Defects in optical fibers are detected during manufacturing by using three bandpass filters to separate signals from a scattered light signal produced by a light source in a fiber measurement system. The separated signals include a clad diameter signal, a regular airline signal and a core airline signal. The regular airline signal is compared with the clad diameter signal to produce a normalized regular airline signal, and the core airline signal is compared with the clad diameter signal to produce a normalized core airline signal. The normalized regular airline signal and normalized core airline signal are monitored to determine if they increase, which indicates the presence of a defect in the optical fiber.