AIM
4/3/14
4−3−11
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−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, Microbursts, Paragraph 7
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 Airport/Facility Directory
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 or
airport management. The quality of braking action is
described by the terms “good,” “fair,” “poor,” and
“nil,” or a combination of these terms. 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”) used 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
ADVISORIES ARE IN EFFECT.”
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.
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9. Runway Friction Reports and
Advisories
a.
Friction is defined as the ratio of the tangential
force needed to maintain uniform relative motion
between two contacting surfaces (aircraft tires to the