page_title: Runway visual range
section_title: Data reliability
hierarchical_section_title: Runway visual range / Measurement / Data reliability
caption_attribution_description: English: Diagram to illustrate that transmissometers do give true Runway Visual Range in variable conditions
context_page_description: In aviation, the runway visual range is the distance over which a pilot of an aircraft on the centreline of the runway can see the runway surface markings delineating the runway or identifying its centre line. RVR is normally expressed in feet or meters. RVR is used to determine the landing and takeoff conditions for aircraft pilots, as well as the type of operational visual aids used at airport.
context_section_description: Because IRVR data are localized information, the values obtained are not necessarily a reliable guide to what a pilot can actually expect to see. This can easily be demonstrated when obscuration such as fog is variable, different values can apply simultaneously at the same physical point.
  For example, a 2000 m runway could have reported touchdown, midpoint and rollout IRVR values of 700m, 400m and 900 m. If the actual RVR at the touchdown point (300 m from the threshold) is 700 m as reported, then a pilot could expect to see the light 700 m away, at the runway midpoint. If the pilot taxies to the midpoint and looks back through the same air mass, he or she must also be able to see the light at the touchdown point, but since the midpoint RVR is reported as 400 m, a light 700 m away must be invisible. Similarly, looking forward he or she cannot see the light in the rollout area, but according to the rollout RVR of 900m, the light there is visible and has already been so for the last 200 m.
caption: A diagram of how RVR could vary along the runway
exif: {}