A gas turbine engine comprising: an engine case; an upstream vane; and a seal assembly, the seal assembly comprising: a blade outer air seal comprising a radially outer surface; a downstream vane coupled to and aft of the blade outer air seal via a first fluid sealing engagement; a blade outer air seal support disposed radially outward of the blade outer air seal and configured to be a pressure wall having a radially inner side and a radially outer side, the pressure wall being coupled on a downstream side to the blade outer air seal via a second fluid sealing engagement and disposed between the blade outer air seal and the engine case, the pressure wall being coupled on an upstream side to at least one of the engine case and the upstream vane via a third fluid sealing engagement (131, 132), the pressure wall dividing the volume that is radially outward of the blade outer air seal into a first plenum and a second plenum, the pressure wall defining a metering orifice, characterised in that: the upstream vane is coupled to and forward of the blade outer air seal; the metering orifice extends from the radially inner side to the radially outer side of the pressure wall and is configured to meter air flow directly from the first plenum upstream of the pressure wall to the second plenum downstream of the pressure wall; fluid communication between the first plenum and the second plenum is restricted to the metering orifice of the pressure wall; the first plenum is defined by a preponderant portion of the radially outer surface of the blade outer air seal, the radially inner side, and at least one of the engine case and the upstream vane; and the second plenum is defined by the first fluid sealing engagement, the radially outer side, and at least one of the engine case and the downstream vane. an engine case; an upstream vane; and a seal assembly, the seal assembly comprising: a blade outer air seal comprising a radially outer surface; a downstream vane coupled to and aft of the blade outer air seal via a first fluid sealing engagement; a blade outer air seal support disposed radially outward of the blade outer air seal and configured to be a pressure wall having a radially inner side and a radially outer side, the pressure wall being coupled on a downstream side to the blade outer air seal via a second fluid sealing engagement and disposed between the blade outer air seal and the engine case, the pressure wall being coupled on an upstream side to at least one of the engine case and the upstream vane via a third fluid sealing engagement (131, 132), the pressure wall dividing the volume that is radially outward of the blade outer air seal into a first plenum and a second plenum, the pressure wall defining a metering orifice, characterised in that: the upstream vane is coupled to and forward of the blade outer air seal; the metering orifice extends from the radially inner side to the radially outer side of the pressure wall and is configured to meter air flow directly from the first plenum upstream of the pressure wall to the second plenum downstream of the pressure wall; fluid communication between the first plenum and the second plenum is restricted to the metering orifice of the pressure wall; the first plenum is defined by a preponderant portion of the radially outer surface of the blade outer air seal, the radially inner side, and at least one of the engine case and the upstream vane; and the second plenum is defined by the first fluid sealing engagement, the radially outer side, and at least one of the engine case and the downstream vane. a blade outer air seal comprising a radially outer surface; a downstream vane coupled to and aft of the blade outer air seal via a first fluid sealing engagement; a blade outer air seal support disposed radially outward of the blade outer air seal and configured to be a pressure wall having a radially inner side and a radially outer side, the pressure wall being coupled on a downstream side to the blade outer air seal via a second fluid sealing engagement and disposed between the blade outer air seal and the engine case, the pressure wall being coupled on an upstream side to at least one of the engine case and the upstream vane via a third fluid sealing engagement (131, 132), the pressure wall dividing the volume that is radially outward of the blade outer air seal into a first plenum and a second plenum, the pressure wall defining a metering orifice, characterised in that: the upstream vane is coupled to and forward of the blade outer air seal; the metering orifice extends from the radially inner side to the radially outer side of the pressure wall and is configured to meter air flow directly from the first plenum upstream of the pressure wall to the second plenum downstream of the pressure wall; fluid communication between the first plenum and the second plenum is restricted to the metering orifice of the pressure wall; the first plenum is defined by a preponderant portion of the radially outer surface of the blade outer air seal, the radially inner side, and at least one of the engine case and the upstream vane; and the second plenum is defined by the first fluid sealing engagement, the radially outer side, and at least one of the engine case and the downstream vane.