TERPS Visibility Segment
FINAL APPROACH SEGMENT: This is the segment in which alignment and descent for landing are accomplished. The final approach segment considered for obstacle clearance begins at the Final Approach Fix (FAF) and ends at the runway or missed approach point(MAP) whichever is encountered last. Final approach may be made to a runway for a straight-in landing or to an airport for a circling approach.
Standard Alignment: The visual area is aligned with the runway centerline extended.
Standard Length: The visual area begins 200 feet from the runway threshold (THR) at the THR elevation and extends 10,000 feet along track of the runway centerline extended at a 20:1 slope. Note the visual segment begins 200 feet from the runway threshold not from 200 feet in front of the runway end the defined Part 77 obstacle approach surface.
How to Calculate
Standard Width: The beginning width of the visual area is 400 feet (200′ either side of runway centerline). The sides splay outward relative to runway centerline. Calculate the width of the area at any distance “d” from its origin using the following formula:
1/2W = (0.15d) + 200
Where 1/2W = Perpendicular distance from centerline to edge of area.
Where d = Distance (ft) measured along track (centerline from area origin.