If you have ever flown a plane, you probably know what wind shear is. Even in clear skies, your flight can be interrupted by the disorienting effects of wind shear. When you least expect it, you can be thrown into an emergency situation as your aircraft thrashes against the violent wind gradient outside.
While this sounds scary, it doesn’t have to be. Wind shear is a nuisance for pilots, but it does not have to be a threat. When handled responsibly, even junior pilots can safely bypass this nuisance without breaking a sweat.
Have you always wanted to learn more about wind shear, but don’t want to sit through an hour-long geography lesson? If so, you’re in luck. Our experts put together a quick guide that breaks down everything you need to know about it. Read on and discover what wind shear is, and how to respond to it safely and effectively.
Wind Shear 101
When it comes to combating the effects of wind shear, it is important to first establish what wind shear is. First, let’s define shear. If you want a succinct shear meaning, the best explanation is that it refers to a strain in the structure of an object caused by external pressure. This sort of pressure is brought about by lateral shifting among the external object’s layers.
Sounds simple enough, right? No? Well, it isn’t easy to provide a plain and simple shearing definition. Instead, we find that examples work better.
In the context of aviation, shearing occurs when the direction of the wind changes drastically at a sharp angle. Typically, wind shear occurs when the wind changes direction at a right angle. When this occurs, the velocity (i.e. speed) of the wind changes dramatically as well. This causes the plane to turn unexpectedly and can destabilize the aircraft.
It is a lot easier to provide a wind direction definition than it is to provide one for wind shear. Wind direction simply refers to the direction from which the wind originates. For instance, westerly winds are winds that originate in the west and flow toward the east. Therefore, the wind is directed toward the east.
When wind shear conditions are present, wind direction is unpredictable. If the aircraft is headed north in northerly winds, a wear shear might cause the wind to erratically flow east. When this occurs with enough velocity, it can disorient pilots and even cause overpowering drafts.
Wind Shear Effects
Wind shear has many important effects on flight. In the field of aeronautics, every pilot and manufacturer of aircraft must be fully prepared to deal with the sudden onset of this disorienting nuisance. If caught off guard, it can stall aircraft if they find themselves in strong headwinds.
Landing an Aircraft
Landing an aircraft while experiencing the effects of wind shear is no easy task. As the aircraft descends and moves through the wind gradient, the airspeed will decrease while the sink rate will increase. This is a destabilizing condition that should be avoided whenever possible. If possible, it is sometimes wise to accelerate before contacting with the ground.
Turning an Aircraft
Turning an aircraft during wind shear is equally difficult. This is especially true of aircraft that make sharp turns when cruising at low altitudes, or when they are preparing to land. Planes with long wingspans should always avoid making turns during wind shear conditions, as the airspeed on each wing may become too varied. This can cause a complete loss of control, or an aerodynamic stall.
Wind Shear and Weather
Wind shear can occur no matter what the skies look like. However, they can also be a good indicator of rapidly-changing weather. For example, thunderstorms, hailstorms, and tornadoes all require the presence of wind shear. Without the gradient brought about by wind shear, these storm conditions cannot be sustained.
In most cases, wind shear is caused by a specific kind of interaction with the weather. For example, if the storm’s inflow of air becomes completely separated from its outflow during rainy weather. When this occurs, harsh wind shear is likely to arise.
Without wind shear, thunderstorms and other hazardous weather conditions are unlikely to last long. If you happen to encounter stormy skies without the presence of wind shear, it is likely that the storm will blow over once its outflow is exhausted. By contrast, stormy weather with intense wind shear is likely to cause significantly hazardous conditions and should be avoided whenever it is possible to do so safely.
Wind shear has a powerful effect on tropical storms and cyclones. Tropic storms are natural events that convert thermal energy (i.e. heat) into mechanical energy (i.e. force). They are caused, in part, by wind and temperature gradients in which the ocean surface is warm and the upper skies are cool.
Interestingly, tropical storms do not require wind shear to sustain themselves. Rather, wind shear has the opposite effect on tropical storms. This is because cyclones require a warm center core to intensify. When vertical wind shear is active, this can cause the warm core to break up and cause the conversion of heat into force to slow down.
Therefore, pilots caught in the grip of a tropical storm should always pay close attention to the presence of wind shear. If there is no wind shear, pilots may falsely assume that this phenomenon to be a good sign. However, it is the opposite. Cyclones and tropical storms without wind shear tend to last longer and be more intense.
Detecting Wind Shear
All modern commercial aircraft are equipped with on-board wind shear detection systems. This has become a legal requirement in the United States following a series of high-profile aviation accidents in the 1970s. This requirement was introduced by law in 1993 in response to 26 aircraft accidents caused by wind shear.
Thanks to wind shear detection technology, wind shear is now responsible for only one aviation crash every ten years. This is a major turnaround in aviation history, as wind shear was once a serious threat for all commercial aircraft.
Modern airborne wind shear detection and alert systems are fitted into all commercial aircraft. They use radar and other technologies to process weather metrics. In doing this, these systems are able to detect “microbursts”. A microburst is a fancy term used to describe vertical wind shear conditions at the microwave level.
Once detected, wind shear detection systems display warning alerts on the Navigational Display Unit and, in most cases, an alarm sounds in the cockpit. This piece of technology is one of the most important housed within the electronic flight instrument system. Today, wind shear detectors are responsible for saving lives every year.
Terminal Doppler Weather Radar (TDWR) is a radar system that uses “pencil beams” to detect erratic wind conditions across the United States. The TDWR system is in service in 45 locations in the continental U.S. and has a high degree of accuracy for detecting early pre-conditions of wind shear and precipitation.
The TDWR was developed in the 1990s by researchers at the Massachusetts Institute of Technology. The TDWR was designed to assist air traffic control stations. By providing real-time weather data with a fine range resolution, TDWR has contributed to far fewer accidents caused by wind shear.
Low-Level Alert System
Another important technology for detecting wind shear is the low-level wind shear alert system (LLWAS). The LLWAS is a ground system that picks up on the presence of wind shear within close range. The weather data is collected and processed by a series of computers that can provide critical warnings to air traffic control towers.
The LLWAS system was developed and implemented in the 1970s, however much the U.S. has now replaced this system with the Doppler Radar (TDWR). Regardless, the LLWAS system can provide complementary data to assist the Doppler Radar. In remote locations, the LLWAS is the only detection system in place.
What to Do
If you encounter wind shear, it is important to keep calm. In most cases, wind shear does not present a threat to the aircraft. However, if you are given a warning by an air traffic controller tower about the presence of wind shear, you should always refrain from taking off. This is because microbursts can occur close to sea level, which makes take-off dangerous.
In most cases, it is not advisable to change the flap or its configuration to avoid the shear. Instead, listen closely to the tower for directives. Typically, this involves modifying your speed brakes, rolling your wings, or climbing at an accelerated pace. To get the hang of this, it is important for every pilot to practice these maneuvers in simulation.
(Another flying challenge to look out for is airplane spin. Learn to Handle Airplane Spins)