Definition
The lowest published altitude on a Federal airway, jet route, or other direct route segment that guarantees both acceptable navigation signal coverage and required obstacle clearance between the two fixes that define that segment.
Plain English
The lowest altitude you are allowed to fly along a particular section of an airway. At or above this altitude, your navigation signals will work properly and you will safely clear the terrain and obstacles below.
Context Anchor
Seen on instrument flight route charts along airways and other charted route segments.
Derivation
From Latin 'minimum' (smallest), Old French 'route' (a way or course), and French 'en route' (on the way). Together: the smallest altitude you may use while on the way along a charted route.
Why Pilots Care
It guarantees both reliable navigation and terrain clearance so pilots can fly the published route without losing signal or hitting obstacles.
Grounding Statement
If a route segment shows an MEA of 6,000 feet, that segment has been evaluated for obstacle clearance and navigation reception at or above 6,000 feet.
Intuition Check
Do not read “minimum” as “best” or “recommended.” Here it means the lowest published altitude that still meets the required obstacle-clearance and navigation-coverage standards for that route segment.
Example Sentence 1
The MEA for that airway segment is 8,000 feet, so the controller cleared us to climb before crossing the fix.
Example Sentence 2
The chart showed an MEA of 4000 feet between the two fixes, so the flight stayed at or above that altitude.