What indicates that a compressor stall has developed and stabilized during flight?

A compressor stall is a disturbance in the airflow within the compressor section of a gas turbine engine, and it can lead to various indications during flight. The key characteristic of a stabilized compressor stall is the presence of strong vibrations and a significant roar from the engine. This is due to the disruption in airflow and the subsequent unsteady operating conditions, which can produce a loud noise as air rapidly changes direction and pressure within the engine.

In this scenario, the strong vibrations are a physical manifestation of the stall, as mechanical components may be struggling to cope with altered airflow. The loud roar is often caused by turbulence and pressure fluctuations resulting from the stall conditions, indicating that the engine is not functioning within its normal operational parameters.

Other options point to different scenarios. An occasional loud bang with flow reversal is more of a transient occurrence rather than a stabilization, and a complete loss of power would imply that the engine is no longer operational, which is not necessarily characteristic of a stabilized stall. Dropping engine temperature without power loss could indicate other issues but does not specifically correlate with the stabilization of a compressor stall. Therefore, the presence of strong vibrations and a loud roar is the critical indicator of a compressor stall that has both developed and stabilized during flight.