Flameout


In aviation, a flameout is the run-down of a jet engine due to the extinction of the flame in the combustion chamber. The loss of flame can have a variety of causes, such as fuel starvation, excessive altitude, compressor stall, foreign object damage deriving from birds, hail, or volcanic ash, severe precipitation, mechanical failure, or very cold ambient temperatures.

Engine control

Early jet engines were prone to flameout following disturbances of inlet airflow, or sudden or inappropriate thrust lever movements, which resulted in incorrect air-fuel ratios in the combustion chamber. Modern engines are much more robust in this respect, and are often digitally controlled, which allows for a significantly more effective control of all engine parameters to prevent flameouts and even initiate an automatic restart if a flameout occurs.
Flameouts occur most frequently at intermediate or low power settings such as in cruise and descent. To prevent a flameout when atmospheric or operational conditions are conducive to it, engine control systems usually provide a continuous ignition function. Ignitors are normally used only at engine start, until the flame in the combustion chamber becomes self-sustaining. With continuous ignition, instead, the ignitors are continuously sparked every second or less, so that if a flameout occurs, combustion can immediately be restored.

Engine restart

Following a flameout, jet engines can normally be restarted in flight, provided the aircraft is flying within the portion of its flight envelope defined as the engine relight envelope. Depending on where in the relight envelope the restart is attempted, the procedure may simply rely on the airflow or require the use of the starter in order for the compressor to achieve sufficient rotational speed for successful ignition.
For example, the Airbus A320 passenger jet has a maximum ceiling of over, but its certified engine relight envelope only extends to. Up to that altitude, a windmill restart can be attempted at airspeeds greater than ; below that speed, a starter-assisted relight is required.