AIM 

4/20/23 

FIG 4

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Effects of a Geographical Constraint on a Runway’s Declared Distances 

NOTE

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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. 

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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 Systems 

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. 

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Airport Operations