Aerodrome facilities, including mechanical and electro-optical devices, providing vertical visual approach slope guidance to aircraft during the approach to landing. Lighting facilities provide this guidance by radiating a directional pattern of high-intensity red and white focused light beams that indicate to the pilot that he or she is "on slope," "above slope" or "below slope," depending on the combinations of lights that are showing. These lights are visible from at least 4 NM away (2.5 NM away for abbreviated installations). Visual approach slope indicator systems provide safe wheel clearance over the runway threshold and are related to the eye-to-wheel height (EWH) of the aircraft that the aerodrome is intended to serve.