Definition
The series of steady white light bars that extend along the centerline of an Approach Lighting System (ALS) outward from the runway threshold, in the direction opposite to the landing aircraft's approach path. They form the lighted lead-in line that pilots follow visually toward the runway during the final segment of an instrument approach.
Plain English
Rows of white lights laid out in a line on the ground leading up to the start of the runway. Pilots use them to find and line up with the runway when breaking out of cloud or low visibility.
Context Anchor
Seen in approach lighting and visual descent guidance discussions, especially when reading about two-bar and three-bar visual approach slope indicator systems.
Derivation
‘Upwind’ in airport terminology refers to the direction beyond the departure end of the runway — the direction an aircraft heads after takeoff into the wind. The light bars sit on the approach end, which is upwind relative to the landing aircraft's flight path. ‘Bar’ here just means a short row of lights grouped together, not a single lamp.
Why Pilots Care
These lights are often the first visual reference a pilot sees when descending out of cloud on an instrument approach. Identifying them correctly is what allows the pilot to legally and safely continue below decision altitude or minimum descent altitude to land.
Intuition Check
Do not read “upwind” as a changing label based only on today’s wind report. Here it describes the light bars farther along the runway in the landing direction, compared with the bars near the approach end.
Example Sentence 1
As we descended through 400 feet, the upwind light bars came into view and gave us a clear path to the runway threshold.
Example Sentence 2
In the briefing the instructor noted that the upwind light bars become visible first when breaking out of the clouds on a circling approach.