A compressor surge or compressor stall causes an abrupt reversal of airflow in the compressor. Compressor blades create a pumping action by working as airfoils. In a surge or stall, blades experience an aerodynamic stall (similar to an aircraft wing stalling) and become unable to hold back the higher pressure downstream, with a resulting violent flow reversal. The flame which is normally confined in the combustion chamber may come out of the engine inlet as well as the exhaust nozzle.