A method for machining an airfoil section of a turbine blade or vane produced by a casting process, the airfoil section comprising an outer wall delimiting an airfoil interior having one or more internal cooling passages, the method comprising: receiving design data pertaining to the airfoil section, including a nominal outer airfoil form (40 N) and nominal wall thickness (T N) data; generating a machining path by determining a target outer airfoil form (40 T), the target outer airfoil form (40 T) being generated by adapting the nominal outer airfoil form (40 N) such that a nominal wall thickness (T N) is maintained at all points on the outer wall around the one or more internal cooling passages in a subsequently machined airfoil section, characterised in that determining the target outer airfoil form (40 T) comprises: measuring a three-dimensional outer form (40 A) of a cast airfoil section subsequently to the casting process, obtaining cooling passage position and form measurements for the internal cooling passages in relation to the measured outer form (40 A) of the cast airfoil section, constructing points around measured positions of the internal cooling passages which represent the nominal wall thickness (T N), performing an iterative best fit operation to align the nominal outer airfoil form (40 N) to the points representing nominal wall thickness (T N) values; and machining an outer surface of the airfoil section produced by the casting process according to said machining path, to remove excess material to conform to the generated target outer airfoil form (40 T), wherein obtaining the cooling passage position and form measurements for the one or more internal cooling passages in relation to the measured outer form (40 A) of the cast airfoil section, the cooling passage position and form measurements being carried out by obtaining actual wall thickness (T A) measurements at a plurality of points along the outer wall of the cast airfoil section; and wherein determining the target outer airfoil form (40 T) further comprises generating the target outer airfoil form (40 T) by adapting the nominal outer airfoil form (40 N) subsequent to the best fit alignment, so as to conform to points representing nominal wall thickness values that still deviate from the best fit alignment of the nominal outer airfoil form (40 N). receiving design data pertaining to the airfoil section, including a nominal outer airfoil form (40 N) and nominal wall thickness (T N) data; generating a machining path by determining a target outer airfoil form (40 T), the target outer airfoil form (40 T) being generated by adapting the nominal outer airfoil form (40 N) such that a nominal wall thickness (T N) is maintained at all points on the outer wall around the one or more internal cooling passages in a subsequently machined airfoil section, characterised in that determining the target outer airfoil form (40 T) comprises: measuring a three-dimensional outer form (40 A) of a cast airfoil section subsequently to the casting process, obtaining cooling passage position and form measurements for the internal cooling passages in relation to the measured outer form (40 A) of the cast airfoil section, constructing points around measured positions of the internal cooling passages which represent the nominal wall thickness (T N), performing an iterative best fit operation to align the nominal outer airfoil form (40 N) to the points representing nominal wall thickness (T N) values; and measuring a three-dimensional outer form (40 A) of a cast airfoil section subsequently to the casting process, obtaining cooling passage position and form measurements for the internal cooling passages in relation to the measured outer form (40 A) of the cast airfoil section, constructing points around measured positions of the internal cooling passages which represent the nominal wall thickness (T N), performing an iterative best fit operation to align the nominal outer airfoil form (40 N) to the points representing nominal wall thickness (T N) values; and machining an outer surface of the airfoil section produced by the casting process according to said machining path, to remove excess material to conform to the generated target outer airfoil form (40 T), wherein obtaining the cooling passage position and form measurements for the one or more internal cooling passages in relation to the measured outer form (40 A) of the cast airfoil section, the cooling passage position and form measurements being carried out by obtaining actual wall thickness (T A) measurements at a plurality of points along the outer wall of the cast airfoil section; and wherein determining the target outer airfoil form (40 T) further comprises generating the target outer airfoil form (40 T) by adapting the nominal outer airfoil form (40 N) subsequent to the best fit alignment, so as to conform to points representing nominal wall thickness values that still deviate from the best fit alignment of the nominal outer airfoil form (40 N).