Far 135.385
I took the following from the FAA's Aviation Safety Inspector Handbook (Operations), FAA Order 8400.10 ...
LANDING FIELD LENGTH REQUIREMENTS
FAA Order 8400.10, CHG 5, (6/30/91) Volume IV, Chapter 3, Section I – Airplane Performance Computation Rules
/S/ 909 SMALL AIRPLANE CERTIFICATION.
E. Application of Flight Handbook Performance Limits. Many of the requirements of Subparts I of part 121 and Part 135 apply only until the aircraft takes off from the departure point. Other requirements from these Subparts apply at all times as do the AFM limitations. For example, FAR 121.195 and FAR 135.385 prohibit a large, turbine airplane from takeoff unless, allowing for en route fuel burn, the airplane will be capable of landing on 60% of the available runway at the planned destination. The regulations do not, however, prohibit the airplane from landing at the destination when, upon arrival, conditions have changed and more than 60% of the runway is required. In this case, the airplane must only be able to land on the effective runway length as shown in the flight manual performance data.
/S/ 921. WATER AND CONTAMINATION OF RUNWAYS. AFM performance data is based on a dry runway. When a runway is contaminated by water, snow, or ice, charter AFM performance values will not be obtained. Manufacturers typically provide guidance material to operators so that appropriate corrections for these conditions may be applied to performance calculations. Inspectors should be aware of the following guidance concerning these conditions.
A. Any runway which is not dry is considered to be wet. Standing water, puddles, or continuous rain are not necessary for a runway to be considered wet. Runway braking friction can change when there is a light drizzle. In some cases, even dew or frost which changes the color or a runway will result in a significant change in runway friction. The wet-to-dry stopping distance ratio on a well-maintained, grooved, wet runway is usually around 1.15 to 1. On a runway where the grooves are not maintained and rubber deposits are heavy, the stopping distance ratio could be as high as 1.9 to 1. On un-grooved runways, the stopping distance ratio is usually about 2 to 1. In the case of a runway with new pavement or where rubber deposits are present, the ration could be as high as 4 to 1. Some newly-surfaced asphalt runway surfaces can be extremely slippery when only slightly wet.
/S/ 933. LANDING DISTANCE. The maximum weight for an airplane landing on any runway must be limited so that the landing distance required by the performance rules will be less than the effective landing length available.
A. Effective Landing Runway Length. Effective landing runway lenght for all categories of airplanes is the distance from the point on the approach end of the runway at which the obstruction plane intersects the runway to the roll-out end of the runway. [read as “Threshold”, not glide slope intersect, ed.] The obstruction plane is a plane that is tangent to the controlling obstruction in the obstruction clearance area that slopes down toward the runway at a 1:20 slope from the horizontal. The area in which the obstruction clearance plane must clear all obstacles is 200 feet on each side of the runway centerline at the touchdown point, which expands to a width of 500 feet on each side at a point 1.500 feet from the touchdown end and beyond. The centerline of the obstruction clearance area may curve at a radius of not less than 4,000 feet, but the last 1,500 feet to the touchdown point must be straight in. Stopways are not usually considered, and clearways may not be considered, as available landing areas.
TransMach
