6.1.2.2. WIND SHEAR DETECTION
Two kinds of protection are provided against wind shears:
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The Predictive Wind Shear (PWS) performed by the weather radar to avoid wind shear events,
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The Reactive Wind Shear performed by the flight controls to escape from wind shear events.
Appendix H – Low level Wind shear effects on aircraft performances summarizes
the effects of wind shears on aircraft performances.
6.1.3. WEATHER RADAR OPERATING MODES
According to the weather radar manufacturer, several operating modes are available. Based on the radar principle, the weather radar is able to detect:
- Weather (or more precisely wet precipitations)
- Turbulence (except Clear Air Turbulence)
- Wind shears
- The ground.
From one manufacturer to another, the operating modes may vary. As a general rule, the different operating modes are defined for de-cluttering purposes (i.e. superimposition of different layers of information).
6.1.3.1. WX MODE
The weather radar detects wet precipitations up to 320 NM and provides a coded-color display according to their precipitation rates. Refer to 6.1.1.4 – Gain for the color code.
6.1.3.2. WX+T, WX/TURB OR TURB MODE
In addition to weather, the weather radar detects and displays turbulence (except Clear Air Turbulence) in magenta. The detection of turbulence is limited to a range of 40 NM.
The detection of turbulence (as well as wind shears) is based on the Doppler principle. Indeed, the weather radar detects an area as turbulent if velocities of water droplets are above 5 m/s and the area presents high variations in velocities. The weather radar will not consider an area where water droplet velocities are quite homogeneous as turbulent.
The left part of Figure 6-17 shows a wide spectrum of velocities but the numbers of returns for each velocity are quite homogeneous. The variation of velocities is smooth.
The right part of Figure 6-17 shows a wide spectrum with a heterogeneous distribution of velocities. The variation of velocities is irregular and causes turbulence.
The WX+T (Rockwell Collins) or the WX/TURB (Honeywell) combines weather and turbulence information for display. The TURB mode (Rockwell Collins) only shows turbulence information for a better identification of turbulent areas.
6.1.3.3. MAP MODE
- In addition to weather, the weather radar also displays ground returns. The colors indicate the various levels of altitude/strength of return of the object
(e.g. water is a good reflector and may appear red). It may permit mainly to distinguish peaks from valleys in mountainous regions, but with no guarantee on the quality of the data.
6.1.3.4. PWS MODE
The Predictive Wind Shear (PWS) supplements the Reactive Wind Shear (refer to
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