How many different light combinations do PAPI and VASI provide, and what are their arrangements?

How many different light combinations do PAPI and VASI provide, and what are their arrangements?

• A. PAPI 3, VASI 5; PAPI vertical; VASI horizontal
• B. PAPI 5, VASI 3; PAPI vertical; VASI horizontal
• C. PAPI 5, VASI 3; PAPI horizontal; VASI vertical
• D. PAPI 4, VASI 4; PAPI horizontal; VASI vertical

Answer: (C)

PAPI and VASI convey glide path by patterns of color across a small number of lights, but they use different numbers of patterns and different physical layouts. PAPI uses four lights in a single horizontal row. Each light can be white or red, giving five distinct recognizable patterns as you descend: all white, three white and one red, two white and two red (on the slope), one white and three red, and all red. The horizontal row makes this single, easy-to-read sequence visible to the pilot. VASI uses two bars of lights stacked vertically (two lights per bar). This arrangement yields three standard patterns that correspond to high, on the glide path, or low. The result is three combinations, with a vertical two-bar layout. So the best description is five combinations for PAPI in a horizontal arrangement, and three combinations for VASI in a vertical arrangement.

PAPI and VASI convey glide path by patterns of color across a small number of lights, but they use different numbers of patterns and different physical layouts.

PAPI uses four lights in a single horizontal row. Each light can be white or red, giving five distinct recognizable patterns as you descend: all white, three white and one red, two white and two red (on the slope), one white and three red, and all red. The horizontal row makes this single, easy-to-read sequence visible to the pilot.

VASI uses two bars of lights stacked vertically (two lights per bar). This arrangement yields three standard patterns that correspond to high, on the glide path, or low. The result is three combinations, with a vertical two-bar layout.

So the best description is five combinations for PAPI in a horizontal arrangement, and three combinations for VASI in a vertical arrangement.