When filing an IFR flight plan, the language of FAR 91.169 makes listing an alternate airport the default: You have to name one unless the circumstances of the flight are such that it falls under both of the two listed exceptions: First, the airport must have a published instrument approach procedure. Second, the forecast weather meets the 1-2-3 rule: For an hour before to an hour after the ETA at your destination, the weather is forecast to be equal to or better than a 2000-foot ceiling with three statute miles’ visibility.
