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6/17/21 

AIM 

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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. 

EXAMPLE

 

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. 

EXAMPLE

 

Runway 17 arrival microburst alert, 40 knot loss 3 mile 
final. 

REFERENCE

 

AIM, Para 7

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24 , 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 
runway. 

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 
airport. 

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8.  Braking Action Reports and 

Advisories 

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 
NOTAM. 

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 

ADVISORIES ARE IN EFFECT.” 

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 

Airport Operations 

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