What is a flameout and how does it occur?
Flameout basically means that the flame in the combustion chamber has been extinguished. A jet engine compresses air, then adds fuel and ignites it. So, it needs three things to function correctly- fuel, air (oxygen), and the heat to make them burn. Removing any of the three can cause a flameout.

It can happen for a number of reasons:


fuel starvation- Air Canada Flight 143 suffered flameout (due to wrong amount of fuel being put) and had to be landed like a glider.
Compressor stall (or surge)- The disruption of airflow due to compressor stall can cause an engine flameout.
Ingestion of foreign objects - British Airways Flight 9 suffered flameouts in all four engines due to ingestion of volcanic ash
Firing of armament- Early in its service A-10 Warthog suffered flameouts due to the engines ingesting the gassed generated while firing the GAU-8 Avenger.


Early jet engines (like the Jumo 004B) had high rates of flameout; however, modern jet engine flame outs are very rare, at the rate of about one every 100,000 non military flights. In most cases of flameout, the engines are restarted for resumption of flight.



Airspace magazine mentions a case where flameout happened because a F-100 ingested fuel (during aerial refueling); however, such occurrences are quite rare.