Definition
On an instrument approach chart plan view, a NAVAID information box drawn with a thick (heavy) border, indicating that the navigation aid inside the box is the primary facility used for the published approach procedure. NAVAIDs shown in thin-lined boxes on the same chart are secondary or supporting facilities.
Plain English
It is the box on the approach chart with a thick black outline. The thick outline is a visual signal telling the pilot, 'this is the main navigation aid for this approach.'
Context Anchor
Seen in the plan view of FAA instrument approach charts, near the symbol for the navigation facility.
Derivation
NAVAID is a shortened form of “navigational aid,” meaning a facility or system that helps an aircraft navigate. “Heavy-lined” simply means the box is drawn with a thicker line than ordinary chart boxes, which signals that the facility has special importance to the procedure.
Why Pilots Care
Allows quick identification of the navigation aid's type and available equipment for route and approach planning.
Intuition Check
Do not read “heavy-lined” as decoration or emphasis only. On an FAA approach chart, the thicker box is a chart signal that the NAVAID is tied to the procedure.
Example Sentence 1
During the approach briefing, the pilot identified the VOR shown in the heavy-lined NAVAID box as the primary facility and tuned it first.
Example Sentence 2
A heavy-lined box on the enroute chart showed the navigation aid also provided DME.