现在飞机的气象雷达大多都加装了PWS预测风切变功能。飞机的GPWS近地警告系统也提供低空风切变警告。判断原理是多普勒频移原理。飞机顶风产生正的多普勒频移，顺风产生负的多普勒频移，如果在一个很短的距离内探测到明显的正负风速变化，则可判断为风切变。机组得到风切变警告后需立即采取措施，比如停止近进，复飞，风切变机动飞行，来躲开风切变。起飞和复飞时，飞机的自动驾驶系统会提供飞行指引，帮助机组进行正确的俯仰操作。进近时，如果遭遇严重风切变，机组应该脱开自动驾驶，进行人工飞行，否则有可能失速。不操纵飞机的驾驶员要密切监视垂速表和高度表，机组的快速反应和清醒的意识是非常重要的。

Windshear is a sudden, rapid change in wind velocity or direction. It is often found in –– but is not limited to –– thunderstorms or other highly unstable atmospheric events.

The most dangerous form of windshear is known as microburst, a vertical column of air rapidly descending toward the ground.

Upon reaching the ground, microburst spreads out horizontally, creating a horizontal outflow.

Entering a microburst is very dangerous for an airplane because the wind may be strong enough to overcome the maximum of climb performance.

Known as the Predictive Windshear System (PWS), this technology permits weather radar systems to scan the atmosphere ahead of an airplane and detect windshear before the airplane enters it.

Predictive Windshear System (PWS)

The Principle of PWS

PWS uses wind velocity data gathered by a Doppler weather radar system to identify the existence of a windshear.

Radar energy is emitted through the airplane's radome in order to gather atmospheric information such as wind speed and direction. The weather radar receiver/transmitter then uses this information, in addition to air data and inertial data, to determine the presence of a windshear.

The weather radar processor identifies wind velocity characteristic that indicate a rapid change in wind velocity or direction over a relatively small area. When the magnitude of the detected windshear reaches a predetermined intensity level, the system alerts the flight crew.

If the PWS detects a windshear from a significant distance, the flight crew may be able to avoid it completely. If windshear is unavoidable, however, PWS gives the flight crew valuable time to increase speed or altitude before the airplane enters a windshear.

The Principle of PWS

PWS provides windshear detection with very few operational changes that will affect flight crews.

First, the flight crew does not need to manually turn on the weather radar for it to operate in the windshear mode.

If not already turned on by the flight crew, the radar automatically turns on at 2,300 feet (700m) above ground level (AGL) for approach and landing coverage.

The radar also turns on automatically before takeoff—using air-ground and takeoff thrust logic—to provide windshear coverage during takeoff roll, rotation, and climbout.

The flight crew can manually activate PWS on the ground by turning on the weather radar. The automatic activation of PWS does not affect the weather radar display; it will remain in the mode and range selected by the flight crew.

The Principle of PWS

The PWS automatically sets weather radar gain and tilt when in a windshear mode. As a result, it is effective regardless of the settings made by the flight crew on the weather radar control panel.

Crew-selected tilt and gain are used when the radar is in a weather sweep. PWS requires a dedicated sweep of the weather radar to detect windshear.

If the flight crew uses the weather radar below 2,300 feet (700m) AGL, the radome will alternate between normal weather radar sweeps and PWS sweeps.

The Principle of PWS

Figure 11.1

Weather Radar Control Panel

The Principle of PWS

Predictive Windshear System has an effective range of three nautical miles ahead of the airplane.

At typical approach speeds of Boeing airplanes, the radar gives a detected windshear alert from 10 to 70 seconds before windshear entry.

The level of alert given to the flight crew depends on the position of the detected windshear threat relative to the airplane.

PWS：power system/ power subsystem 电源系统/ 电源适配器

在计算机，尤其是计算机硬件中，PWS与ADA (Adapter)一样，指代电源适配器。