Crew Fatigue and Handover on a Night Perimeter Patrol
A two-person crew is conducting a night perimeter patrol of an industrial site with a 5.5 kg multirotor. The remote pilot has been on duty since 06:00 and it is now 23:30. The visual observer joined at 18:00 after a full day of other work. The patrol requires continuous coverage, and the crew has flown four 40-minute sorties with 15-minute battery swaps. The site is lit by sodium lamps, and the aircraft's anti-collision light is the only other illumination. The remote pilot reports difficulty reading the telemetry tablet and has twice misread the altitude. The observer has become quiet and has stopped calling out the aircraft's position. The next crew is not available until 06:00.
1. Assess the human factors and state whether the crew should continue.
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The remote pilot has been on duty for 17.5 hours, which is well beyond the point at which fatigue degrades vigilance, reaction time and error detection. The observer has been on duty for 5.5 hours after a full day of other work, which means the observer's total waking period is likely 17 hours or more. Both are fatigued.
The symptoms are specific and serious. Difficulty reading the tablet at night suggests either fatigue-related visual strain or a display brightness and contrast problem, and misreading the altitude twice is a direct indication that the pilot's instrument scan is failing. The observer's silence is a classic sign of withdrawal and reduced vigilance; a visual observer who stops calling out position is no longer providing the monitoring function that justifies the two-person crew.
I would stop the operation. The patrol is continuous, but continuous coverage is an operational desire, not a safety requirement that overrides fitness for duty. I would land the aircraft at the earliest safe opportunity, inform the site operator that coverage is suspended, and hand over to the next crew at 06:00. If coverage is genuinely critical, the site operator must provide a relief crew or accept the gap.
2. What could have been done differently in planning and in the cockpit to prevent this state?
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Planning: the duty period should have been limited to a defined maximum, with a rest break before the night sorties. A crew that starts at 06:00 should not be flying at 23:30. The schedule should have been built around the night patrol, with the crew resting during the day, or a third person should have been available for relief. The 15-minute battery swaps are not rest; they are work.
Cockpit: the display brightness should have been set for night conditions, with a dimmed tablet and a red-light-friendly interface, and the pilot should have used a hood or shield to reduce glare from the sodium lamps. The altitude should be called out by the observer as a cross-check, not read silently by the pilot. A sterile-cockpit rule during critical phases and a standard callout sequence would have made the observer's silence obvious earlier.
I would also have used a fatigue checklist at the start of each sortie: hours awake, hours on duty, last rest, and a self-assessment. Two misreads of altitude are a stop signal, not a warning.
3. Design a handover briefing for the 06:00 crew that captures the safety-critical information.
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The handover should be structured and written, not verbal only. It should cover the aircraft status: airframe hours, battery cycles and state of charge, any anomalies, and the maintenance log. It should cover the operation: the patrol route, the current coverage gap, the site hazards, the lighting conditions and the radio frequencies.
It should cover the human factors: the previous crew's duty hours and fatigue state, the errors observed, and the decision to suspend operations. It should cover the environment: the weather forecast for the next 12 hours, the wind at altitude, and any changes to the site's activities.
It should cover the handover of responsibility: who is the remote pilot in command for the next period, who is the observer, and what the abort criteria are. Both crews should sign the handover, and the incoming crew should have the opportunity to ask questions and to decline the sortie if they are not fit. The outgoing crew should not leave until the incoming crew has confirmed understanding.