As the use of non-metallic composites continues to evolve in aerospace applications, it is important that ultrasonic (UT) inspectors become aware of the existence of resin rich conditions and their associated UT indications. UT techniques that rely on monitoring a backwall signal will generally miss these resin rich areas. The very common practice of through-transmission UT using non-contact squirter systems will usually miss resin rich indications. It is not unusual for a resin rich area to produce an intermediate indication that exceeds 100% Full Screen Height (FSH) and still have no significant effect on its corresponding backwall signal. This paper discusses the nature of resin rich indications, why they are missed, and why they are important to detect.

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