Definition
A system of lights installed beside a runway that gives the pilot a visual indication of whether the aircraft is on, above, or below the correct glide path during the final approach to landing. A standard PAPI consists of a single row of four lights, each of which appears either white or red depending on the angle from which it is viewed. The combination of red and white lights tells the pilot the aircraft's vertical position relative to the published approach slope, typically 3 degrees.
Plain English
A row of four lights next to the runway that shows you, by their colors, whether you're coming in too high, too low, or just right.
Context Anchor
You see a PAPI beside the runway during the final part of an approach, and you may see it listed in airport information or mentioned when airport lighting is not working.
Derivation
"Precision" indicates the system gives an accurate reading of glide path angle, not just a rough "high or low" indication. "Indicator" means it shows the pilot information rather than controlling anything. Together: a precise visual tool for staying on the correct descent path.
Why Pilots Care
Ensures pilots maintain the proper descent angle to avoid runway undershoot or overshoot.
Grounding Statement
On final approach, the PAPI gives a quick red-and-white visual cue that helps you adjust your descent before landing.
Intuition Check
Do not read “precision approach” here as meaning an instrument precision approach. A PAPI is a visual runway lighting aid, not a complete instrument approach system.
Example Sentence 1
On final approach, the pilot saw two white and two red lights on the PAPI, confirming the aircraft was on the correct glide path.
Example Sentence 2
During night operations, the PAPI provides essential visual cues for a stabilized approach.