Which description matches a device that looks like four telescopes looking at each other?

• A. Localizer
• B. PAPI
• C. Transmissometer
• D. Glide Path

Answer: (C)

The device described is used to measure visibility along the approach by sending a beam of light from one end to the other and detecting how much light gets through. This arrangement—two optical ends facing each other, sometimes with multiple viewing apertures—fits the transmissometer, which provides Runway Visual Range data for controllers and pilots.

Localizer is an array of antennas that provides lateral guidance on the ILS, not a light-beam visibility sensor. PAPI is a row of lights on the approach end that visually indicate glide slope to the pilot. Glide path (glideslope) is the vertical guidance lighting system used with the ILS. So, the description of four telescopes facing each other points to the transmissometer, the instrument that measures visibility rather than directing or lighting the approach.