There are several methods for inspecting laser-drilled and electrical discharge machined cooling holes on aircraft engine turbine blades, vanes, nozzles, heat shields, and other similar parts. These holes are essential features of the cooling systems that protect critical components against the high temperatures that would otherwise damage them and even cause them to fail.

The only way to ensure the formation of a proper boundary layer of cooler air to protect these parts from the high engine temperatures is to verify that all of the cooling holes are present and at their proper location. This has always been a challenge and there has never been a good way to check these holes.

Probably the most common approach has been to carry out a simple visual check. Everyone agrees that this is very inaccurate and prone to human error.

Another scheme involves using a coordinate measuring machine (CMM) to check pins inserted in a few holes on a small sampling of parts mounted on sine plates to obtain the proper rotation and tilt angles. This is slow, labor intensive, and falls far short of the objective of inspecting 100 percent of the holes on 100 percent of the parts.

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