Definition
A configuration of flashing lights installed along an approach path to guide aircraft visually toward the runway when the final approach course is offset, curved, or otherwise difficult to identify from a distance. The lights flash in sequence toward the runway, providing an unmistakable visual lead-in from the en route environment to the runway threshold.
Plain English
A line of flashing lights on the ground that points the way to the runway. The lights flash one after another in the direction of the runway, so a pilot approaching at night or in poor visibility can clearly see which way to go.
Context Anchor
Seen in airport lighting information, chart notes, and NOTAM contractions when an airport has special lights that guide aircraft toward the runway area.
Derivation
Lead-in' simply means guiding something into a destination — the lights lead the aircraft in to the runway. The acronym LDIN is shorthand used on charts and in NOTAMs.
Why Pilots Care
They increase safety by helping pilots maintain correct alignment during night or reduced-visibility approaches.
Intuition Check
Lead-in lights are not simply runway lights. They are lights that lead you toward the runway or airport area before you are lined up with it.
Example Sentence 1
The approach plate noted LDIN serving Runway 22, which helped the pilot pick up the airport visually from several miles out.
Example Sentence 2
The approach chart indicated that LDIN were installed and operational for the landing runway.