Prepared for: Assistant Commandant of the Marine CorpsA midair collision in the early morning hours of December 6, 2018 resulted in the tragic deaths of six US Marine Corps aircrew
members and the loss of two aircraft, a KC-130 tanker and an F/A-18. The mishap occurred around 2 AM during a routine nighttime
air refueling training mission off the coast of Japan. In the investigation that followed, fatigue was identified as a major contributor;
the transition from day to night flights was called out as a problem area that continues to plague aviation commands. Subsequent
investigations confirmed findings and requested help from the Naval Postgraduate School (NPS) Crew Endurance Team to study the
problem and make recommendations for safer transition from day to night flight operations. The study goal was to provide
recommendations to the fleet regarding the limitations and best practices for shifting aviators from day to night operations. After
reviewing the scientific literature, NPS designed a study to determine the efficacy of high energy visible (HEV) light exposure in
shifting the circadian rhythms of study participants. The project was a hybrid study of military aviators who, as graduate students at
NPS, continued normal daily schedules but came into the laboratory for 6 to 8 hours on three consecutive evenings. The study
attempted to replicate the patterns of aviators who could potentially be required to abruptly shift to night flight operations.
Results showed that a single 4-hour exposure of blue-enriched white light (~1000 lux) successfully delayed the circadian phase of all
participants an average of 1 hour 19 minutes (range 53 minutes to 1 hour 56 minutes). Melatonin onset was delayed in all participants.
This circadian shift is estimated to be a 10-fold increase over what would be achieved without the HEV light. Light was shown to
have an alerting effect with participants reporting less sleepiness and reduced subjective workload with improved flight performance.
Conclusions from the literature review and our study indicate that circadian entrainment in military operational settings should use
light management as the dominant method for shifting the circadian clock. In general, it is expected that higher rates of adaptation
(i.e., more rapid entrainment) will occur by aligning and applying multiple synchronization methods simultaneously, i.e., light
management combined with strategically timed exercise, meals, melatonin, and caffeine. Based on these conclusions, we developed
general recommendations and two circadian synchronization plans for crewmembers switching from day to night operations. One plan
shows a schedule that prepares for night operations shifting over multiple days. The other shows a schedule for crewmembers required
to shift from abruptly without notice. These plans warrant further development in an operational environment to ensure they can be
implemented safely and effectively.Assistant Commandant of the Marine CorpsAssistant Commandant of the Marine CorpsApproved for public release; distribution is unlimite
