What is the minimum ceiling requirement at a destination airport, within 1 hour before or after ETA, if filing an alternate?

The correct answer is based on FAA regulations for operating under Part 135, which govern charter and commercial operations. When filing an alternate airport for a flight, the minimum ceiling requirement is set to ensure that pilots have a safe environment to execute procedures if the destination becomes unapproachable.

The requirement of a minimum ceiling of 1500 feet AGL plus the lowest circling minimums is pertinent because it provides an adequate margin of safety for visual reference when executing a circling approach, which often involves maneuvering the aircraft for landing. This helps to mitigate risk by ensuring that a pilot has a reasonable amount of vertical separation between the aircraft and potential obstacles in the vicinity of the airport.

While other answers propose varying ceiling requirements, they do not align with the stipulated regulations for alternate airport filing in Part 135 operations. Thus, the 1500 AGL plus circling minimums is the correct benchmark for ensuring safety and regulatory compliance in alternate airport scenarios.