NBAA 2003
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Predictive Windshear System (PWS)
NBAA 2003
Predictive Windshear System 风切变预警系统
Civil Aviation Flight University of China 2
Predictive Windshear System (PWS)
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.
NBAA 2003
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.
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.
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PWS provides windshear detection with very few operational changes that will affect flight crews.
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.
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.
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The Principle of PWS
NBAA 2003
PWS uses wind velocity data gathered by a Doppler weather radar system to identify the existence of a windshear.
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 radar also turns on automatically before takeoff—using air-ground and takeoff thrust logic—to provide windshear coverage during takeoff roll, rotation, and climbout.