When is a pilot allowed to fly without an alternate airport?

A pilot is allowed to fly without an alternate airport when the destination airport has an Instrument Approach Procedure (IAP) and meets the requirements of the "1-2-3 rule." This rule states that if the weather conditions at the destination airport are forecasted to be at or above certain minimums—specifically, if the destination is within one hour of the estimated time of arrival, the forecast visibility is at least 2 statute miles, and the ceiling is at least 1,000 feet above the airport elevation—then an alternate is not required. This rule is part of the FAA regulations that help ensure that pilots can safely plan their routes based on current and predicted weather conditions.

The other options do not provide a valid basis for bypassing the alternate airport requirement. Simply having clear weather on arrival does not guarantee that the flight can be conducted safely without an alternate, nor does it align with established regulations. Additionally, ATC instructions regarding filing alternates are not a standard rule and typically do not change the FAA's requirement for an alternate airport based on weather. Finally, flying under VFR conditions does not apply, as it pertains to visual flight rules where alternate requirements are still dictated by the regulations applicable to instrument flight plans.