A method for forming an airfoil (300; 500; 600; 780) for a gas turbine engine, the method comprising: forming an airfoil body (302; 502) 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) having a purge slot protrusion (462; 782) extending from a portion of the core structure; removing the core assembly from the airfoil body to form one or more internal cavities, wherein at least one internal cavity has a cavity extension (542; 642; 784) defined by the purge slot protrusion; and forming a squealer pocket (320; 520; 620; 786) in a tip (310; 510; 610; 785) of the formed airfoil body, wherein a cavity purge slot (328; 528; 628; 790) is formed at the cavity extension to fluidly connect the respective internal cavity with the squealer pocket, characterized in that: the squealer pocket (320; 520; 620; 786) is formed by an electrode discharge machining process which removes material from the tip of the formed airfoil body; and in that during the formation of the squealer pocket (320; 520; 620; 786) in the tip (310; 510; 610; 785) of the formed airfoil body, the electrode discharge machining process cuts a recess that extends radially inward farther than a base of the squealer pocket to cut into the cavity extension to form the cavity purge slot (328; 528; 628; 790). forming an airfoil body (302; 502) 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) having a purge slot protrusion (462; 782) extending from a portion of the core structure; removing the core assembly from the airfoil body to form one or more internal cavities, wherein at least one internal cavity has a cavity extension (542; 642; 784) defined by the purge slot protrusion; and forming a squealer pocket (320; 520; 620; 786) in a tip (310; 510; 610; 785) of the formed airfoil body, wherein a cavity purge slot (328; 528; 628; 790) is formed at the cavity extension to fluidly connect the respective internal cavity with the squealer pocket, characterized in that: the squealer pocket (320; 520; 620; 786) is formed by an electrode discharge machining process which removes material from the tip of the formed airfoil body; and in that during the formation of the squealer pocket (320; 520; 620; 786) in the tip (310; 510; 610; 785) of the formed airfoil body, the electrode discharge machining process cuts a recess that extends radially inward farther than a base of the squealer pocket to cut into the cavity extension to form the cavity purge slot (328; 528; 628; 790). the squealer pocket (320; 520; 620; 786) is formed by an electrode discharge machining process which removes material from the tip of the formed airfoil body; and in that during the formation of the squealer pocket (320; 520; 620; 786) in the tip (310; 510; 610; 785) of the formed airfoil body, the electrode discharge machining process cuts a recess that extends radially inward farther than a base of the squealer pocket to cut into the cavity extension to form the cavity purge slot (328; 528; 628; 790).