Sonic IR has shown potential as a viable nondestructive inspection technique for crack detection by demonstrating that clearly identifiable signals can be generated where known cracks exist in certain structures1,2. However, before a technique can be used in a field environment, the factors that affect the reproducibility of the technique must be evaluated and their effect on the results of the technique understood. This will enable the control of these factors in the execution of an inspection procedure at, for example, an Air Force Depot Maintenance facility. In this program, sponsored by the Air Force Research Laboratory, we are taking a Design of Experiments (DoE) approach to determine the effect of several key variables on the results obtained from Sonic IR testing. A set of small samples with known fatigue cracks was tested according to a statistically designed test matrix. The design of this test matrix, the experimental setup, the test results, and conclusions will be presented.