Have you ever seen “R14/1800” on a METAR and wondered what it meant? When the surface visibility gets low, runway visual range values may be included on the automatic terminal information service. These values provide accurate visibility along various points on the runway for use during takeoff and landing.
Using a device known as a transmissometer, runway visual range (RVR) is calculated at either end of the runway as well as the midpoint. This provides data for touchdown, midpoint, and rollout for either runway direction. These values range from 500 feet to more than 6,000 feet and usually are measured and reported only when the surface visibility is below one statute mile.
The standard visibility value required for departure is one statute mile for aircraft with two engines or fewer. With specific runway lighting installed and operational, such as high-intensity runway lights and centerline lights, you can depart with as little as 500 feet of RVR. This allows aircraft to depart with considerably less visibility, resulting in fewer delays and cancellations of private and commercial flights.
These advantages are also available for instrument approaches; when authorized, a Category 1 ILS approach can be flown to as low as 1,800 RVR in certain circumstances (if flown with the use of a flight director, autopilot, or HUD). Standard approach minimums for a Category I ILS are one-half mile visibility, which would equal approximately 2,600 feet (2,400 feet RVR). By utilizing RVR values and operable runway lighting, it’s possible to land with visibility lower than the standard.
How is this a safe and legal way to take off and land with reduced visibility? Automated weather reports measure visibility from where the facility is located on the airport, or it’s reported by an observer in the tower. These values are important, but sometimes they don’t accurately reflect what the visibility is on or down the runway. By measuring the visibility in the immediate vicinity of the runway, and at multiple points along the runway, the visibility values generated are considered more accurate than those from a surface visibility report. There are many scenarios in which reporting stations can be substituted for other inoperative ones, or when all are required, or when only one is required—or any combination of those. Know and understand not only the regulations mandated by the FAA but also company operating specifications.
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