Which situation requires notifying the nearest NTSB field office?

Notifying the nearest NTSB field office is required in situations where there is a significant safety concern that could affect future operations or safety standards. A flight control system failure falls into this category because it represents a critical failure that impacts the aircraft's controllability and safety during flight. Such failures can lead to serious incidents or accidents, and reporting them helps ensure that necessary investigations and preventive measures can be implemented.

In contrast, while engine failure during takeoff and reported hard landing damage can indeed be serious, they do not always require NTSB notification unless they result in injuries, fatalities, or substantial damage. Minor mechanical issues typically do not rise to the level of reporting, as they are usually manageable and do not pose an immediate threat to safety. This distinction highlights the importance of prioritizing notifications based on the severity and implications of the incidents.