Aeronautical Information Manual (AIM), page 212

Index   211 -- Page 212 -- 213


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 7-1-25 , 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 or
airport management. The quality of braking action is
described by the terms "good," "fair," "poor," and
"nil," or a combination of these terms. Effective

October 1, 2016, these terms will be replaced with

"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. For NOTAM purposes, braking action reports

are classified according to the most critical term

("fair," "poor," or "nil"). Effective October 1, 2016,

these terms will be replaced with "good," "good to
medium," "medium," "medium to poor," "poor," and
"nil" and issued as a NOTAM (D).

c. When tower controllers have received runway

braking action reports which include the terms 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 latest braking action
report for the runway in use to each arriving and
departing aircraft. Pilots should be prepared for
deteriorating braking conditions and should request
current runway condition information if not
volunteered by controllers. Pilots should also be
prepared to provide a descriptive runway condition
report to controllers after landing.

4-3-12 Airport Operations

Page 212 of the Aeronautical Information Manual (AIM.pdf)
AIM: Official Guide to Basic Flight Information and ATC Procedures

Index   211 -- Page 212 -- 213