RVR

RVR, or Runway Visual Range, is the distance over which a pilot on the runway centerline can see the runway surface markings or lights. It is a key measure of current visibility for landing and takeoff operations and is used by pilots, air traffic controllers, and airport operators to assess safety margins under adverse weather conditions such as fog, rain, or snow.

Measurement and equipment

RVR is determined with instruments installed along the runway. The most common devices are transmissometers, which assess light transmission along a fixed path, and forward scatter meters, which estimate visibility by measuring scattered light. Some modern installations may use lidar or additional sensors to supplement data. In practice, RVR values may be reported for each runway end, and on long runways there may be separate values for touchdown zone, mid-point, and rollout.

Reporting and units

RVR values are typically included in weather reports (METAR and TAF). They are presented as R followed by the runway designation, a slash, and the visibility value in meters, often with a trend indicator: U for increasing, D for decreasing, and N for no change. Example formats include R27/0800U. While meters are standard in many regions, some areas historically used feet; modern aviation weather practice generally reports RVR in metric units, with regional variations possible.

Operational significance

RVR directly affects landing and takeoff decision making. It influences approach minimums, runway usage, and the activation of lighting and instrument approach procedures. Differences between touchdown, mid, and rollout RVR values can indicate uneven visibility along a runway, which may lead to restricted operations or runway changes during low-visibility conditions.

In summary, Runway Visual Range is a crucial, instrument-based measure of prevailing visibility for aviation safety, informing procedures and decisions across flight operations.