Convective Build-Up and a Marginal Crosswind
You plan a 25-minute inspection flight at 60 m AGL in an urban-fringe area. The morning forecast was for light winds, but by mid-afternoon the surface wind is 14 kt gusting 22 kt across the runway, and cumulus is building rapidly to the west with a dark base and visible virga. The temperature is 31 °C and the dewpoint is 19 °C. Your landing area is a small cleared lot with a fence line 15 m downwind of the touchdown point. The aircraft is a 5 kg multirotor with a published maximum wind resistance of 10 m/s. The client is pressing for the flight because the inspection is due today.
1. Evaluate the weather against the aircraft limits and the landing area.
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The wind is at or beyond the aircraft's margin. A 22 kt gust is about 11.3 m/s, above the published 10 m/s maximum wind resistance, and gusts are what matter for control authority and drift. The 15 m fence line downwind of touchdown leaves almost no room for a gust-induced overshoot.
The convective picture reinforces the caution: a temperature of 31 °C with a dewpoint of 19 °C gives a spread of 12 °C, and rapidly building cumulus with virga to the west signals developing convection, possible gust fronts, and outflow that can produce sudden wind shifts stronger than the surface reading. The forecast being wrong about the wind is itself a reason to distrust the rest of it.
2. The client insists. What is your decision, and how do you justify it?
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Do not fly. The justification is not the client's schedule; it is that the operation would exceed the aircraft's wind limit in gusts, the landing area has no downwind margin, and convective outflow could produce conditions worse than the measured wind with little warning.
The decision is defensible on three independent grounds:
- Aircraft limit: gusts above the published maximum wind resistance.
- Site limit: 15 m to a fence downwind is insufficient for a gust overshoot.
- Weather trend: building convection with virga means the wind is likely to become more variable, not less.
Offer alternatives: reschedule to the morning, relocate to a more open landing area with a longer into-wind approach, or reduce scope. 'Due today' is a commercial pressure, not an operational justification.
3. If you were to fly a reduced task, what conditions would you set and what would you monitor?
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Only if the wind drops to a sustained and gust value comfortably below the aircraft limit (e.g., gusts well under 10 m/s) and the convection remains distant and non-threatening:
- Use the open landing area with a long into-wind approach and a clear go-around path.
- Set a hard abort if gusts approach the limit or if virga or a gust front approaches.
- Monitor surface wind continuously, watch the western sky for outflow, and keep the flight short and close.
- Brief the observer to call any change in wind or sky immediately.
If any of these conditions cannot be met, the reduced task is not worth the risk; reschedule.