FIG 4 − 3 − 6 Effects of a Geographical Constraint on a Runway’s Declared Distances 8/15/19 AIM  Airport Operations 4 − 3 − 12 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.