Wind
Wind is the bulk movement of air across the Earth’s surface, caused by differences in atmospheric pressure.
Wind Patterns
When there is a difference in atmospheric pressure, air moves from the higher to the lower pressure area, resulting in winds of various speeds. In the Northern Hemisphere, this flow of air is deflected to the right, producing a clockwise circulation around high-pressure areas, known as anti-cyclonic circulation. Conversely, in low-pressure areas, air flows toward the low and is deflected to create a counter-clockwise or cyclonic circulation.
High-pressure systems are generally areas of dry, stable, descending air, often associated with good aviation weather. Conversely, air flows into a low-pressure area to replace rising air, which tends to be unstable and usually brings increasing cloudiness and precipitation, leading to bad aviation weather.
Wind Shears
Wind shear is a sudden, drastic change in wind speed and/or direction over a very small area. It can subject an aircraft to violent updrafts and downdrafts, as well as abrupt changes in horizontal movement. While wind shear can occur at any altitude, low-level wind shears are especially hazardous due to the proximity to the ground. Directional wind changes of 180° and speed changes of 50 knots or more are associated with low-level wind shear, commonly caused by passing frontal systems and thunderstorms. Pilots must be prepared to react immediately to maintain control of the aircraft.
Directional Winds
During flight, headwinds, crosswinds, and tailwinds affect the aircraft in various ways. Careful planning is essential before takeoff or landing.
Headwind
A headwind opposes the direction of the aircraft. Taking off into the wind allows the aircraft to use less runway, as the headwind generates part of the required lift, resulting in a lower ground speed and shorter takeoff distance. Climbing into the wind results in a steeper climb, ideal for an efficient climb out or avoiding obstacles. Landing into the wind has similar advantages, using less runway and achieving a lower ground speed at touchdown.
Crosswinds
A crosswind blows across the runway, making landings and takeoffs more challenging. It is important to know your aircraft’s crosswind limitations and avoid operating in conditions that exceed them.
Tailwind
A tailwind travels in the same direction as the aircraft, increasing ground speed and reducing the time required to reach the destination. However, taking off with a tailwind requires more runway and higher ground speeds to generate enough lift. As little as 5 knots of tailwind can increase rollout distance by 25%. Landing with a tailwind also poses challenges, as it increases ground speed during approach, which can visually confuse pilots and potentially lead to a stall if airspeed is lowered too much. It is best to avoid tailwinds during landing unless there is sufficient runway and the pilot has adequate experience.
Effects of Wind on Obstructions
When launching and recovering your aircraft, not every airfield or area will be free of obstructions. Whether it’s varying tree density on the outskirts of a woods or a cluster of man-made shelters, obstructions on the ground affect the flow of wind and can pose unseen dangers. It is important to be vigilant when flying in or out of areas with large buildings or natural obstructions near the runway. Walking your operational area and becoming familiar with varying wind patterns can help you better anticipate areas of sporadic wind gusts.
