A PAPI (Precision Approach Path Indicator) is a single row of four lights next to the runway. Which configuration indicates the aircraft is on the correct glide path?

Why →A PAPI uses a single row of four lights. On the correct glide path the two lights nearest the runway read red and the two farthest read white, giving two red and two white. All white means too high, and all red means too low. Remote pilots do not fly PAPI approaches, but the aid appears on the Part 107 knowledge test.

The trap →More white means higher, more red means lower. Four white is well above the path and four red is well below it. The balanced two red and two white is the only on-path indication.

Field note →A simple recall: "white on high, red on low, two of each and on you go." PAPI resolution is finer than a two-bar VASI, which is why most modern runways use it.