Plain English Meaning

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.

Full 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.

Context Anchor

Seen on IFR en route low altitude charts when identifying the boundary of controlled airspace along a route.