Fuel Jettison, more commonly referred to as Fuel Dumping, is the intentional, controlled, jettison of fuel from an aircraft whilst in flight.
Requirement
Most transport category aircraft have a maximum allowable takeoff weight that is in excess of the corresponding maximum landing weight. If the aircraft does not meet the regulatory engine out climb requirements at maximum takeoff weight or if the manufacturer has not made provisions to structurally allow for an "over-weight" landing capability , the aircraft will normally be equipped with a Fuel Dumping system.