Definition
Special low-visibility taxi charts published for airports that have an approved Surface Movement Guidance and Control System (SMGCS) plan. The diagrams show the specific taxi routes, lighting, hold positions, and signage that pilots and controllers must use when runway visual range (RVR) is below 1,200 feet. They are used in addition to the standard airport diagram, not in place of it.
Plain English
When fog or weather makes the airport very hard to see, certain busy airports switch to special taxi maps that show exactly which paths to follow on the ground. These maps are the SMGCS visual aid diagrams, and pilots use them whenever visibility drops below the published threshold.
Context Anchor
Seen in airport low-visibility taxi procedures and in discussions of how pilots move safely between the runway, taxiways, and ramp when visibility is poor.
Derivation
SMGCS stands for Surface Movement Guidance and Control System. 'Visual aid' simply means a tool you look at to help you find your way, like a map. So the name describes what the diagram is: a picture-based tool for guiding aircraft on the surface when normal visual cues are obscured.
Why Pilots Care
They allow safe ground navigation on complex airports when fog or darkness removes normal visual references.
Analogy
Think of them like a bad-weather driving map for the airport surface: when you cannot see far ahead, the diagram helps you match each sign, light, and painted line to where you are supposed to go.
Grounding Statement
The diagrams convert the airport's physical layout into a step-by-step visual path a pilot can follow on the ground.
Intuition Check
Do not read this as a general picture or illustration. In SMGCS use, a visual aid diagram is a practical airport surface guide for low-visibility taxi movement.
Example Sentence 1
With the RVR reported at 800 feet, the crew pulled out the SMGCS visual aid diagram before requesting taxi clearance.
Example Sentence 2
The diagrams confirmed that all hold-short markings along the route were properly lighted and marked.