How should you select an alternate when radiation or advection fog is forecast at the destination?

How should you select an alternate when radiation or advection fog is forecast at the destination?

• A. Ignore the forecast and proceed to destination
• B. Choose an alternate based solely on distance
• C. Check the forecast; if wind is not forecast more than 1 hour after ETA, use the alternate and hold until it clears
• D. Always fly to the planned destination despite fog forecasts

Answer: (C)

The key idea is that fog tends to lift when wind picks up, which mixes the air and dissipates the fog. When radiation or advection fog is forecast at the destination, you should plan based on whether the wind is expected to change within the first hour after your estimated arrival time. If the forecast shows no wind increase within that first hour, the fog is likely to persist, so you should choose an alternate and hold there until the fog clears. If wind is forecast to occur within that hour, the fog is likely to dissipate soon, so you can proceed toward the destination and land once conditions improve or hold at the destination until they do. This approach avoids proceeding into fog that may not lift quickly, while still allowing you the option to go if conditions are expected to improve promptly. The other options ignore forecast conditions, rely only on distance, or always go to the destination, which isn’t safe when fog is forecast.

The key idea is that fog tends to lift when wind picks up, which mixes the air and dissipates the fog. When radiation or advection fog is forecast at the destination, you should plan based on whether the wind is expected to change within the first hour after your estimated arrival time.

If the forecast shows no wind increase within that first hour, the fog is likely to persist, so you should choose an alternate and hold there until the fog clears. If wind is forecast to occur within that hour, the fog is likely to dissipate soon, so you can proceed toward the destination and land once conditions improve or hold at the destination until they do.

This approach avoids proceeding into fog that may not lift quickly, while still allowing you the option to go if conditions are expected to improve promptly. The other options ignore forecast conditions, rely only on distance, or always go to the destination, which isn’t safe when fog is forecast.