A gas turbine engine turbine vane airfoil comprising: an article wall having an inner portion at least partially defining a cavity and an outer portion ; a plurality of first cooling passage networks (76; 76-1; 76-3) each defining first dimensions and embedded in the article wall between the inner portion and the outer portion of the article wall ; and a plurality of second cooling passage networks (76; 76-2; 76-4) each defining second dimensions and embedded into the article wall between the inner portion and the outer portion of the article wall , wherein the plurality of first and second cooling passage networks (76; 76-1, 76-2; 76-3, 76-4) are arranged in one of a first column (90; 98) of radially positioned networks (76; 76-1; 76-3, 76-4) and a second column (92; 100) of radially positioned networks (76; 76-2; 76-3, 76-4), wherein each of the first cooling passage networks (76-1; 76-3; 76-4) have an outlet orifice (77-1; 77-3; 77-4) radially aligned with a second mid-span wall (94; 102; 104) between adjacent networks (76; 76-2; 76-3; 76-4) in the second column (92; 100); characterised by comprising a plurality of cooling holes (97; 106) located upstream of the first column (90; 98) of radially positioned networks (76; 76-1; 76-3, 76-3) and radially aligned with at least one first mid-span wall (96; 108, 110) between adjacent networks (76; 76-1; 76-3, 76-4) in the first column (90; 98) of networks (76; 76-1; 76-3, 76-4), wherein the airfoil is sized such that it cannot accommodate an additional column of cooling passage networks upstream of the first cooling passage networks (76; 76-2; 76-3; 76-4). an article wall having an inner portion at least partially defining a cavity and an outer portion ; a plurality of first cooling passage networks (76; 76-1; 76-3) each defining first dimensions and embedded in the article wall between the inner portion and the outer portion of the article wall ; and a plurality of second cooling passage networks (76; 76-2; 76-4) each defining second dimensions and embedded into the article wall between the inner portion and the outer portion of the article wall , wherein the plurality of first and second cooling passage networks (76; 76-1, 76-2; 76-3, 76-4) are arranged in one of a first column (90; 98) of radially positioned networks (76; 76-1; 76-3, 76-4) and a second column (92; 100) of radially positioned networks (76; 76-2; 76-3, 76-4), wherein each of the first cooling passage networks (76-1; 76-3; 76-4) have an outlet orifice (77-1; 77-3; 77-4) radially aligned with a second mid-span wall (94; 102; 104) between adjacent networks (76; 76-2; 76-3; 76-4) in the second column (92; 100); characterised by comprising a plurality of cooling holes (97; 106) located upstream of the first column (90; 98) of radially positioned networks (76; 76-1; 76-3, 76-3) and radially aligned with at least one first mid-span wall (96; 108, 110) between adjacent networks (76; 76-1; 76-3, 76-4) in the first column (90; 98) of networks (76; 76-1; 76-3, 76-4), wherein the airfoil is sized such that it cannot accommodate an additional column of cooling passage networks upstream of the first cooling passage networks (76; 76-2; 76-3; 76-4). <EOS>