The paper reports the experimental stubby of detecting second-layer saw-cut in Boeing 747mid-spar lower chord by three modes: using combination of low frequency eddy current (LFEC) ring probe and SSEC III instrument and placing the probe on top of air gap, using combination of general remote fielded by current (GRFEC) ring probe and SSEC III and placing the probe on top of air gap, and using combination of GRFEC ring probe and SSEC III and placing the probe on top of fasteners. It turns out that all the three modes are capable of detecting the saw-cut. SNR analysis shows us that the last testing mode ensures high-enough SNR and can detect flaws smaller than those built in the standards. This may provide higher safety level in airworthiness.
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