Definition
An FAA aeronautical chart designed for IFR navigation below 18,000 feet MSL, depicting Victor airways, navigation aids, intersections, minimum en route altitudes, controlling ATC frequencies, airports with instrument approaches, and other information needed to fly an instrument flight plan in the low altitude structure.
Plain English
A map for instrument pilots flying below 18,000 feet. It shows the airways, radio navigation stations, required altitudes, and ATC frequencies needed to follow an IFR route.
Context Anchor
Seen during IFR route planning and in-flight navigation. In the closed-airport context, a pilot may check this chart to see whether an airport is shown as closed or has changed status.
Derivation
Low Altitude refers to the airspace below 18,000 feet MSL, where these charts apply. En route comes from the French 'en route', meaning 'on the way' -- the chart covers the cruise portion of the flight, not departure or approach.
Why Pilots Care
These charts provide the essential route and facility information required to conduct safe low-altitude IFR navigation where most training and general aviation flights occur.
Intuition Check
“Low altitude” does not mean any flight that feels low to the pilot. Here it means the FAA’s lower IFR route charting system, generally used below 18,000 feet above sea level in the United States.
Example Sentence 1
Before departure, she pulled up the current Low Altitude En route chart to confirm the MEAs along her planned route.
Example Sentence 2
Before filing the IFR flight plan, she checked the Low Altitude En route chart for any temporary flight restrictions near the destination.