What causes an engine surge?

An engine surge occurs when there is a disruption in the airflow through the engine's compressor, leading to a stall of all or some of the compressor stages. This situation can arise when the balance between airflow and fuel flow is disrupted. In the scenario described by the choice deemed correct, all compressor stages have stalled. This means that the compressor blades can no longer effectively move air through the engine, which can be exacerbated by excessive fuel flow, creating an imbalance.

When excessive fuel flows into the engine without sufficient air to mix with, it can overwhelm the engine’s ability to maintain stable combustion. This can lead to pressure fluctuations and a critical point where the airflow collapses entirely, triggering a surge. In this case, all compressor stages stalling indicates a complete inability to manage the airflow properly, which solidifies the reasoning behind why this choice accurately describes a condition that leads to an engine surge.

The other options do not encompass the full mechanism behind engine surges in the same way. For instance, stalled compressor stages and low fuel flow might describe a different condition that does not align directly with the phenomenon of surge.