A gas turbine engine comprising: at least one blade outer air seal including a wall portion having a first side and a second side; and a plurality of cooling passages extending between the first side of the wall portion and the second side of the wall portion comprising: a plurality of inlets located on the first side of the wall portion at a first axial position, the plurality of inlets having a constant axial position relative to an axis of the engine; and a plurality of outlets located on a second side of the wall portion, wherein the plurality of outlets include a first plurality of outlets located axially upstream from a second plurality of outlets, characterised in that: the plurality of passages comprises alternating forward passages including an axially upstream directional component in addition to a circumferential component and aft passages including an axially downstream directional component in addition to a circumferential component; and the plurality of inlets are connected to corresponding ones of the first plurality of outlets by the forward passages and to corresponding ones of the second plurality of outlets by the aft passages. at least one blade outer air seal including a wall portion having a first side and a second side; and a plurality of cooling passages extending between the first side of the wall portion and the second side of the wall portion comprising: a plurality of inlets located on the first side of the wall portion at a first axial position, the plurality of inlets having a constant axial position relative to an axis of the engine; and a plurality of outlets located on a second side of the wall portion, wherein the plurality of outlets include a first plurality of outlets located axially upstream from a second plurality of outlets, characterised in that: the plurality of passages comprises alternating forward passages including an axially upstream directional component in addition to a circumferential component and aft passages including an axially downstream directional component in addition to a circumferential component; and the plurality of inlets are connected to corresponding ones of the first plurality of outlets by the forward passages and to corresponding ones of the second plurality of outlets by the aft passages. a plurality of inlets located on the first side of the wall portion at a first axial position, the plurality of inlets having a constant axial position relative to an axis of the engine; and a plurality of outlets located on a second side of the wall portion, wherein the plurality of outlets include a first plurality of outlets located axially upstream from a second plurality of outlets, characterised in that: the plurality of passages comprises alternating forward passages including an axially upstream directional component in addition to a circumferential component and aft passages including an axially downstream directional component in addition to a circumferential component; and the plurality of inlets are connected to corresponding ones of the first plurality of outlets by the forward passages and to corresponding ones of the second plurality of outlets by the aft passages. the plurality of passages comprises alternating forward passages including an axially upstream directional component in addition to a circumferential component and aft passages including an axially downstream directional component in addition to a circumferential component; and the plurality of inlets are connected to corresponding ones of the first plurality of outlets by the forward passages and to corresponding ones of the second plurality of outlets by the aft passages.