Abstract: A gas turbine engine (10) and an airfoil (50) for use therein, the airfoil (50) having a structure (128) containing cooling passageways (110, 120) extending between a chamber (100) and a series of apertures (78) positioned along the trailing edge (72) through which cooling fluid (144) received from the chamber (100) exits the airfoil (50), wherein the structure (128) is characterized by a variable thickness (t) between the pressure and suction sidewalls (74, 76) of the airfoil as a function of position along the cooling passageways (110, 120) such that each in a plurality of cooling passageways are characterized by a cross sectional flow area (170, 174) which decreases as a function of distance from the chamber (100).