Definition
Radials shown on an instrument approach chart that mark the point at which a pilot should begin a turn from one course or arc to the next, accounting for the aircraft's turn radius so the rollout occurs on the new course.
Plain English
A radial drawn on the chart that tells you when to start your turn, so you don't overshoot the new course when you roll out of the turn.
Context Anchor
Seen on the plan view of some instrument approach charts, especially where a curved path around a navigation station connects to another course.
Derivation
"Lead" here means "to begin ahead of" — the same sense used when a hunter leads a moving target. The radial is positioned ahead of the actual course change so that, by the time the turn finishes, the aircraft is established on the new course.
Why Pilots Care
Starting the turn at the correct point produces a smooth, stabilized intercept and prevents overshooting the final approach course.
Intuition Check
Do not read “lead radial” as just another course to fly. The important idea is advance warning: it marks where to start the turn, not necessarily where to keep flying straight.
Example Sentence 1
As we flew the DME arc inbound, the chart showed a lead radial about seven degrees before the final approach course, so we began the turn there to roll out on course.
Example Sentence 2
Lead radials are especially helpful when the arc radius or groundspeed requires an earlier turn than the final approach course itself.