SECTION 2: CHAPTER 5 PREVAILING VISIBILITY

Question 1

Prevailing visibility is defined as

Answer 1

the visibility value that is reached or exceeded within at least half the horizon circle or within at least half of the surface of the aerodrome. These areas could comprise contiguous or non-contiguous sectors.

Question 2

The prevailing visibility at an observing station will always be reported. Where the visibility in any direction is…

Answer 2

less than the prevailing visibility and less than 1500 metres or less than 50% of the prevailing visibility, the lowest visibility observed will also be reported. The general direction of the area of lower visibility will be 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 will be reported.
2.2 When the visibility is fluctuating rapidly and the prevailing visibility cannot be determined, only the lowest visibility will be reported, with no indication of direction.

Question 3

When verbally passing a report of visibility, e.g. as part of the aerodrome weather report passed to a pilot, the visibility should be transmitted as in current reports and without reference to the term prevailing visibility. An example is shown below for reference:

Answer 3

METAR EGxx 1250 1800 0800NE … should be transmitted as “Weather at one two five zero, visibility one thousand eight hundred metres, eight hundred metres to the North East ….”
3.2 Certain ATC procedures are implemented during specific visibility conditions. When two visibility values are present in a report, the lower of the two values shall be used to determine whether to implement such procedures.