Final answer:
A Tri-color VASI is an aviation instrument that helps pilots maintain the correct approach slope when landing an aircraft.
Step-by-step explanation:
A Tri-color VASI (Visual Approach Slope Indicator) is an aviation instrument that helps pilots maintain the correct approach slope when landing an aircraft. It consists of two sets of lights: white and red. The top row of lights is white, while the bottom row is red. When the pilot is at the correct approach slope, the pilot will see a combination of both white and red lights, creating a tri-color display. If the aircraft is too high, the pilot will see only white lights, and if the aircraft is too low, the pilot will see only red lights.