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Airport Operations

4−3−7. Low Level Wind Shear/Microburst

Detection Systems

Low Level Wind Shear Alert System (LLWAS),

Terminal Doppler Weather Radar (TDWR), Weather

System Processor (WSP), and Integrated Terminal

Weather System (ITWS) display information on

hazardous wind shear and microburst activity in the

vicinity of an airport to air traffic controllers who

relay this information to pilots.

a. LLWAS provides wind shear alert and gust front

information but does not provide microburst alerts.

The LLWAS is designed to detect low level wind

shear conditions around the periphery of an airport. It

does not detect wind shear beyond that limitation.

Controllers will provide this information to pilots by

giving the pilot the airport wind followed by the

boundary wind.


Wind shear alert, airport wind 230 at 8, south boundary

wind 170 at 20.

b. LLWAS “network expansion,” (LLWAS NE)

and LLWAS Relocation/Sustainment (LLWAS−RS)

are systems integrated with TDWR. These systems

provide the capability of detecting microburst alerts

and wind shear alerts. Controllers will issue the

appropriate wind shear alerts or microburst alerts. In

some of these systems controllers also have the ability

to issue wind information oriented to the threshold or

departure end of the runway.


Runway 17 arrival microburst alert, 40 knot loss 3 mile



AIM, Paragraph 7−1−26 , Microbursts

c. More advanced systems are in the field or being

developed such as ITWS. ITWS provides alerts for

microbursts, wind shear, and significant thunder-

storm activity. ITWS displays wind information

oriented to the threshold or departure end of the


d. The WSP provides weather processor enhance-

ments to selected Airport Surveillance Radar

(ASR)−9 facilities. The WSP provides Air Traffic

with detection and alerting of hazardous weather such

as wind shear, microbursts, and significant thunder-

storm activity. The WSP displays terminal area

6 level weather, storm cell locations and movement,

as well as the location and predicted future position

and intensity of wind shifts that may affect airport

operations. Controllers will receive and issue alerts

based on Areas Noted for Attention (ARENA). An

ARENA extends on the runway center line from a

3 mile final to the runway to a 2 mile departure.

e. An airport equipped with the LLWAS, ITWS, or

WSP is so indicated in the Chart Supplement U.S.

under Weather Data Sources for that particular


4−3−8. Braking Action Reports and


a. When available, ATC furnishes pilots the

quality of braking action received from pilots. The

quality of braking action is described by the terms

“good,” “good to medium,” “medium,” “medium to

poor,” “poor,” and “nil.” When pilots report the

quality of braking action by using the terms noted

above, they should use descriptive terms that are

easily understood, such as, “braking action poor the

first/last half of the runway,” together with the

particular type of aircraft.

b. FICON NOTAMs will provide contaminant

measurements for paved runways; however, a

FICON NOTAM for braking action will only be used

for non−paved runway surfaces, taxiways, and

aprons. These NOTAMs are classified according to

the most critical term (“good to medium,” “medium,”

“medium to poor,” and “poor”).

1. FICON NOTAM reporting of a braking

condition for paved runway surfaces is not

permissible by Federally Obligated Airports or those

airports certificated under 14 CFR Part 139.

2. A “NIL” braking condition at these airports

must be mitigated by closure of the affected surface.

Do not include the type of vehicle in the FICON


c. When tower controllers receive runway braking

action reports which include the terms medium, poor,

or nil, or whenever weather conditions are conducive

to deteriorating or rapidly changing runway braking

conditions, the tower will include on the ATIS

broadcast the statement, “BRAKING ACTION


d. During the time that braking action advisories

are in effect, ATC will issue the most recent braking

action report for the runway in use to each arriving

and departing aircraft. Pilots should be prepared for