Low altitude airway structure

Low Altitude Airway Structure: The airways serving aircraft operations up to but not including 18,000 feet MSL.

LOW ALTITUDE AIRWAY STRUCTURE- The network of airways serving aircraft operations up to but not including 18,000 feet MSL.
(See AIRWAY.)
LOW ALTITUDE ALERT, CHECK YOUR ALTITUDE IMMEDIATELY- ...

En route facilities ring. Depicted in the plan view of IAP charts, a circle which designates NAVAIDs, fixes, and intersections that are part of the en route low altitude airway structure.
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See also: Airport, ILS, Expect, Direct, Radar