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Landing is the final phase in flight, in which the aircraft returns to the ground. The average vertical speed in a landing is around 2 meters per second; anything above is classed as "hard". Hard landings can be caused by weather conditions, mechanical problems, over-weight aircraft, pilot decision and/or pilot error. The term hard landing usually implies that the pilot still has total or partial control over the aircraft, as opposed to an uncontrolled descent into terrain (a crash). Hard landings can vary in their consequences, from mild passenger discomfort to vehicle damage, structural failure, injuries, and/or loss of life. When an aircraft has a hard landing, it must be inspected for damage before its next flight.
For helicopters, a hard landing can occur after mechanical or engine damage or failure when the rotor(s) are still intact and free to turn. Autorotation, in which airflow over the rotors keeps them turning and provides some lift, can allow limited pilot control during descent. As an unpowered descent, it requires considerable pilot skill and experience to safely execute.
A hard landing of a spacecraft such as a rocket stage usually ends with its destruction and can be intentional or unintentional. When a high-velocity impact is planned (when its purpose is to study consequences of impact), the spacecraft is called an impactor.