Background We compared fatigue and performance of 3-man aircrew (MC) to 4 MC for Southeast Asia to London long haul flights (>12 hours).

Methods Sleep diary and wearable actigraph data were collected before and during the flights and layover. Samn Perelli Crew Status Check Scores (SPS), Karolinska Sleepiness Scale (KSS) scores and objective Psychomotor Vigilance Test (PVT) scores were recorded during the flights.

Results Nineteen aircrew flying 19 4MC flights and 6 3MC flights were studied. Flight and duty hours in the last 2 and 12 months were similar for those on 4MC and 3MC flights. Those on 3MC flights slept about 2 hours more than 4MC flights in the 2 days before the outbound flight. On outbound and inbound flights, the 3MC slept about an hour less than the 4MC, but duration of layover sleep was similar. Aircrew KSS and SPS scores for outbound and inbound flights were similar for 4MC and 3MC flights, but some scores of 8 or more on KSS and 6 or more on SPS (which may be of concern) were reported. PVT readings (median reaction times, number of lapses, mean fastest 10% reaction times, mean slowest 10% reaction times) were comparable between 4MC and 3MC during outbound and inbound flights. While PVT readings deteriorated over the flight duration, none of the readings were at levels of concern for operations.

Conclusion Physiological performance and fatigue measurements suggest no absolute contraindication for deployment of 3MC long haul Southeast Asia to London flights.