Definition
An IFR aeronautical chart that depicts the airway structure, navigation aids, intersections, minimum altitudes, and communication frequencies used for instrument flight below 18,000 feet MSL. Published by the FAA and revised on a regular cycle, it is the primary navigation reference for IFR flight in the low-altitude airspace structure.
Plain English
A specific kind of map used for instrument flying at lower altitudes. It shows the official routes, radio aids, and required altitudes that pilots use when flying on instruments below 18,000 feet.
Context Anchor
Seen in NOTAM Search and preflight briefing products when filtering notices for the route portion of a flight, especially when using low-altitude en route charts.
Derivation
Enroute' comes from the French 'en route,' meaning 'on the way.' 'Low altitude' distinguishes it from the High Altitude chart used at and above 18,000 feet MSL. So the name simply describes what it is: a chart for use while on the way, at the lower altitudes.
Why Pilots Care
Pilots consult these charts and their associated NOTAMs to maintain accurate routing and obstacle clearance on IFR flights below FL180.
Intuition Check
“Low altitude” does not mean simply flying close to the ground. Here it refers to the FAA’s lower en route system, generally below 18,000 feet mean sea level, used between airports.
Example Sentence 1
Before the IFR flight, she pulled up the current Enroute Low Altitude chart on her tablet to confirm the airway and minimum altitudes.
Example Sentence 2
Airway changes listed under Enroute Low Altitude affect the charts used for routes below 18,000 feet.