Definition
The lowest published altitude on an airway segment that guarantees both acceptable navigation signal coverage and required obstacle clearance between the two navigation fixes that define that segment.
Plain English
On any given stretch of an airway, this is the lowest altitude you are allowed to fly that still keeps you safely above terrain and obstacles and still lets your navigation equipment receive a usable signal.
Context Anchor
Seen during instrument preflight planning on en route charts when choosing safe altitudes for each part of the route.
Derivation
From Latin minimum ("the smallest") and French en route ("on the way"). The phrase literally describes the smallest altitude that is acceptable while underway between two fixes.
Why Pilots Care
Flying below this altitude risks loss of navigation signals or collision with terrain.
Intuition Check
Do not read “minimum” as “a good low altitude to use if convenient.” Here it means the lowest published altitude that still meets specific safety and navigation requirements for that route segment.
Example Sentence 1
The MEA for the next airway segment was 8,000 feet, so the pilot requested a climb before crossing the fix.
Example Sentence 2
ATC cleared the aircraft to climb to the minimum en route altitude after the initial departure fix.