1 - During the time 1 hour before to 1 hour after the estimated arrival time
2 - Ceiling less than 2,000 feet
3 - Visibility less than 3 miles
If the above conditions exist, an alternate airport must be filed.
The alternate airport also has requirements that it must meet.
- If the airport has an instrument approach published, the weather must be forecast to be (at the ETA) better than the alternate airport minima specified in that approach or the following standard conditions:
- Precision Approach: 600ft ceiling and 2SM visibility
- Non-Precision Approach: 800ft ceiling and 2SM visibility