When Do You Need A Destination Alternate?

When dispatching or flying as IFR, it is important to check the weather at ETA at your destination airport in order to comply with regulations. 

First off, the destination airport need to comply with § 121.613 regardless if the operation is domestic, flag, or supplemental.

§ 121.613 states that: 

Except as provided in § 121.615, no person may dispatch or release an aircraft for operations under IFR or over-the-top, unless appropriate weather reports or forecasts, or any combination thereof, indicate that the weather conditions will be at or above the authorized minimums at the estimated time of arrival at the airport or airports to which dispatched or released.

The destination airport must be at or above visibility minimums, check out why authorized minimums is just visibility.

§ 121.619 - Domestic Operations IFR

Must follow the 1-2-3 rule, if ceiling or visibility are lower than the rule, you must list an alternate

• 1 hour before and after ETA of destination airport
  • 2000 ft ceiling
  • 3 statue mile visibility

§ 121.621 - Flag Operations IFR

All flag operations MUST list an alternate unless they meet these criteria:

• The flag operation flight is less than 6 hours
• 1 hour before and after ETA of destination airport
  • Must be above 1500 ft above the lowest circling MDA
  • or
  • 1500 ft above the lowest instrument approach landing minimum or 2000 ft above the airport elevation, whichever is higher
  • and
  • 3 statue mile visibility or 2 miles more than lowest visibility minimum found in the airport's IAP.

If no alternate can be found, such as a long oceanic crossing, you can add 2 or 3 hours (depending on your engine type) of fuel at cruising speed. (§ 121.641(b) or § 121.645(c))

§ 121.623 - Supplemental Operations IFR

All supplemental operations under IFR MUST list an alternate