Definition
The altitude at which a pilot begins the level-off from a climb or descent so the aircraft arrives smoothly at the target altitude without overshooting. A common rule of thumb is to begin the level-off at roughly 10 percent of the vertical speed before reaching the assigned altitude (for example, lead by about 50 feet when descending at 500 feet per minute).
Plain English
The altitude where you start leveling off, a little before the altitude you're actually trying to reach, so the aircraft settles right on it instead of flying past.
Context Anchor
Used during instrument climbs and descents when preparing to level off at an assigned or selected altitude.
Derivation
"Lead" here is used in the sense of "starting early" -- the same way a hunter leads a moving target, or a driver brakes before a stop sign. You begin the action ahead of the point you actually want to hit.
Why Pilots Care
Using the correct lead altitude prevents altitude deviations that can trigger altitude alerts or violate assigned altitudes during instrument flight.
Analogy
It is like starting to brake before a stop sign instead of waiting until the car is already at the sign. The earlier action helps you arrive smoothly at the exact place you intended.
Intuition Check
Lead altitude is not the altitude where you intend to fly level. It is the earlier altitude where you begin the level-off so you arrive at the intended altitude accurately.
Example Sentence 1
Descending at 700 feet per minute toward 5,000 feet, the pilot used a lead altitude of 5,070 feet to begin the level-off.
Example Sentence 2
During the climb, the student applied a 100-foot lead altitude so the airplane would level exactly at 4,000 feet without overshooting.