A flameout refers to the failure of a jet engine caused by the extinction of the flame in the combustion chamber. It can be caused by a number of factors, including fuel exhaustion; compressor stall; insufficient oxygen supply; foreign object damage such as birds, hail or even volcanic ash; severe weather conditions; and mechanical failure. Flameouts occur most frequently when the engine is at an intermediate or low power setting (such as during the cruise and descent phases of flight. Most of the time, they are recovered from uneventfully. To recover from a flameout, the pilot should ensure the engine's fuel supply has been restored and then simply perform an engine restart as detailed in the aircraft's Flight Operations Manual. Early jet engines were at relatively high risk of flameout. Fast acceleration or inappropriate throttle settings could impoverish the fuel/air mixture causing a flameout. If this happened at low altitude, it would often lead to the total loss of the aircraft. However, modern jets are engineered to a higher degree of technical quality and are controlled by systems that constantly fine-tune their performance; as such flameouts are not such a risk as they were in the early days of jet-powered aviation.