On a PAPI display, what pattern indicates the aircraft is on the correct glide slope?

• A. Two white lights and two red lights.
• B. Three white lights.
• C. Four green lights.
• D. Two white lights and two red lights.

Answer: (D)

PAPI uses color-coded cues to show your vertical position relative to the glide slope. The four lights indicate whether you’re on, above, or below the optimal path. When you’re on the glide slope, the pattern you want to see is two white lights and two red lights, which signals you’re exactly at the correct descent angle. If you’re above the glide slope, more lights appear white (three or four), and if you’re below it, more lights appear red (three or four). Green lights aren’t part of a standard PAPI indication, so seeing four green lights would not represent being on the slope.