Definition
The depicted boundaries on an IFR en route chart that show where controlled airspace begins, ends, or changes, including lateral edges and floors of Federal airways, Class E airspace, and other controlled segments. Beyond these limits, ATC separation services and IFR clearances are not provided in the same way.
Plain English
The lines on the chart that show where the airspace ATC controls stops or changes. Inside the limits, ATC is watching over and separating IFR traffic. Outside, that protection ends or changes form.
Context Anchor
Seen on IFR en route low altitude charts when identifying the boundary of controlled airspace along a route.
Derivation
“Limit” comes from an older word meaning a boundary or edge. That helps here because the phrase is not mainly about restrictions; it is about the edge of a defined area of airspace.
Why Pilots Care
Knowing these limits tells a pilot exactly when they must contact ATC, obtain a clearance, or follow IFR rules instead of basic VFR.
Intuition Check
Do not read “limits” as meaning performance limits or restrictions. Here it means boundaries. Do not read “controlled” as meaning the airplane is being controlled. It means the airspace is managed under ATC rules.
Example Sentence 1
The chart legend showed the limits of controlled airspace as a shaded line, helping the pilot see where the Class E floor stepped down to 1,200 feet AGL.
Example Sentence 2
Once outside the limits of controlled airspace, the flight could proceed under VFR without an ATC clearance.