When conducting a visual approach in a Cat C aircraft (B737) the distance (4.2NM) is measured from the threshold of all usuable runways (over 1800m). When you have a 3000m runway the the areodrome reference point is in the middle of the runway (best case), that's not going to work.Regardless runway thresholds can be used as a waypoints, it says so in the manual. Its also useful to put a 10 mile ring from the threshold to help situational awarness, ie at 10 miles should be 3000ft. Matt