Definition
The greatest horizontal distance at which a pilot can see and identify prominent unlighted objects by day, or prominent lighted objects by night, when looking along the surface. In the context of Runway Visual Range (RVR), it is the horizontal distance a pilot will see down the runway from the approach end, derived from transmissometer measurements near the touchdown zone.
Plain English
How far you can see straight ahead along the ground or down the runway, rather than how high you can see up into the sky.
Context Anchor
Seen in runway visual range and low-visibility takeoff or landing discussions.
Derivation
"Horizontal" comes from the Latin horizon, meaning the boundary line where earth meets sky -- so horizontal visual range is sight measured along that flat line, not upward or downward.
Why Pilots Care
Determines whether visibility meets the minimums required to continue an approach and land.
Grounding Statement
On a foggy runway, horizontal visual range is the distance ahead before runway lights or markings fade from view.
Intuition Check
Do not read range here as a radio navigation aid or a general area. Here it means seeing distance along a level path, such as down a runway.
Example Sentence 1
The transmissometer near the touchdown zone reports the horizontal visual range a pilot can expect when landing.
Example Sentence 2
When horizontal visual range drops below 1800 feet, the approach minimums are no longer met.