badge has achieved an altitude gain of , made a flight of five-hours duration, and flown cross-country for a straight-line distance of at least . A pilot who has completed the three parts of the Diamond Badge has flown to a pre-defined goal, has flown in one flight (but not necessarily to a pre-defined goal) and gained in height. The FAI also issues a diploma for a flight of and further diplomas for increments of . Landing out If lift is not found during a cross-country flight, for example because of deteriorating weather, the pilot must choose a location to "land out". Although inconvenient and often mistaken for "emergency landings", landing out (or "outlanding") is a routine event in cross-country gliding. A location needs to be identified where the glider can land safely without damaging the glider, the pilot, or property such as crops or livestock. The glider and the pilot(s) can then be retrieved by road from the outlanding location using a purpose-built trailer. If this is not possible due to an inaccessible location such as a mountain range, the glider may be loaded into its trailer and airlifted by helicopter. In some instances, a tow-plane can be summoned to re-launch the aircraft. Use of engines or motors Although adding to the weight and expense, some gliders are fitted with small power units and are known as motor gliders. This avoids the inconvenience of landing out. The power units can be internal combustion engines, electrical motors, or retractable jet engines. Retractable propellers are fitted to high performance sailplanes, though in another category, called touring motor gliders, non-retractable propellers are used. Some powered gliders are "self launching", which makes the glider independent of a tow plane. However some gliders have "sustainer" engines that can prolong flight but are not powerful enough for launching. All power units have to be started at a height that includes a margin that would still allow a safe landing out to be made, if there were a failure to start. In a competition, using the engine ends the soaring flight. Unpowered gliders are lighter and, as they do not need a safety margin for starting the engine, they can safely thermal at lower altitudes in weaker conditions. Consequently, pilots in unpowered gliders may complete competition flights when some powered competitors cannot. Conversely, motor glider pilots can start the engine if conditions will no longer support