AIM
4/20/23
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Meteorology
and, therefore, offer greater freedom of action. In terminal areas, the problem is more acute because of traffic
density, ATC coordination requirements, complex departure and arrival routes, adjacent airports, etc. As a
consequence, controllers are less likely to be able to accommodate all requests for weather detours in a terminal
area or be in a position to volunteer such routing to the pilot. Nevertheless, pilots should not hesitate to advise
controllers of any observed severe weather and should specifically advise controllers if they desire
circumnavigation of observed weather.
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13. Runway Visual Range (RVR)
There are currently two configurations of RVR in the NAS commonly identified as Taskers and New Generation
RVR. The Taskers are the existing configuration which uses transmissometer technology. The New Generation
RVRs were deployed in November 1994 and use forward scatter technology. The New Generation RVRs are
currently being deployed in the NAS to replace the existing Taskers.
a.
RVR values are measured by transmissometers mounted on 14
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foot towers along the runway. A full RVR
system consists of:
1.
Transmissometer projector and related items.
2.
Transmissometer receiver (detector) and related items.
3.
Analog recorder.
4.
Signal data converter and related items.
5.
Remote digital or remote display programmer.
b.
The transmissometer projector and receiver are mounted on towers 250 feet apart. A known intensity of
light is emitted from the projector and is measured by the receiver. Any obscuring matter such as rain, snow, dust,
fog, haze or smoke reduces the light intensity arriving at the receiver. The resultant intensity measurement is then
converted to an RVR value by the signal data converter. These values are displayed by readout equipment in the
associated air traffic facility and updated approximately once every minute for controller issuance to pilots.
c.
The signal data converter receives information on the high intensity runway edge light setting in use (step 3,
4, or 5); transmission values from the transmissometer and the sensing of day or night conditions. From the three
data sources, the system will compute appropriate RVR values.
d.
An RVR transmissometer established on a 250 foot baseline provides digital readouts to a minimum of 600
feet, which are displayed in 200 foot increments to 3,000 feet and in 500 foot increments from 3,000 feet to a
maximum value of 6,000 feet.
e.
RVR values for Category IIIa operations extend down to 700 feet RVR; however, only 600 and 800 feet
are reportable RVR increments. The 800 RVR reportable value covers a range of 701 feet to 900 feet and is
therefore a valid minimum indication of Category IIIa operations.
f.
Approach categories with the corresponding minimum RVR values. (See TBL 7
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7.)
TBL 7
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Approach Category/Minimum RVR Table
Category
Visibility (RVR)
Nonprecision
2,400 feet
Category I
1,800 feet*
Category II
1,000 feet
Category IIIa
700 feet
Category IIIb
150 feet
Category IIIc
0 feet
* 1,400 feet with special equipment and authorization