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The Pilots Desk
US-FAA14 CFR 121.617

Alternate airport for departure

Read the official rule

This regulation requires Part 121 air carriers to designate a departure alternate airport when weather at the departure airport is below landing minimums specified in their operations specifications.

When a departure alternate is required:

If takeoff weather is below the carrier's authorized landing minimums for that airport, dispatch must specify an alternate airport within:

  • Two-engine aircraft: 1 hour flying time at normal cruise speed with one engine inoperative
  • Three or more engines: 2 hours flying time at normal cruise speed with one engine inoperative

The departure alternate provides a nearby suitable airport if the aircraft must return shortly after takeoff due to mechanical issues or other emergencies when conditions at the departure airport are too poor for landing. The alternate's weather must meet the carrier's operations specifications requirements, and all required alternates must be listed in the dispatch release.

*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.*

This is an original plain-English explanation for training and reference, not legal advice and not for navigation. Always rely on the current official rule linked above. Last reviewed June 20, 2026.