Crosswind Limit, Contaminated Runway and the Go-Around Decision
You are approaching a 1,800 m runway in a light twin. Reported wind is 310°/18 kt gusting 26 kt; the runway is 27 (270° magnetic). Light rain has left the runway damp with patches of standing water near the touchdown zone, and braking action is reported as medium. Your aircraft's crosswind limit is 20 kt (maximum demonstrated), and the manual gives a wet-runway landing distance of 1,050 m at maximum landing mass, no wind, sea level. Field elevation is 30 ft, temperature 24 °C, QNH 1008. You are 80 kg below maximum landing mass and have 1,900 m of runway available including the displaced threshold. On short final you experience a 15 kt gain in headwind, then a loss of 20 kt at 200 ft.
1. Compute the crosswind and gust components and assess them against the aircraft limit.
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Wind is 310°, runway 270°, so the angle between wind and runway is 40°.
Crosswind = wind speed × sin(40°) = 18 × 0.643 = 11.6 kt for the steady wind. For the gust: 26 × 0.643 = 16.7 kt.
Headwind component = wind speed × cos(40°): 18 × 0.766 = 13.8 kt steady, 26 × 0.766 = 19.9 kt in the gust.
The steady crosswind of about 12 kt and the gust crosswind of about 17 kt are both within the 20 kt limit, but the gust value is only about 3 kt below it. Two cautions apply. First, the limit is a maximum demonstrated value, not a guarantee, and it is determined in steady conditions; gust spread of 8 kt means the actual crosswind varies between roughly 12 and 17 kt continuously. Second, the crosswind limit is a handling limit and says nothing about the runway surface; on a damp runway with standing water, directional control and braking are both degraded. A sensible personal limit would be well below 17 kt gusting in these conditions.
2. Assess the landing distance against the available runway and the effect of the windshear report.
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Start from the wet-runway figure of 1,050 m at maximum landing mass, sea level, no wind. Field elevation 30 ft and 24 °C are close to ISA (ISA at 30 ft is about 15 °C, so deviation is about +9 °C), which adds a small factor, perhaps 5%, giving about 1,100 m. Being 80 kg below maximum landing mass reduces the distance slightly, perhaps 2–3%, so around 1,070 m.
The headwind component of about 14 kt steady reduces ground distance, but the gust to 20 kt and the shear mean you cannot rely on it; conservative practice is to plan with the steady wind only or with no wind at all. On that basis 1,070 m against 1,900 m available looks comfortable - a margin of over 800 m, or about 43%.
However, the reported braking action of medium and the standing water change the picture. The manual's wet figure may not represent standing water, where dynamic aquaplaning becomes possible above roughly 8–9 kt ground speed for typical tyre pressures, and braking can effectively disappear. The margin is large enough that the runway length itself is not the limiting factor; the limiting factors are directional control and stopping performance on the contaminated surface.
3. On short final you gain 15 kt then lose 20 kt at 200 ft. Decide and justify the action.
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The sequence is a classic windshear encounter: an increasing headwind raises IAS and tempts the pilot to reduce power and lower the nose, then the loss of 20 kt at 200 ft causes a rapid loss of IAS and lift close to the ground. The correct action is to go around immediately and fully: apply maximum take-off power, establish the pitch attitude for the go-around, and do not attempt to salvage the approach. At 200 ft there is insufficient height to recover from a stall or a hard contact if the shear continues.
Justification: the aircraft is 20 kt below the target approach speed in a gusty, sheared airflow over a contaminated runway. Even if the aircraft could be re-stabilised, the touchdown would be long and directional control on standing water uncertain. The go-around is the option that preserves margin, and the aircraft has the performance to do it.
After the go-around, do not simply re-attempt the same approach. Consider holding for improvement, using a more favourable runway if one exists, diverting to an airport with better conditions, or landing only when the wind and surface reports give a comfortable margin. If a second approach is made, use a higher approach speed increment for the gust and plan to touch down early with firm braking rather than floating.