IFR: Alternate airport weather minimums

This regulation sets the weather standards required at an alternate airport when filing IFR flight plans under Part 135 operations.

For non-rotorcraft: You can only designate an alternate airport if weather reports or forecasts indicate conditions will meet or exceed the authorized alternate airport landing minimums at your estimated arrival time.

For rotorcraft: The weather at the alternate must meet specific minimums at your estimated arrival time:

• If an instrument approach exists for that airport, the ceiling must be at least 200 feet above the approach minimum, with visibility of at least 1 statute mile (but never less than the approach minimum visibility)
• If no instrument approach exists, conditions must allow descent from the minimum enroute altitude, approach, and landing under basic VFR

These requirements ensure your alternate airport will actually be usable if you need to divert from your destination. The Administrator may authorize exceptions to the rotorcraft requirements.

*This is a plain-English summary for study only. The official 14 CFR text on this page is controlling — always read the current regulation and consult a CFI.*