Southwest Flight 1380 – Slipping through the Cracks

Fan blades in flight engines are subject to cyclic stresses (e.g., during startup and shutdown) that could lead to fatigue damage and eventual fracture. Accordingly, fan blades are subject to regular nondestructive inspections to detect cracks to prevent fan blade liberations (known as “fan blade out” events) from occurring. Further, flight engines are designed and certified to contain fan blade outs to prevent engine failure and damage to nearby structural components (such as the fan cowl). Even if a crack is not detected and a fan blade out events occurs, it should not result in pieces of the cowl dislodging.

In the case of Southwest Airlines Flight 1380, a fan blade out resulted in pieces of the cowl dislodging and impacting the fuselage, resulting in cabin depressurization and one passenger fatality (and other passenger injuries). While the blade liberation was determined to be due to a low-cycle fatigue crack that initiated at the blade dovetail, the NTSB found that this fatigue crack went undetected during its many regular inspections. Ultimately, these inspection protocols were modified to include enhanced nondestructive evaluation methods to improve crack detectability, and the NTSB further recommended that fan blade out certification testing should consider critical fan blade impact locations that could result in pieces of cowl dislodging.

This presentation discusses the fan blade out event that precipitated the Southwest Flight 1380 accident: the factors that led to the initiation of the fatigue crack, how it was not detected during the inspections, and the corrective actions taken to the nondestructive evaluation protocol to mitigate fan blade outs from recurring.