Definition
A visual landing aid located beside the runway that uses a row of light units to show the pilot whether the aircraft is on, above, or below the correct glide path on final approach. Each light appears either white or red depending on the angle from which it is viewed, and the combination seen by the pilot indicates the approach angle relative to the ideal descent path to the runway.
Plain English
A small set of lights next to the runway that tells you, by changing colour, if you are coming in too high, too low, or just right.
Context Anchor
Seen during landing, especially on final approach when aligning with the runway and checking descent path.
Derivation
Named for what it does: it precisely indicates the approach path. The word 'precision' signals that it gives finer information than older two-bar systems, with four light units producing a clearer picture of how far off the glide path the pilot is.
Why Pilots Care
Correct glide path guidance reduces the chance of landing short or floating long, improving landing safety and consistency.
Analogy
Like a set of traffic lights that turn different colors depending on whether your car is too high or low relative to an invisible line.
Intuition Check
PAPI does not fly the airplane or give steering commands. It is a visual reference that shows whether your descent path is high, low, or on track.
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
The instructor pointed out that all red PAPI lights meant the approach was too low and needed an immediate correction.