In the early days of the CM56 engines fitted to 737 Classics, double flame-outs occurred when the aircraft was descending at high airspeed at idle thrust and in very heavy rain. This was partially due to the airflow being compressed in the front part of the engine cowl and spilling over the edge while at the same time, rain being heavier formed the majority of air and water mixture entering the compressor. The fix was to increase the idle speed at closed throttle which in turn aided the airflow through the engine. Sorry if this is a pretty rough explanation.