Multiple choice Four red lights on a PAPI indicate that the airport is shut for operations the aircraft is very much below the glide slope the aircraft should not land for some time the aircraft is on the glide slope Reveal answer Fill a bubble to check yourself B Correct answer Explanation Four red lights on a PAPI indicate the aircraft is well below the glide slope. This is a dangerous situation requiring immediate correction to increase the aircraft's descent angle and avoid obstacles short of the runway.