What is VASI and how does it differ from PAPI?

• A. Visual Approach Slope Indicator; older two-bar system; generally less precise than PAPI.
• B. Runway Visual Alignment System; provides glide path alignment.
• C. Precision Approach Path Indicator; color-coded lights indicate deviations.
• D. Visual Aiming System Indicator; modern system offering greater precision than PAPI.

Answer: (A)

VASI stands for Visual Approach Slope Indicator. It’s an older glide-slope indicator that uses two light bars to give you a visual cue of your descent path toward the runway. Because it’s a two-bar setup, the information you get about how far off the proper path is less precise than what you get with newer systems. PAPI, on the other hand, stands for Precision Approach Path Indicator and uses a 2-by-2 array of lights, which provides finer gradations of deviation from the glide slope. That greater resolution lets pilots make smaller, more precise corrections on approach. So the main difference is that VASI offers glide-path guidance with a simpler, older two-bar design, while PAPI delivers more precise guidance with a four-light, higher-resolution system.