FAA Ground School Practice Test

Which of the following indicates that a pilot is slightly low on the glide slope?

1. All white lights

2. One red light and three white lights

3. Pulsating green light

4. Steady red lights

The correct answer is: One red light and three white lights

When a pilot is slightly low on the glide slope while approaching for a landing, the Visual Glide Slope Indicator (VGSI) provides information through a series of colored lights. The presence of one red light and three white lights indicates that the aircraft is below the ideal glide slope path. The visual system used, such as the Precision Approach Path Indicator (PAPI) or the Visual Approach Slope Indicator (VASI), typically consists of multiple lights arranged in a series. When the lights display a mixture of red and white, it indicates the aircraft's position relative to the glide slope. In this case, seeing three white lights alongside one red light suggests that the aircraft is not positioned correctly for the ideal approach, specifically indicating that it is slightly low on the glide slope. Understanding the light signals helps pilots make necessary adjustments to their altitude and descent rate to ensure a proper approach and landing. The other scenarios presented do not indicate being slightly low on the glide slope as effectively as this combination of lights.