Definition
The lowest published altitude on a Victor airway, off-airway route, or route segment that meets obstacle clearance requirements for the entire segment. MOCA assures the standard obstacle clearance (1,000 feet in non-mountainous terrain, 2,000 feet in designated mountainous terrain) but only assures acceptable navigation signal coverage from the relevant VOR within 22 nautical miles (25 statute miles) of that VOR.
Plain English
The lowest altitude you can fly along a route that still keeps you safely above terrain and obstacles, but where the navigation signal is only guaranteed to work within 22 nautical miles of the VOR.
Context Anchor
Seen on IFR en route low altitude charts along airways or route segments, often shown with an asterisk before the altitude.
Derivation
Built from plain English — 'minimum' (the lowest acceptable), 'obstacle clearance' (staying above terrain and structures), and 'altitude.' The name describes exactly what the number guarantees: clearance from obstacles, nothing more.
Why Pilots Care
It lets you descend lower than the MEA when necessary while still maintaining safe obstacle clearance and navigation reception.
Grounding Statement
MOCA answers the question: “How low can I be on this route segment and still have required protection from obstacles?”
Intuition Check
Do not read “clearance” here as an ATC clearance. In MOCA, “clearance” means safe vertical separation from terrain and obstacles.
Example Sentence 1
Unable to maintain the MEA due to icing, the crew requested a descent to the MOCA for that segment and stayed within 22 NM of the VOR.
Example Sentence 2
On the chart the MOCA of 4500 feet allowed the flight to remain below the clouds while staying clear of terrain.