing operation of the thrust reverser. a lengthwise-extending upper track beam; a lengthwise-extending lower track beam; an annular torque box extending circumferentially between the upper and lower track beams (44,46); an annular cascade array extending circumferentially between the upper and lower track beams (44,46); wherein the cascade array is circumferentially segmented into a plurality of cascade portions; and wherein at least one of the plurality of cascade portions is made at least substantially of cast aluminium that permits the at least one cascade portion to bear high loads during both a forward thrust operation of the thrust reverser and a thrust reversing operation of the thrust reverser; characterised in that the plurality of cascade portions include: a first corner cascade portion disposed adjacent to and connected to the upper track beam; a second corner cascade portion disposed adjacent to and connected to the lower track beam; an intermediate cascade portion disposed circumferentially between the first and second corner cascade portions; wherein the first and second corner cascade portions are made at least substantially of a cast aluminium that permits the first and second corner cascade portions to bear high loads during both a forward thrust operation of the thrust reverser and a thrust reversing operation of the thrust reverser; and wherein the intermediate cascade portion is made at least substantially of a composite material that permits the intermediate cascade portion to bear high loads only during a thrust reversing operation of the thrust reverser. a first corner cascade portion disposed adjacent to and connected to the upper track beam; a second corner cascade portion disposed adjacent to and connected to the lower track beam; an intermediate cascade portion disposed circumferentially between the first and second corner cascade portions; wherein the first and second corner cascade portions are made at least substantially of a cast aluminium that permits the first and second corner cascade portions to bear high loads during both a forward thrust operation of the thrust reverser and a thrust reversing operation of the thrust reverser; and wherein the intermediate cascade portion is made at least substantially of a composite material that permits the intermediate cascade portion to bear high loads only during a thrust reversing operation of the thrust reverser.