1. Visual approach slope indicators (VASI) are a system of lights to provide visual descent information during an approach to landing.

2. The standard VASI consists of a two-barred tier of lights. You are
a. Below the glide path if both light bars are red; i.e., “red means dead.”
b. On the glide path if the far (on top visually) lights are red and the near (on bottom visually) lights are white.
c. Above the glide path if both light bars are white.

3. Remember, red over white (i.e., R before W alphabetically) is the desired sequence.
a. White over red is impossible.

4. VASI only projects a glide path. It has no bearing on runway alignment.

5. On a precision approach path indicator (PAPI),
a. Low is four red lights (less than 2.5°).
b. Slightly low is one white and three reds (2.8°).
c. On glide path is two whites and two reds (3.0°).
d. Slightly high is three whites and one red (3.2°).
e. High is four whites (more than 3.5°).

6. On a pulsating approach slope indicator (a VASI with flashing/pulsating signals),
a. Low is a pulsating red.
b. On glide path is a steady white or alternating red/white (depending on model).
c. High is a pulsating white.

7. Each pilot of an airplane approaching to land on a runway served by a visual approach slope indicator shall maintain an altitude at or above the glide slope until a lower altitude is necessary for landing (14 CFR 91.129).