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AIM

10/12/17

7−1−51

Meteorology

FIG 7−1−16

Warning Boxes

(b) LLWAS was fielded in 1988 at 110 air-

ports 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been replaced by new TDWR and WSP technology.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 (TD-

WR).

(a) TDWRs are being deployed at 45 loca-

tions 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

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