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AIM

10/12/17

7−1−39

Meteorology

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 7−1−6.)

TBL 7−1−6

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

g. Ten minute maximum and minimum RVR

values for the designated RVR runway are reported in

the body of the aviation weather report when the

prevailing visibility is less than one mile and/or the

RVR is 6,000 feet or less. ATCTs report RVR when

the prevailing visibility is 1 mile or less and/or the

RVR is 6,000 feet or less.

h. Details on the requirements for the operational

use of RVR are contained in FAA AC 97−1, Runway

Visual Range (RVR). Pilots are responsible for

compliance with minimums prescribed for their class

of operations in the appropriate CFRs and/or

operations specifications.

i. RVR values are also measured by forward

scatter meters mounted on 14−foot frangible

fiberglass poles. A full RVR system consists of:

1. Forward scatter meter with a transmitter,

receiver and associated items.

2. A runway light intensity monitor (RLIM).
3. An ambient light sensor (ALS).
4. A data processor unit (DPU).
5. Controller display (CD).

j. The forward scatter meter is mounted on a

14−foot frangible pole. Infrared light is emitted from

the transmitter and received by the receiver. Any

obscuring matter such as rain, snow, dust, fog, haze

or smoke increases the amount of scattered light

reaching the receiver. The resulting measurement

along with inputs from the runway light intensity

monitor and the ambient light sensor are forwarded to

the DPU which calculates the proper RVR value. The

RVR values are displayed locally and remotely on

controller displays.

k. The runway light intensity monitors both the

runway edge and centerline light step settings (steps 1

through 5). Centerline light step settings are used for

CAT IIIb operations. Edge Light step settings are

used for CAT I, II, and IIIa operations.

l. New Generation RVRs can measure and display

RVR values down to the lowest limits of

Category IIIb operations (150 feet RVR). RVR

values are displayed in 100 feet increments and are

reported as follows:

1. 100−feet increments for products below

800 feet.

2. 200−feet increments for products between

800 feet and 3,000 feet.

3. 500−feet increments for products between

3,000 feet and 6,500 feet.

4. 25−meter increments for products below

150 meters.