What type of lighting does a "VASI" provide?

The term "VASI" stands for Visual Approach Slope Indicator, which is a lighting system used at airports to aid pilots in visually determining whether they are on the correct approach path for landing. The VASI provides visual cues in the form of lights that indicate to the pilot whether they are on the proper glide slope. Specifically, the system typically consists of a row of lights that change color based on the aircraft's altitude relative to the ideal glide slope.

When pilots observe a series of white lights, it indicates that they are above the ideal approach path. Conversely, a combination of red and white lights suggests that they are on the correct slope, whereas all red lights signal that the aircraft is below the desired glide slope. This system is crucial for ensuring a safe and accurate approach, especially under visual flight conditions.

The other options do not relate to lighting systems used for approach guidance and are therefore not correct. Vertical Airspeed Indicator refers to an instrument used in the cockpit for measuring vertical speed; Visual Altitude Safety Indicator and Variable Area Slant Indicator are not recognized terms within aviation contexts regarding approach aids.