Plain English Meaning

Small labeled boxes on en route charts that tell you which radio frequency to use to talk to Air Traffic Control while flying through that part of the sky.

Full Definition

Printed boxes on IFR en route charts that list the radio frequencies used to contact an Air Route Traffic Control Center (ARTCC, or 'Center') within a given sector of airspace. Each box identifies the controlling Center facility and the frequency or frequencies a pilot should use to reach the controller responsible for that area.

Context Anchor

Seen on IFR en route charts during instrument flight planning and while flying an , especially when changing from one air traffic control frequency to another.