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Chapter 14 | Hazard Avoidance Systems
Predictive Wind-Shear Warning System (PWS) The predictive wind-shear warning system, installed as part of an aircraft’s weather radar system, detects probable wind shear ahead of the aircraft and alerts the flight crew with both visual and aural warnings. The predictive wind shear component of the weather radar collects wind-velocity data to identify the existence of wind shear. Remember that radar is not a weather detector, but rather a water detector. Therefore, moisture must be present in the disturbed airflow or the PWS will not detect wind shear. Most predictive wind shear warning systems are designed to operate automatically. This means that regardless of the cockpit weather radar control panel settings, PWS will turn itself on, adjust the antenna tilt and even adjust the receiver gain. Since wind shear encounters are most dangerous in departure and arrival situations near the ground, PWS is automatically enabled when the engine thrust levers are advanced for take-off, and again on approach when the aircraft descends below 2,300 feet AGL. PWS provides a visual depiction of wind-shear areas on the pilot’s HSI. One of the more common systems uses red-and-black cross-hatching to display the areas to avoid. This visual warning is accompanied by an aural warning voice stating, “Wind shear ahead! Wind shear ahead!” Wind shear warning systems have been installed on advanced aircraft for many years. The original wind shear warning systems relied on components of the GPWS system to detect and warn of windshear encounters at the instant they happened. Such systems are now called reactive wind-shear warning systems because they deliver no warning until you actually encounter wind shear. Many advanced aircraft contain both reactive and predictive windshear warning systems (Figure 14.14).
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Predictive wind-shear symbol shows wind shear location correlated to radar precipitation returns.
Pilot’s Navigation Display
FIGURE 14.14 | Predictive wind-shear warning system
(PWS) display.
