Visibility minima are not considered beyond 5000M. In case value of visibility minima exceeds 5000M after addition of 200m to normal minima, it is to be considered as 5000M only,
8. Methods for Reporting Visibility
Following methods are used to report the visibility:
i. General Visibility or Met Visibility reported by the Met Observer by estimation method i.e., by identifying the well known land marks around the airport and reports the lowest visibility.
In case, a) When the lowest visibility is different from the prevailing visibility, and less than 1500m or less than 50% of the prevailing visibility, the lowest visibility observed should also be reported and its general direction relation to the aerodrome indicated by reference to one of the eight points of the compass. If the lowest visibility is observed in more than one direction, then the most operationally significant direction should be reported; and
b) When the visibility is fluctuating rapidly, and the prevailing visibility cannot be determined, only the lowest visibility should be reported, with no indication of direction.
The usage of prevailing visibility is preferred to minimum visibility as it gives a better representation of visibility of operations, especially in the planning stage, and does not restrict operations when the lowest visibility was not affecting the runways and approaches. The usage of prevailing visibility has some operational implications also. With the use of minimum visibility, the visibility encountered by the pilots was equal or more than that given in the reports. But if we use prevailing visibility, the visibility encountered could be less than
Pg-10/28 the reported value in most situations. As per ICAO recommendations, lowest visibility could be reported, when the visibility is varying rapidly and prevailing visibility cannot be assessed. These facts are to be kept in mind while reporting and interpreting prevailing visibility.
ii. Instrumental Visibility (RVR/AVRA): In marginal weather conditions visibility along the runway is estimated by the instrument commonly known as RVR/AVRA, installed near the runway. RVR/AVRA have been installed at most of the Rwy equipped with ILS Cat I system and RVR is reported whenever visibility reduces to 1500M or below.
iii. Runway Direction Visibility or Manual RVR: If RVR/AVRA is unserviceable, manual RVR may be reported by counting Rwy edge lights from the Rwy threshold. Generally, these lights are installed at 60M interval along the Rwy.
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