Under what circumstance might an aircraft's engine logbook be empty of previous operating history?

The correct answer is that after an engine rebuilding by the manufacturer, the engine logbook may be empty of previous operating history. When an engine is rebuilt, especially if it is done by the manufacturer or a certified facility, it is typically considered a new engine in terms of operational history. As part of this process, the previous log entries may be reset or rendered irrelevant, and a new logbook may be initiated to reflect the engine’s current status, any modifications made during the rebuilding process, and its new flight history.

This situation can arise because the rebuilding process could involve substantial changes to engine internals or configurations, effectively giving it a new operational life. Consequently, there would not be any operational history to document in the logbook until the engine begins new flights and accumulates flight hours again.

While other scenarios may lead to an empty logbook, such as a new registration or an aircraft's first flight, these do not specifically relate to the operational history of the engine itself, which is why they do not serve as the best choices in this context. Regular maintenance checks should not result in an empty logbook either; rather, they would typically add to the existing operational history.