Airport weather can change over very short distances, especially near runways, terminals, hangars, hills, and open snowfields. A pilot may see acceptable conditions a few kilometers away but encounter dangerous gusts, wind shear, or blowing snow on final approach. These local hazards matter because aircraft are slow, low, and close to the ground during takeoff and landing.
Small changes in wind or visibility can quickly reduce lift, control, and runway awareness.
Key Facts
- Headwind component = wind speed x cos(angle between wind and runway).
- Crosswind component = wind speed x sin(angle between wind and runway).
- Wind shear is a rapid change in wind speed or direction over a short distance.
- Lift depends strongly on airspeed: L = 1/2 rho v^2 S CL.
- A sudden tailwind or loss of headwind lowers airspeed over the wings and can reduce lift.
- Blowing snow can lower runway visual range even when the main cloud ceiling is high.
Vocabulary
- Wind shear
- Wind shear is a sharp change in wind speed or direction over a short horizontal or vertical distance.
- Gust
- A gust is a brief increase in wind speed that can suddenly change an aircraft's airspeed and attitude.
- Crosswind
- A crosswind is the component of wind that blows across the runway rather than along it.
- Runway visual range
- Runway visual range is the distance a pilot can see along the runway using lights, markings, and instruments.
- Blowing snow
- Blowing snow is snow lifted from the ground by wind, which can reduce visibility near the surface even without new snowfall.
Common Mistakes to Avoid
- Treating the airport weather report as uniform across the whole airport is wrong because buildings, terrain, and open fields can create local wind and visibility changes.
- Ignoring wind direction relative to the runway is wrong because the same wind speed can produce very different headwind and crosswind components.
- Assuming high visibility above the runway means safe landing visibility is wrong because blowing snow can create a shallow near-ground whiteout layer.
- Using average wind speed instead of gust speed is wrong because aircraft control limits and landing decisions often depend on the strongest expected gusts.
Practice Questions
- 1 A wind of 20 m/s blows 30 degrees from the runway heading. Calculate the headwind component and crosswind component.
- 2 An aircraft approaches at 62 m/s airspeed with a 12 m/s headwind. If the headwind suddenly drops to 4 m/s while ground speed stays nearly constant for a moment, what is the new airspeed relative to the air?
- 3 Explain why a terminal building or row of hangars can create a dangerous zone for an aircraft landing in strong winter winds, even if the airport weather station reports acceptable conditions.