Plain English Meaning

Specific parts of the country the FAA has officially marked as mountainous because the ground rises and falls steeply. Flying in these areas requires extra altitude buffers to keep aircraft safely above terrain.

Full Definition

Geographic regions designated by the FAA where terrain elevation changes by more than 3,000 feet within a horizontal distance of approximately 10 nautical miles. These designated areas are depicted on FAA charts and trigger higher obstacle clearance requirements for instrument procedures, minimum en route altitudes, and off-route obstruction clearance altitudes.

Context Anchor

Seen in design , route planning, and discussions of near terrain.