What is PAPI and how does its color encode vertical guidance?

• A. A radar-based landing aid
• B. An instrument that reports wind
• C. A security beacon
• D. A four-light visual descent aid; color patterns indicate whether you are high or low on the glide path.

Answer: (D)

PAPI is a four-light visual descent aid that gives you vertical guidance through color patterns. The lights are arranged so that, when you’re on the correct glide path, you see two white lights and two red lights. If you’re higher than the glide path, more lights appear white; if you’re lower, more lights appear red. This quick color cue helps you adjust your descent to stay on the intended glide slope, typically about 3 degrees. It’s not a radar, wind instrument, or security beacon, but a simple visual aid to keep you on vertical profile during final approach.