It would appear from the following, that the maximum range would be defined per the specific installation...
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Runway Visual Range (RVR) is a term used in
aviation meteorology to define 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
metres.
RVR is used as one of the main criteria for minima on
instrument approaches, as in most cases a pilot must obtain visual reference of the runway to land an aircraft. The maximum RVR reading is 2,000 metres or 6,500 feet, above which it is not significant and thus does not need to be reported. RVRs are provided in
METARs and are transmitted by
air traffic controllers to aircraft making approaches to allow pilots to assess whether it is prudent and legal to make an approach.
Originally RVR was measured by a person, either by viewing the runway lights from the top of a vehicle parked on the runway threshold, or by viewing special angled runway lights from a tower at one side of the runway. The number of lights visible could then be converted to a distance to give the RVR. This is known as the
human observer method and can still be used as a fall-back.
Today most airports use
Instrumented Runway Visual Range or IRVR, which is measured by devices called
transmissometers which are installed at one side of a runway relatively close to its edge. Normally three are provided, one at each end of the runway and one at the mid-point.
A transmissometer is an instrument for measuring the
extinction coefficient of the
atmosphere, and for the determination of
visual range. It operates by sending a narrow,
collimated beam of energy (usually a
laser) through the
propagation medium. A narrow
field of view receiver at the designated measurement distance determines how much energy is arriving at the
detector, and determines the path
transmission and/or extinction coefficient. Atmospheric extenction is
wavelength dependent phenomenon, but the most common wavelength in use for transmissometers is 550
nm, which is right in the middle of the visible waveband, and allows a good approximation of visual range.
Transmissometers are sometimes referred to as
telephotometers, transmittance meters, or
hazemeters.