(57) A method for forming an airfoil, a core for forming an airfoil, and an airfoil for a gas turbine engine are described. The method includes forming an airfoil body (302; 502; 992) about a core assembly (450), the core assembly comprising at least one core structure (452, 454, 456, 458; 781; 990) having a radially extending 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 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. The radially extending protrusion has a radial height that is equal to or less than five times a width thereof.
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