What requirement directs task certified control tower personnel to make tower prevailing visibility observations when the prevailing visibility at the usual observation point or at the tower level is less than 4 statute miles?

• A. ATC directives
• B. Observing Aids for Visibility
• C. Basic Weather Watch
• D. Cooperative Weather Watch

Answer: (A)

When visibility falls below four statute miles, the instruction comes from ATC directives, which require task certified control tower personnel to perform and report tower prevailing visibility observations. This ensures the weather data used for air traffic control and pilot decision-making reflects conditions right at the tower and near the airfield, where local factors can make actual visibility different from a more distant observation point. The other options describe tools or programs related to observing visibility or broader weather watch responsibilities, but they do not establish the specific requirement to measure and report tower prevailing visibility at low visibility thresholds.