When portions of the horizon are obstructed by buildings or aircraft, which value should be used as a guide to determine surface visibility?

• A. Surface prevailing visibility
• B. Tower visibility
• C. PIREPs
• D. Control tower values of prevailing visibility

Answer: (D)

When the horizon is blocked by buildings or other aircraft, you can’t rely on a ground-level or horizon-based sighting to judge surface visibility. The appropriate guide is the prevailing visibility reported by the control tower. The tower’s vantage point over the field provides a field-wide, standardized value that aircraft operations use for surface visibility in obstructed conditions. Pilots’ PIREPs are useful for broader weather context but aren’t the authoritative reference for surface visibility at the airport; they’re individual observations, not the field-wide measure. A tower-based prevailing visibility value therefore gives the most consistent and applicable reference under obstruction.