This business aviation blog continues from our article last week, entitled “Wind Shear and Its Impact on Flight Operations: Part 1 – Definitions.”

For business aircraft operators, wind shear can have significant impact during takeoff/landing due to its effect on control of the aircraft. Wind shear can be the sole or one of the contributing causes of many aircraft accidents. Low-level/surface-level wind shear is caused mostly by thunderstorm and frontal system activity, while, at higher flight levels, wind shear is usually related to jet stream and frontal activity.

The following is an overview of what you need to know:

1. Wind shear on a flight plan is not a turbulence value

There’s often confusion regarding wind shear and shear values as they relate to flight turbulence. This is due to misconceptions about the relationship between wind shear value and turbulence. A wind shear number is simply a numerical value of differences in wind speeds between flight levels. This value does not necessarily predict turbulence. To determine potential for turbulence associated with wind shear, it’s best to speak with a 3rd-party provider, aviation meteorologist, or flight dispatcher. They’ll look at wind shear values – along with satellite imagery, weather models, and other data – to help determine if potential for turbulence exists. There are different types of turbulence, and the impact of this turbulence depends on your type of aircraft. Maximum takeoff weight, wingspan, and wing loading all impact aircraft performance in relation to wind shear and susceptibility to turbulence. The military, for example, usually calculates predicted turbulence based on the type of aircraft.

2. Relevance of wind shear values

Wind shear values help determine the possibility of turbulence being experienced in flight, but these values are not true indicators of potential of turbulence. It’s best not to rely on wind shear values alone in terms of predicting turbulence. Wind shear should, instead, be used as an indicator to look further into the potential for flight turbulence.

3. Wind shear scales

There are no pre-determined scales used for wind shear, but each operator will typically have his or her own comfort zone. For example, an operator may stipulate that any wind shear value over five requires the crew to be notified and obtain an in-depth weather briefing based on their route and time of flight. There are times of year and regions of the world where wind shear values tend to run particularly high. A good example is traveling over the Newfoundland area during winter and in the presence of strong jet stream activity. Here, wind shear values of eight-10 can be the norm.

4. Wind shear and aircraft type

The main reason there’s no pre-determined scale for wind shear is that wind shear does not necessarily correlate to flight turbulence. The reason for this is because turbulence experienced on a particular trip depends so much on the type of aircraft.

5. Clear air turbulence

Clear Air Turbulence (CAT) is usually based on jet stream activity. Calculation of wind shear values can help try to identify CAT. It’s important to note, though, that, while wind shear may cause CAT, wind shear and CAT are not the same.

6. Obtaining forecast wind data

Forecast wind data is normally published every six hours and can be found from reliable sources such as the U.S. National Weather Service or the UK MET. The closer the forecast data is to the actual time of flight, the more accurate the data will be in terms of predicted conditions you’ll encounter. Be mindful that forecast wind model data can change greatly between the times it’s published. For flight planning purposes, it’s suggested to run flight plans based on historical winds, well in advance, followed by test flight plans a day or two ahead of the estimated time of departure. Particularly for longer (seven-hour plus) flights, the crew should obtain latest wind data as close as possible to time of departure.

Conclusion

It’s important to understand how wind shear may impact your flight. Best practice is to obtain a weather brief day of flight and to talk with a meteorologist to better understand potential wind shear-related issues. Keep in mind that wind shear is only an indicator of flight turbulence and does not necessarily mean that you’ll experience actual flight turbulence. Type of aircraft will be a key consideration in turbulence experiences from shear.

Questions?

If you have any questions about this article or would like weather assistance for your next trip, contact me at jasonplowman@univ-wea.com.