Definition
The visibility, expressed in statute miles or fractions of a mile, within a specified sector or arc of the horizon as observed from a given point, typically a control tower or weather observation station. It is reported when visibility differs noticeably from one direction to another.
Plain English
How far you can see when looking in one particular direction, rather than an average all the way around. It's used when the view is clearer in some directions than others.
Context Anchor
Seen in airport weather observations, weather remarks, and pilot weather briefings when fog, rain, snow, smoke, or haze affects one direction more than another.
Derivation
Sector' comes from the Latin 'sectus,' meaning 'cut.' A sector is a 'cut' or slice of the full circle of the horizon. So sector visibility is the visibility within one slice of the view around the observer.
Why Pilots Care
Determines whether takeoff or landing minimums are met in the direction of the runway or approach path.
Grounding Statement
Sector visibility is about one direction, not the whole airport area.
Intuition Check
Do not assume sector visibility is the same as the airport’s overall reported visibility. It is visibility for one direction or slice of the horizon.
Example Sentence 1
The tower reported prevailing visibility of five miles, but sector visibility to the north was only one mile due to a passing snow shower.
Example Sentence 2
The pilot checked sector visibility toward the departure runway before accepting the clearance.