Definition
The lowest published altitude on a Victor airway, jet route, or other charted route segment that meets obstacle clearance requirements for the entire segment, but only assures acceptable navigation signal coverage from the route's navigation aids within 22 nautical miles of the station. Pilots may use this altitude only within 22 NM of the VOR.
Plain English
The lowest altitude you are allowed to fly on a charted route that still keeps you safely above terrain and obstacles for the whole segment, but is only valid when you are within 22 nautical miles of the navigation station.
Context Anchor
Seen on IFR en route charts and in instrument route planning, often shown as MOCA for a segment between fixes.
Derivation
Obstruction clearance' is the key part: this altitude is built around clearing obstructions along the route, while sacrificing the longer-range navigation signal guarantee that the standard minimum enroute altitude provides.
Why Pilots Care
Allows safe IFR flight on published routes at a lower altitude than the MEA when navigation signal coverage is assured close to a VOR.
Grounding Statement
Think of it as the charted floor for obstacle safety on a specific instrument route segment.
Intuition Check
“Clearance” does not mean an ATC clearance here; it means safe vertical space above obstacles. “Minimum” does not mean the best altitude to fly; it means the lowest published altitude that still meets the obstacle-clearance requirement.
Example Sentence 1
Within 20 miles of the VOR, the pilot descended to the MOCA shown on the chart to stay below the cloud layer while remaining clear of terrain.
Example Sentence 2
Although the MEA was 6000 feet, the MOCA of 4500 feet was sufficient within 22 miles of the VOR.