I had the advantage of being able to look at multiple areas of the airport and had predetermined landmarks aiding me in identifying how far I could see. I would determine the greatest horizontal visibility equaled or exceeded throughout at least half the horizon circle not necessarily continuously and that would be the prevailing visibility.
If the transmissometer which senses visibility was wrong I would override it and publish the actual prevailing visibility. Although augmented weather observations are better than automated ones they are still not good enough for operations in extremely poor weather conditions. RVR is the best way a pilot can know exactly what the visibility is going to be directly over the runway.
It is used primarily for operations in very low visibility so you will often see RVR equipment at large airports with lots of airline or jet traffic. The transmissometer projector and receiver are mounted on towers feet apart. A known intensity of light is emitted from the projector and measured by the receiver. In the case of RVR the light signal may be obscured by matter such as rain, snow, dust, fog, haze or smoke.
The intensity of the light is measured by the receiver and converted to an RVR value by the signal data converter. An RVR transmissometer established on a foot baseline provides digital readouts to a minimum of feet.
These setups are currently being phased out. According to FAA Order The new systems have low maintenance costs, eliminate the use of steel and concrete structures on the airport surface, and provide RVR readings as low as 0 feet. Ten-minute maximum and minimum RVR values for the designated RVR runway are reported in the body of an aviation weather report when the prevailing visibility is less than 1 mile or the RVR is 6, feet or less.
Runway visual range is coded in the following format: the initial R is code for runway and is followed by a runway number. When more than one runway is defined with the same runway number a directional letter is coded on the end of the runway number.
RVR values are coded in increments of feet up to 1, feet, increments of feet from 1, feet to 3, feet, and increments of feet from 3, to 6, feet. When the RVR varies by more than one reportable value, the lowest and highest values will be shown with V between them indicating the variable conditions. If RVR is lower than its lowest reportable value, the visual range group is preceded by an M. If RVR is greater than its highest reportable value, the visual range group is preceded by a P.
Air traffic control will also be able to provide a pilot with RVR divided into thirds of the runway so that a pilot will be able to know what to expect at touchdown, mid runway, and rollout.
Runway visual range is a very useful tool that pilots can use at airports with the proper equipment. Another RVR element, the ambient light sensor ALS , is used to interpret the impact that background lighting, such as nearby runway lights, might have on the overall visibility measurement. Normally two ALSs are installed in central locations relative to the airfield environment.
Next, the runway light intensity monitor, or RLIM, establishes the proper intensity of a high-intensity runway lighting system in varying visibilities, based on data from the ALS. Eventually, data from all the sensor elements finds its way to the data processing unit, the main RVR computer, where the final calculations are performed to create the RVR readout placed in front of a tower or radar-room controller.
Menu Sign Up. It's calculated using sensors like this:. The sensors are located along the runway, and they're approximately 14 feet higher than the centerline of the runway. On most runways equipped with RVR, there are three sensors: a touchdown sensor, a mid-point sensor, and a rollout sensor.
While it's good to know about the sensors, it's even better to be able to actually read RVR. So let's jump into that. RVR is only reported at airports that have RVR sensing equipment, when the visibility is 1 statue mile or less, or when RVR for an instrument runway is 6, feet or less. Screenshots taken from our Aviation Weather Products online course. In this example, "" indicates the RVR for runway 18R is feet.
The increments that RVR visibility is described in also changes as the visibility gets lower. The lower the visibility, the smaller the increments that RVR is reported:. If visibility is less than the lowest reportable RVR value, an "M" is placed in front of it. And if the visibility is greater than the highest reportable value, a "P" is placed in front of it.
And when RVR varies by more than one reportable value over a minute period, the lowest and highest values are paired with a "V" between them. In this example, "V", indicates the RVR for runway 18R is varying between feet and feet. But GA pilots like us can use it too. While there aren't any visibility minimums under Part 91 to begin an approach, RVR can give you a general idea if you're going to be able to see the runway or approach lights at minimums.
In the chart below, the blue highlighted "24" is short for feet RVR minimum visibility for the approach.
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