FIG ENR 1.1.5
Effects of a Geographical Constraint on a Runway’s Declared Distances

NOTE.

A runway’s RSA begins a set distance prior to the threshold and will extend a set distance beyond the end of the runway depending on the runway’s design criteria. If these required lengths cannot be achieved, the ASDA and/or LDA will be reduced as necessary to obtain the required lengths to the extent practicable.
Federal Aviation Administration Twentieth Edition
9. Low Level Wind Shear/Microburst Detection Systems
9.1 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.
9.1.1 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.
9.1.2 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.
NOTE.
Reference GEN 3.5, Paragraph 25, Microbursts.
9.1.3 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.
9.1.4 The WSP provides weather processor en-hancements 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.
9.1.5 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.
10. Braking Action Reports and Advisories
10.1 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.
10.2 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).
10.3 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.”
10.4
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.

11.
Runway Friction Reports and Advisories

11.1 Friction is defined as the ratio of the tangential force needed to maintain uniform relative motion between two contacting surfaces (aircraft tires to the pavement surface) to the perpendicular force holding them in contact (distributed aircraft weight to the aircraft tire area). Simply stated, friction quantifies slipperiness of pavement surfaces.
　
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