Definition
The set of published or assigned altitudes used by aircraft operating under Instrument Flight Rules during the en route phase of flight, between the departure and arrival terminal areas. These altitudes are designed to provide adequate terrain and obstacle clearance, acceptable navigation signal reception, and separation from other IFR traffic. They include categories such as Minimum En Route Altitude (MEA), Minimum Obstruction Clearance Altitude (MOCA), Minimum Reception Altitude (MRA), Maximum Authorized Altitude (MAA), and Off-Route Obstruction Clearance Altitude (OROCA), each serving a specific safety or navigation purpose along an airway or route segment.
Plain English
These are the altitudes a pilot is allowed or required to fly while cruising under instrument rules, between leaving the departure airport area and arriving at the destination area. Each altitude type is set to keep the aircraft safely above terrain, within range of navigation signals, and clear of other traffic.
Context Anchor
You see IFR en route altitudes on IFR en route charts, in route planning, and in altitude clearances from ATC during the middle part of an instrument flight.
Derivation
"En route" comes from French, meaning "on the way." In aviation it refers to the middle portion of a flight — after departure procedures end and before arrival procedures begin. "IFR" identifies the rule set under which these altitudes apply.
Why Pilots Care
They ensure consistent terrain clearance, regulatory compliance, and safe navigation between waypoints or airports.
Grounding Statement
On an IFR flight, the en route altitude is the safe, planned height for the cruise portion of the route, not just any comfortable cruising height.
Intuition Check
Do not read “en route altitude” as simply the altitude you happen to cruise at. In IFR use, it means an altitude selected, published, or assigned for specific route safety and traffic-control reasons.
Example Sentence 1
While planning the cruise portion of the IFR flight, the pilot reviewed the published IFR en route altitudes for each airway segment to ensure terrain clearance and navigation coverage.
Example Sentence 2
ATC cleared the flight to maintain an IFR en route altitude of 8000 feet across the next airway segment.