A combustor for a gas turbine engine having a longitudinal centerline, the combustor comprising: an annular shell (52; 54); an annular bulkhead connected to the shell (52; 54); a heat shield panel having a first surface facing a combustion chamber and a second surface opposite the first surface, the heat shield panel mounted to the bulkhead and defining a cooling chamber between the bulkhead and the heat shield panel, the heat shield panel having a wall extending from the heat shield panel toward the bulkhead around at least a portion of a periphery of the heat shield panel, the wall including a circumferential wall portion (128; 130) including at least one cooling air passage (136; 140) extending between the cooling chamber and a cavity (132; 134) defined between the circumferential wall portion (128; 130) and the shell (52; 54); and a liner panel mounted to the shell (52; 54), the liner panel having a first end portion at a first end of the liner panel, the first end portion further defining the cavity (132; 134), wherein the at least one cooling air passage (136; 140) is configured to purge the cavity (132; 134) by directing a first cooling air stream (138; 142) from the cooling chamber into the cavity (132; 134), wherein the liner panel has a first surface facing away from the shell (52; 54) and a second surface opposite the first surface of the liner panel, the liner panel comprising a liner wall extending from the second surface of the liner panel at the first end of the liner panel and contacting the shell (52; 54), characterised in that the first end portion of the liner panel is configured to direct the first cooling air stream (138; 142) from the cavity (132; 134) to the first surface of the heat shield panel. an annular shell (52; 54); an annular bulkhead connected to the shell (52; 54); a heat shield panel having a first surface facing a combustion chamber and a second surface opposite the first surface, the heat shield panel mounted to the bulkhead and defining a cooling chamber between the bulkhead and the heat shield panel, the heat shield panel having a wall extending from the heat shield panel toward the bulkhead around at least a portion of a periphery of the heat shield panel, the wall including a circumferential wall portion (128; 130) including at least one cooling air passage (136; 140) extending between the cooling chamber and a cavity (132; 134) defined between the circumferential wall portion (128; 130) and the shell (52; 54); and a liner panel mounted to the shell (52; 54), the liner panel having a first end portion at a first end of the liner panel, the first end portion further defining the cavity (132; 134), wherein the at least one cooling air passage (136; 140) is configured to purge the cavity (132; 134) by directing a first cooling air stream (138; 142) from the cooling chamber into the cavity (132; 134), wherein the liner panel has a first surface facing away from the shell (52; 54) and a second surface opposite the first surface of the liner panel, the liner panel comprising a liner wall extending from the second surface of the liner panel at the first end of the liner panel and contacting the shell (52; 54), characterised in that the first end portion of the liner panel is configured to direct the first cooling air stream (138; 142) from the cavity (132; 134) to the first surface of the heat shield panel.