The SPECI visibility threshold is defined as the greatest of which values?

• A. The aerodrome's highest alternate minimum visibility or 5000m, whichever is greater
• B. Visibility above 10km
• C. The average visibility over the last hour
• D. The aerodrome altitude is rising

Answer: (A)

The key idea here is how the SPECI visibility threshold is determined. It uses two values and takes the larger one: the aerodrome’s highest alternate minimum visibility and 5000 meters. Whichever is greater becomes the threshold. This setup ensures a practical baseline of 5 kilometers, while also honoring any higher minimums that might be required for alternates.

For example, if the aerodrome’s highest alternate minimum visibility is 6,000 meters, the threshold is 6,000 meters. If that alternate minimum is 3,000 meters, the threshold remains 5,000 meters. The other options don’t fit because the threshold isn’t a fixed 10 kilometers, nor based on an hourly average, nor related to changes in altitude.