Definition
The amount of distance, measured in degrees, by which a pilot must begin a turn before reaching a VOR radial in order to roll out established on that radial. The lead compensates for the aircraft's turn radius at its current groundspeed and bank angle.
Plain English
How early you start your turn so you finish lined up on the radial you want, instead of overshooting it.
Context Anchor
Seen in radial engine maintenance, ignition inspections, and troubleshooting for rough engine operation.
Derivation
From 'radial' (a line outward from a VOR station) and 'lead' (in the sense of leading a target — starting an action early so the result lines up correctly). The same 'lead' idea appears in shooting and sailing: you don't aim where the target is, you aim where it will be.
Why Pilots Care
Correct routing and condition of radial leads ensures reliable spark delivery and prevents misfiring or engine roughness in flight.
Intuition Check
Do not read lead here as the metal “lead” or as “being ahead.” In this term, a lead is an electrical wire that carries current.
Example Sentence 1
At 120 knots groundspeed in a standard-rate turn, the pilot used a small radial lead to roll out cleanly on the 270 radial inbound to the VOR.
Example Sentence 2
A broken radial lead on cylinder five caused a noticeable drop in RPM during the magneto check.