What is a primary hazard associated with volcanic ash ingestion?

Volcanic ash ingestion poses significant risks to aircraft engines, primarily leading to engine failure. When aircraft fly through volcanic ash clouds, the fine particles can enter the engines and cause various issues. The ash can erode engine components, obstruct air intakes, and disrupt combustion processes. These effects can lead to a loss of thrust and possibly total engine shutdown, which is a critical safety concern for aircraft operation.

In contrast, the other choices do not relate directly to the effects of volcanic ash. Increased fuel efficiency and improved engine performance are contrary to the actual outcomes resulting from volcanic ash ingestion, which tends to degrade engine performance and leads to increased fuel consumption and maintenance requirements. The option of "none of the above" fails to acknowledge the serious hazard that volcanic ash ingestion presents, making engine failure the only viable and accurate answer.