Control-line flying is generally quite safe when all prescribed safety measures are followed. The airplane is constrained to fly in a circle, which is generally marked. A pilots' circle is also provided, so as long as the pilot stays in the pilot's circle and everyone else is outside the outer circle, the flying model can hit no one. In most competition categories, a "safety thong" connecting the control handle to the pilot's wrist is also required, so if the pilot inadvertently releases the handle, the airplane cannot fly outside the circle (and, frequently crashes, safely for others if not the airplane, when control is lost). The lines, handle, and control system are subjected to a "pull test" before flight to ensure that they are in good shape with some significant margin. For example, the pull test is around for a Stunt model (a 10G load), and the in-flight pull is around . This provides a 2x margin of safety even if one line should fail. One failed line immediately moves the elevator to the extreme of its movement, which almost always results in a crash, safely in the circle. Other categories of model are tested in a similar way, with the loads set to correspond to the expected speeds with a safety margin around a factor of 4.