The center of light lenses is located how many inches from the PAPI base?

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Multiple Choice

The center of light lenses is located how many inches from the PAPI base?

The most important idea here is that the PAPI unit is built with a fixed mounting datum for its optical center. The center of the light lenses is set at a precise height above the base so that all the individual beams combine to create the correct glide path cue for pilots. For this particular PAPI setup, that fixed height is nine inches from the base. Maintaining that height ensures the optical axis aligns with the intended glide slope—so pilots see the correct angle on final approach. If the center were higher or lower than that specified height, the perceived glide path would shift, making the cue too steep or too shallow for safe landings.

The most important idea here is that the PAPI unit is built with a fixed mounting datum for its optical center. The center of the light lenses is set at a precise height above the base so that all the individual beams combine to create the correct glide path cue for pilots. For this particular PAPI setup, that fixed height is nine inches from the base. Maintaining that height ensures the optical axis aligns with the intended glide slope—so pilots see the correct angle on final approach. If the center were higher or lower than that specified height, the perceived glide path would shift, making the cue too steep or too shallow for safe landings.

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