A method for forming an airfoil (201; 202; 300; 500; 600; 780) for a gas turbine engine, the method comprising: forming an airfoil body (302; 502; 992) about a core assembly configured to define one or more internal cavities (530, 532, 534, 536; 632, 634; 783) of the airfoil body, the core assembly comprising at least one core structure (452, 454, 456, 458; 781; 990) having a purge slot protrusion (462; 782; 994) extending from a portion of the at least one core structure; removing the core assembly from the airfoil body to form one or more internal cavities (530, 532, 534, 536; 632, 634; 783), wherein at least one internal cavity has a cavity extension (642; 784) defined by the purge slot protrusion (462; 782; 994); and forming a squealer pocket (320; 620; 786) in a tip (310; 610; 785) of the formed airfoil body, wherein a cavity purge slot (326; 526; 628; 790) is formed at the cavity extension to fluidly connect the respective internal cavity with the squealer pocket, wherein the purge slot protrusion is a radially extending protrusion from a top of the at least one core structure, a radial height of the radially extending protrusion is equal to or less than five times a width of the radially extending protrusion, wherein the width is a thickness of the radially extending protrusion in a direction between a pressure side and a suction side of the formed airfoil body (302; 502; 992), wherein the squealer pocket (320; 620; 786) is formed by an electrode discharge machining process which removes material from the tip of the formed airfoil body; and wherein during the formation of the squealer pocket (320; 620; 786) in the tip (310; 610: 785) of the formed airfoil body, the electrode discharge machining process removes material from the tip to expose the cavity extension (642; 784) such that a connection with the cavity extension is formed to form the cavity purge slot (326; 526; 628; 790). forming an airfoil body (302; 502; 992) about a core assembly configured to define one or more internal cavities (530, 532, 534, 536; 632, 634; 783) of the airfoil body, the core assembly comprising at least one core structure (452, 454, 456, 458; 781; 990) having a purge slot protrusion (462; 782; 994) extending from a portion of the at least one core structure; removing the core assembly from the airfoil body to form one or more internal cavities (530, 532, 534, 536; 632, 634; 783), wherein at least one internal cavity has a cavity extension (642; 784) defined by the purge slot protrusion (462; 782; 994); and forming a squealer pocket (320; 620; 786) in a tip (310; 610; 785) of the formed airfoil body, wherein a cavity purge slot (326; 526; 628; 790) is formed at the cavity extension to fluidly connect the respective internal cavity with the squealer pocket, wherein the purge slot protrusion is a radially extending protrusion from a top of the at least one core structure, a radial height of the radially extending protrusion is equal to or less than five times a width of the radially extending protrusion, wherein the width is a thickness of the radially extending protrusion in a direction between a pressure side and a suction side of the formed airfoil body (302; 502; 992), wherein the squealer pocket (320; 620; 786) is formed by an electrode discharge machining process which removes material from the tip of the formed airfoil body; and wherein during the formation of the squealer pocket (320; 620; 786) in the tip (310; 610: 785) of the formed airfoil body, the electrode discharge machining process removes material from the tip to expose the cavity extension (642; 784) such that a connection with the cavity extension is formed to form the cavity purge slot (326; 526; 628; 790).