For any pilot, safety is of the utmost importance. Several things can affect both the safety and quality of a flight, including weather and atmospheric conditions.
Aside from rain and fog, which can cause reduced flying visibility, weather conditions such as wind shear can have a significant impact on your flying experience. Wind shear is a change in wind speed or direction over a short distance. These rapidly changing wind currents are one cause of turbulence, and extremely strong windshears can create very challenging flying conditions for pilots.
At Gold Seal, our goal is to ensure you have the best possible flying experience. As a pilot, it’s critical to understand how different circumstances can affect your flight so you can be prepared for any possible situation. We want to prepare you to become a skilled aviator, so here is some important information you should know about wind shear before stepping into the cockpit.
What Is Wind Shear?
As previously mentioned, wind shears are rapidly changing wind currents that occur over a short distance. They can occur at either high or low altitudes and are divided into two categories: horizontal and vertical.
Horizontal wind shear occurs when an airplane passes through a wind shift plane. They are typically seen near the coast and across different weather fronts. Horizontal wind shear can change your course and airspeed and are most dangerous when an aircraft is flying at a low altitude. It is considered severe when horizontal velocity changes at least 15 meters a second over distances of one to four kilometers.
Vertical wind shear is the most common type of wind shear and is most dangerous near the ground. It can affect airspeed, vertical speed, angle of attack (AOA), lift, and power requirement and is considered severe when wind speeds change at rates greater than 500 feet a minute.
What Causes a Wind Shear?
Several things can cause a wind shear, including surface obstructions, weather fronts activity, temperature inversion and thunderstorms.
Surface obstructions, such as structures near an airport’s runway, mountains and trees, may cause the wind to vertically or horizontally spiral. Strong surface winds that blow through mountain ranges and mountain passes can cause severe wind shear when a plane is trying to land. These conditions are very unpredictable, but pilots should expect strong wind shears whenever there are strong surface winds.
Weather fronts also can impact the development of wind shear. People commonly hear about cold or warm fronts, but weather fronts generally speaking are areas where two air masses with different temperatures and densities meet. Specific front conditions are more conducive to wind shear, especially in fronts that move a speed of 30 knots or higher and those where temperature differences across the front at the surface are 10 degrees Fahrenheit (5C) or more. Because fronts are three-dimensional phenomena, you can experience frontal shear both horizontally and vertically. Vertical wind shear above warm fronts is more concerning than near and behind cold fronts because this occurrence lasts longer.
Temperature inversions occur when the temperature of the atmosphere increases with altitude in contrast to the normal decrease with altitude.
When temperature inversion happens, cold air underlies warmer air at higher altitudes. Temperature inversion may occur during the passage of a cold front or when a cooler onshore breeze invades sea air. Overnight radiative cooling of surface air often results in nighttime temperature inversion that disappears after sunrise when air warms near the ground. Large high-pressure systems lead to a longer-lasting temperature inversion, and descending currents of air near the center of the high-pressure system produce a warming, which causes air at middle altitudes to become warmer than the surface air. Pilots can expect a shear zone at the inversion if the wind at 2000 to 4000 feet AGL is 25 knots or more. To combat the effects of diminished headwind or increased tailwind at and below the inversion, you should allow a margin of airspeed above normal climb. However, turbulence may occur at the boundary between the inversion layer and the surrounding atmosphere. As the inversion dissipates, the shear plane and gusty winds move closer to the ground. However, in some areas of the Southwest it’s common to have a 90-degree change in direction and 20-to 30-knot increases in surface winds within a few minutes.
Lastly, gusty winds are caused when large downdrafts strike the ground and spread out horizontally. They also are associated with mature thunderstorms. These winds can change direction by as much as 180 degrees and reach velocities of 100 knots as far as 10 miles ahead of the storm. Thunderstorms can produce downbursts, which are an extremely intense, localized downdraft. This downdraft exceeds 700-feet-per-minute vertical velocity at 300 feet AGL. The power of the downburst can actually exceed aircraft climb capabilities, so it’s important to be mindful of these conditions when flying. Doing so will help to ensure you and everyone onboard is safe.