FIG 7-1-16

Warning Boxes

(b) LLWAS was fielded in 1988 at 110 airports across the nation. Many of these systems have
been replaced by new TDWR and WSP technology.
Eventually all LLWAS systems will be phased out;
however, 39 airports will be upgraded to the
LLWAS-NE (Network Expansion) system, which
employs the very latest software and sensor
technology. The new LLWAS-NE systems will not
only provide the controller with wind shear warnings
and alerts, including wind shear/microburst detection
at the airport wind sensor location, but will also
provide the location of the hazards relative to the
airport runway(s). It will also have the flexibility and
capability to grow with the airport as new runways are
built. As many as 32 sensors, strategically located
around the airport and in relationship to its runway
configuration, can be accommodated by the
LLWAS-NE network.
3. Terminal Doppler Weather Radar (TDWR).
(a) TDWRs are being deployed at 45 locations across the U.S. Optimum locations for TDWRs
are 8 to 12 miles off of the airport proper, and
designed to look at the airspace around and over the
airport to detect microbursts, gust fronts, wind shifts

Meteorology

and precipitation intensities. TDWR products advise
the controller of wind shear and microburst events
impacting all runways and the areas 1/2 mile on either
side of the extended centerline of the runways out to
3 miles on final approach and 2 miles out on
departure.
(FIG 7-1-16 is a theoretical view of the warning
boxes, including the runway, that the software uses in
determining the location(s) of wind shear or
microbursts). These warnings are displayed (as
depicted in the examples in subparagraph 5) on the
RBDT.
(b) It is very important to understand what
TDWR does NOT DO:
(1) It DOES NOT warn of wind shear
outside of the alert boxes (on the arrival and departure
ends of the runways);
(2) It DOES NOT detect wind shear that is
NOT a microburst or a gust front;
(3) It DOES NOT detect gusty or cross
wind conditions; and
(4) It DOES NOT detect turbulence.
However, research and development is continuing on
these systems. Future improvements may include
such areas as storm motion (movement), improved

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