Terminal Windshear Systems
Ching-Huei Hsu (Jeff ), a visiting
engineer from the CAA in Taipei, is working on the AOAWS MDS display at the Boulder
lab.
From an operational perspective, the
AOAWS windshear detection component provides two major functions: 1) to improve safety by
providing tactical decision making information to pilots for windshear events, and 2) to
provide strategic meteorologists at the weather stations for use in decision-making for
optimizing terminal efficiency and capacity. Because airspace is limited, especially
during bad weather, it will be important to utilize all available AOAWS information in
order to optimize operations.
Maximizing the utility of the AOAWS
windshear components will be a function of how the system is ultimately used in an
operational environment and this will be governed by its capabilities and performance.
Convective Windshear and Microburst
Products
Microbursts are well recognized as
an aviation hazard. Until the U.S. TDWR and Enhanced LLWAS systems were developed and
implemented, no explicit microburst alerts were available. Onboard reactive windshear
devices now provide windshear alerts to help pilots recognize that they have entered a
windshear event, but they are reactive and do not provide an alert that can help pilots
avoid windshear before they enter the event. Forward-looking systems are now just coming
into operation and these will provide alerts of a minute or two ahead of entering
windshear events. The ground-based systems (TDWR and LLWAS), which define microbursts as
windshears with peak-to-peak windspeed differences of > 30 kts over distances
< 2.5 nm, have microburst probabilities of detection (PODS) > 90% and false alarm
rates (FARs) < 10%. Due to the high performance, the U.S. airlines have developed the
policy that aircraft operations (approaches or departures) must cease if a
"microburst alert" is given by these systems. When the TDWR or LLWAS systems
generate a "windshear-with-loss alert", which is defined as a peak-to-peak
windspeed difference of 15-29 kts over a distance of < 2.5 nm, it is up to
the pilot to determine whether to continue operating.
Convective windshear events and
microbursts typically last about ten minutes. This short duration is due to a combination
of the true life cycle of the events coupled with the fact that they are usually moving
with the precipitation cells. At times when the precipitation cells are moving more slowly
(< 20 kts), the windshear events may impact the airport operations for a longer period.
The avoidance of the hazard is an obvious safety benefit; however, every delayed departure
and missed approach will disrupt the traffic flow and hence, impact capacity (if airspace
is limited). The geographical information provided to the air traffic supervisors and
managers on the GSD provides an opportunity to see the "bigger picture" and
minimize disruptions.
Advanced Operational Aviation
Weather System (AOAWS) in Taiwan 
