Vector Wind Shear

Weather plays a significant role in aviation safety, it is regularly referred to as the biggest contributing factor in accidents and incidents. Wind shear in the form of microbursts can be a severe hazard to any aircraft during take-off, approach, and landing¹. The latest generation of flight planning tools must be highly reliable in regard to wind shear calculations in order to ensure flight safety. With that in mind, RocketRoute has developed a new highly accurate approach to wind shear calculation.

What is 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 the wind over either horizontal or vertical distances. Turbulence may also be associated with wind shear, and this is an additional hazard².

Typical Wind Shear Hazardous Scenarios³

• An aircraft on the initial climb encounters a microburst with strong down-drafts, which prevent the aircraft from climbing away, even though the pilot immediately recognizes the wind shear and takes the correct actions.
• An aircraft on approach in head-wind conditions encounters horizontal wind shear resulting in a change of wind component to tail-wind; the aircraft touches down late and fast and overshoots the runway.

Why Wind Shear Calculation is Important and How It's Done

Wind shear is important as it can impact the safety of a flight. In the upper atmosphere, the main concern is turbulence, while at lower altitudes – particularly during landing/takeoff – the primary consideration is the avoidance of accidents caused by increases in wind shear.

In the past (and on many current legacy systems) the calculation was done by comparing forecast wind speeds above and below a chosen Flight Level. However, using the scalar method means that a 50kt wind at 0 degrees below a selected flight level, and a 50kt wind at 180 degrees above the flight level would give a scalar wind shear value of ZERO. Therefore a vector (velocity) calculation (speed and direction) gives a much more useful result and can be accomplished using modern methods.

The wind shear value shown in the route results may be used as a combined arbitrary scale of smoothness of flight and general risk to the aircraft.  Routes may be sorted by this new column, for example, if the main passenger requirement is a very smooth flight experience.

How Wind Shear is Calculated in RocketRoute

RocketRoute FlightPlan provides a simple scale that works globally, from 0 to 30.

On a recent GFS data set maximum vector wind shear values were obtained globally for all flight levels. The table below can be used to understand the scale that our new calculation derives from the GFS data. Sample data set from 08 Sep 2020. 

Maximum values over the entire globe for different FLs: 

Difference between scalar and vector method of wind calculation. The below screenshot shows where the vector wind shear result per route is displayed.

References

1. Wind Shear: An Invisible Enemy to Pilots?

2. Wind Shear and Its Impact on Flight Operations: Part 1 – Definitions

3. Skybrary: Typical scenarios