Wind Shear and Its Impact on Flight Operations: Part 1 – Definitions
This business aviation blog post is part of a two-part series on wind shear.
For business aircraft operators, wind shear has the potential to cause flight turbulence and sudden increases/decreases in both ground and air speed, as well as other associated violent air movements. It’s always best to talk with your 3rd-party provider or aviation meteorologist to confirm the potential impact of any expected wind shear for your trip.
The following is an overview of what you need to know:
1. Importance of wind shear
Wind shear is important as it can impact the safety of your flight. In the upper atmosphere, the main concern is turbulence, while at lower altitudes – particularly during landing/takeoff – the primary consideration is avoidance of accidents caused by increases in wind shear.
2. Defining wind shear
Wind shear – a variation in wind speed and direction over a relatively short distance in the atmosphere – is also known as "wind gradient." Wind shear refers to variations in wind over either horizontal or vertical distances. Turbulence may also be associated with wind shear, and this is an additional hazard.
3. Vertical and horizontal wind shear
Wind shear can occur horizontally or vertically although the most common type is vertical. Horizontal wind shear usually involves directional changes, particularly when crossing a front. While vertical wind shear may involve both directional and speed changes. Vertical wind shear typically has a greater impact on airspeeds.
4. Where this occurs
Wind shear conditions can occur at low or high altitudes – anywhere there’s wind. Horizontal wind shear is most frequently experienced when crossing fronts or flying in the vicinity of mountainous areas. Vertical wind shear can be experienced anywhere from the surface to upper Flight Levels (FLs) – particularly with associated thunderstorm conditions. The most dangerous conditions are when flying at lower levels, due to proximity of the surface and potential for accidents. At higher altitudes the negative effects of wind shear are mostly related to turbulence.
5. Measuring wind shear
Wind shear is always measured in knots, with the values being either positive or negative. Increases in wind shear value are positive numbers, while decreases are noted as negative values. When operating in the upper atmosphere, wind shear value is almost always positive. Closer to the surface, you may experience negative wind shear values.
6. Sample wind shear value calculation for a flight plan
|Flight Level (FL)||Wind Speed|
|380 (FL above opt FL)||52|
|370 (optimum cruising FL)||48|
|360 (FL below opt FL)||42|
The difference in wind speed between one FL above optimal cruising altitude (52) and the one below optimum cruising altitude (42) is used to determine wind shear. The difference between the two is 10. This value (10) is then divided by 2 to account for the 2,000-ft. change in altitude. As a result the vertical wind shear is reported as "5."
Wind shear information is normally a part of a standard weather briefing provided with a flight plan. Wind shear values are not provided on weather charts, so it’s best to talk with a weather provider prior to your flight. Your weather provider will review various weather models to give you better insight into wind shear-related activity, including potential for flight turbulence.
If you have any questions about this article or would like weather assistance for your next trip, contact me at firstname.lastname@example.org.
Stay tuned for Part 2, which covers different considerations pertaining to wind shear.