Sixth Flight, Antihistamine and a Rising Wind
You are flying a C1 drone for a friend's farm survey. It is the sixth flight of the day; you have had four hours' sleep and took a sedating antihistamine at 07:00 for hay fever. It is now 17:30. The wind has risen from 3 m/s to 7 m/s gusting 10 m/s, and the drone is 400 m away at 80 m AGL. The screen shows 28% battery and a return-to-home estimate of 4 minutes. Your friend says the last field is the important one and offers to ‘spot’ while you push on. You feel a headache and slight irritability.
1. Identify the human performance factors affecting your decision and explain how each could degrade safety.
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The factors compound: fatigue from four hours' sleep and a sixth flight slows reaction time and worsens risk assessment; sedating antihistamine can cause drowsiness and impaired attention even if you feel ‘used to it’; headache and irritability suggest dehydration, stress and waning concentration; social pressure from your friend creates plan-continuation bias; and the ‘spotter’ offer creates a false sense that extra eyes solve the problem.
Each degrades a different barrier: fatigue and medication reduce monitoring and decision quality; irritability can make you dismiss warning signs; social pressure pushes you to discount the 28% battery and rising wind. The spotter cannot extend your visual line of sight, cannot take control, and does not make you fit to fly. The combination is more dangerous than any single factor.
2. What should you do now, and what would you do differently before the day began?
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Now: stop the task and recover the aircraft while the battery and link are still usable. Fly a direct, controlled return or use RTH only if you are confident it will not fight the wind or climb into a worse position; monitor it and be ready to take over. Land, then do not launch again. Tell your friend the flight is over because you are not fit to continue.
Before the day: check medication warnings and do not fly after a sedating antihistamine; plan fewer flights with breaks; start only when rested; set personal wind and battery limits before leaving; use a checklist that includes fitness, medication, hydration and fatigue; and rehearse how to refuse ‘one more flight’ pressure. The legal and safety point is that fitness to fly is a continuous judgement, not a one-off signature.
3. If you decide to continue for one more 6-minute flight, what specific evidence would show that decision is unsafe?
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The evidence is the arithmetic and the human state together. At 28% battery, a 4-minute RTH estimate leaves very little margin; a 6-minute flight would consume more than the estimate, and the estimate may not account for a 7–10 m/s headwind or the cold/load effects on voltage. You would be landing with a reserve well below a sensible 20–30%, or not at all.
Add the human evidence: four hours' sleep, a sedating antihistamine, headache and irritability all point to degraded monitoring. If you find yourself rationalising with ‘the spotter will help’ or ‘the last field is important’, that is plan-continuation bias, not operational justification. The unsafe decision is identifiable because it relies on optimistic assumptions about wind, battery and your own performance.