Circle-to-land is a maneuver initiated by the pilot to align the aircraft with a runway when a standard straight-in landing from an instrument approach is not possible or desirable. Circle-to-land maneuvers must only be executed after ATC authorization has been obtained and the pilot has established the required visual reference to the airport. Note that the visual reference must be established and maintained.
A circle-to-land maneuver is an alternative to a straight-in landing, used when a runway is not aligned within 30 degrees of the final approach course of the instrument approach procedure or the final approach requires 400 feet (or more) of descent per nautical mile.
When circling, the pilot must maintain a low altitude and speed while maneuvering in a confined airspace. The margin for error is slight, often calling for more advanced pilots.
Here are common methods used for circling. These are not exact maneuvers; As long as the aircraft is kept within the protected airspace, terrain and obstacle clearance is assured.