The Joint Strike Fighter jet engine contains more than 1.2 million holes. Many are film cooling holes vital for engine operation at the elevated temperatures that enable reduced fuel consumption. Engine maNUfacturers stress the need for repeatability in the diameter of these holes. The measure of repeatability is the standard deviation (σ).1 For a design diameter D0 = 500μm, laser percussion drilled holes currently have a diameter standard deviation of σ ≈ 20μm. Laser trepanning currently yields σ ≈ 15μm. For a Gaussian error distribution and 1.2 million holes, Table 1 shows the number of holes NI with D inside the interval (D0 – 1σ) to (D0 + 1σ), the number of holes NOoutside that interval, and the especially critical number of undersized holes NU outside that interval. Because the Gaussian distribution is symmetric, NU = ½ NO. The Hagen-Poiseuille equation2 for fluid flow through small holes shows flow rate proportional to D04. Figure 1 plots the NOrmalized film cooling flow rate, Φ vs. σ, for D0 = 500μm holes, an error interval D = D0- 5σ, and NU = 1. For this case, the NOrmalized flow function is defined by: From Figure 1, for σ = 20μm and NU = 1, Φ = 0.41 or only 41%...