AIM

8/15/19

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Airport Operations

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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

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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

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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

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

REFERENCE

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AIM, Paragraph 7

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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
runway.

d.

The WSP provides weather processor enhance-

ments to selected Airport Surveillance Radar
(ASR)

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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

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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