Describe the 1,2,3 rule for determining a destination alternate.

Describe the 1,2,3 rule for determining a destination alternate.

• A. If the forecast is worse than 1 hour before departure, an alternate is required
• B. If weather at or below 1 hour before and after is 2,000 ft ceiling and 3 SM visibility, a destination alternate is not required
• C. If weather is below minimums at destination, an alternate is required
• D. The rule applies only to domestic flights

Answer: (B)

The key idea is to decide if you must have a destination alternate based on the forecast for the time you plan to arrive. The 1-2-3 rule considers the window around the estimated time of arrival: one hour before to one hour after. If, within that window, the forecast weather at the destination is at least 2,000 feet in ceiling and 3 statute miles of visibility, you do not need a destination alternate. That’s why this option is best: it states that weather at or within one hour before and after the ETA being 2,000 ft ceiling and 3 SM visibility means an alternate is not required. If the forecast during that window is worse than those thresholds (lower ceiling or lower visibility), you would need to designate an alternate. The rule is about the ETA window, not departure time, and it applies to planning scenarios beyond just domestic flights.

The key idea is to decide if you must have a destination alternate based on the forecast for the time you plan to arrive. The 1-2-3 rule considers the window around the estimated time of arrival: one hour before to one hour after. If, within that window, the forecast weather at the destination is at least 2,000 feet in ceiling and 3 statute miles of visibility, you do not need a destination alternate. That’s why this option is best: it states that weather at or within one hour before and after the ETA being 2,000 ft ceiling and 3 SM visibility means an alternate is not required.

If the forecast during that window is worse than those thresholds (lower ceiling or lower visibility), you would need to designate an alternate. The rule is about the ETA window, not departure time, and it applies to planning scenarios beyond just domestic flights.