Night Currency, Visual Line of Sight and a Crowded Riverbank
You are hired to film a fireworks display over a river at 22:30 local time with a 4.2 kg quadcopter. The launch site is a public park on the near bank; the far bank is 380 m away and hosts a road with moving traffic. Your observer stands beside you. Wind at the surface is calm, but the forecast shows a 12 kt gradient wind at 60 m. The client wants the aircraft hovering at 45 m over the water, 250 m from your position, for the 18-minute display. You hold a valid remote pilot certificate with night privileges, the aircraft is registered, and you have a signed landowner permission for the park. Your observer has normal vision but wears prescription glasses. You plan to fly with the anti-collision light on and the navigation lights on.
1. Identify the regulatory and operational problems in this plan and state what you must change before launch.
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Two separate issues must be resolved before launch: one legal, one practical.
Legal/visibility. Operations must keep the aircraft within visual line of sight of the remote pilot or a trained observer in continuous communication with the pilot. At 250 m over water at night, with a 4.2 kg airframe and a 45 m hover, the aircraft subtends a very small angle; the observer's glasses are acceptable only if corrected vision meets the required standard, and this must be confirmed, not assumed. The observer must be able to see the aircraft and the surrounding airspace, not just the lights. If the observer cannot reliably acquire and hold the aircraft, the sortie is not compliant regardless of the lights fitted. Reduce distance, reposition the observer, or both.
People and property below. The far bank road with traffic is a populated area and moving vehicles are not participating in the operation. A 45 m hover over water does not by itself guarantee that a loss of control or a fly-away cannot reach the road; you must plan a forced-landing/emergency area and a flight path that keeps a safe distance from the road and from uninvolved people. Hovering over water also removes any benign landing option.
Changes before launch. Move the observer to a position that shortens the slant range (for example, a point on the near bank closer to the display axis), confirm corrected vision, brief lost-sight procedure (hold position or climb, do not translate), set a hard minimum-fuel/battery reserve for return, and define an abort criterion if the aircraft cannot be reacquired within a few seconds. Confirm the night lighting configuration is the one required for your aircraft and that it does not blind the observer.
2. The wind at 60 m is 12 kt from the direction that pushes the aircraft toward the far bank. Explain how you would manage this during an 18-minute hover and what reserve you would keep.
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A 12 kt wind at 60 m is roughly 6 m/s. A hovering multirotor must tilt into wind to hold position, so it consumes more power than in still air, and the effect grows with wind speed and with any gust factor. The aircraft is downwind of you relative to its commanded position, meaning that if it loses link or a motor, drift carries it toward the road on the far bank - the worst direction.
Management:
- Fly the hover at the lowest height that still gives a clean shot, because wind speed falls with height near the surface; 45 m may be unnecessarily high.
- Position the aircraft so that the wind pushes it away from the road, not toward it, or reduce the stand-off distance so a drift-back has room.
- Set a conservative reserve: plan to land with at least 20-25% remaining, and treat the display as a series of short segments with a return-to-home check between them rather than one continuous 18-minute hover.
- Brief the abort: if wind at height exceeds the aircraft's demonstrated hover capability with margin, or if the aircraft is being pushed toward the far bank, terminate the hover and recover.
Do not rely on the surface calm; the 60 m wind is what the aircraft experiences, and the gradient means the hover altitude matters.