Subjective Fatigue Across Multiple Sectors in Super Short-haul High-Frequency Operations: An Observational Study of Japanese Regional Airline Pilots

Objective: To examine the effect of sector count on subjective fatigue in super short-haul high-frequency (SSH-HF) operations (≥five sectors, block-time <1 h) among Japanese regional airline pilots. Methods: We surveyed 147 line pilots at three Japanese regional carriers, assessing severe fatigue (Samn-Perelli Scale ≥6) after the second, fourth, and sixth sectors of six-sector duties. Multivariable mixed-effects models, stratified by workload tertile, were used. Results: Adjusted predicted probability of severe fatigue increased from 1.8% at sectors 1–2 to 37.0% at sectors 5–6. Heavy workload was associated with greater fatigue in the final sector pair, with a clear divergence from the low- and moderate-workload groups. Conclusions: Fatigue accumulates progressively with sector count in SSH-HF operations, particularly under high workload. These findings provide rationale for flexible fatigue risk management incorporating workload considerations within prescriptive regulatory limits.