REIL and its purpose?

• A. Runway Edge Lights; outline runway boundaries.
• B. Approach Lighting System; assist in visual acquisition.
• C. Runway End Identifier Lights; help identify the runway threshold.
• D. Marker Beacon; marks distance along approach.

Answer: (C)

REIL are two synchronized flashing lights placed at the runway threshold to give rapid, positive identification of the runway’s end. Their main job is to help pilots confirm exactly where the runway begins during the final approach, especially in low visibility or at night, so they can align with the landing zone without confusion. The lights flash together on opposite sides of the threshold, making the threshold unmistakable from a distance. This function is distinct from other lighting systems: Runway Edge Lights outline the sides of the runway, an Approach Lighting System assists visual acquisition along the approach path, and Marker Beacons indicate distances along the approach.