A turbine airfoil , comprising: a body having an airfoil wall; said body further comprising a base and tip disposed opposite the base, and a pressure sidewall and suction sidewall extending between a leading edge and a trailing edge ; a coolant chamber within the body ; and a plurality of cooling passages within the airfoil wall, each cooling passage including: a first portion extending from a first point on an exterior surface of the airfoil wall to the coolant chamber , a second portion extending from a second point on the exterior surface of the airfoil wall distal from the first point to intersect a mid-portion of the first portion , and a cap element closing the first portion at the first point but leaving the second portion open, wherein each cooling passage has a single inlet in fluid communication with the coolant chamber and a single outlet at the second point of the second portion ; and characterised in that the cap element includes a metal plug in the first portion at or near the first point , and further comprising a thermal barrier coating (TBC) covering the exterior surface of the airfoil wall, the second portion of each cooling passage extending through the TBC at the second point thereof. a body having an airfoil wall; said body further comprising a base and tip disposed opposite the base, and a pressure sidewall and suction sidewall extending between a leading edge and a trailing edge ; a coolant chamber within the body ; and a plurality of cooling passages within the airfoil wall, each cooling passage including: a first portion extending from a first point on an exterior surface of the airfoil wall to the coolant chamber , a second portion extending from a second point on the exterior surface of the airfoil wall distal from the first point to intersect a mid-portion of the first portion , and a cap element closing the first portion at the first point but leaving the second portion open, wherein each cooling passage has a single inlet in fluid communication with the coolant chamber and a single outlet at the second point of the second portion ; and characterised in that the cap element includes a metal plug in the first portion at or near the first point , and further comprising a thermal barrier coating (TBC) covering the exterior surface of the airfoil wall, the second portion of each cooling passage extending through the TBC at the second point thereof. a first portion extending from a first point on an exterior surface of the airfoil wall to the coolant chamber , a second portion extending from a second point on the exterior surface of the airfoil wall distal from the first point to intersect a mid-portion of the first portion , and a cap element closing the first portion at the first point but leaving the second portion open, wherein each cooling passage has a single inlet in fluid communication with the coolant chamber and a single outlet at the second point of the second portion ; and characterised in that the cap element includes a metal plug in the first portion at or near the first point , and further comprising a thermal barrier coating (TBC) covering the exterior surface of the airfoil wall, the second portion of each cooling passage extending through the TBC at the second point thereof. <EOS>