What type of incident necessitates immediate notification to the nearest NTSB field office?

An in-flight fire is a serious emergency that poses immediate danger to the safety of the aircraft and its occupants. Such an incident can quickly escalate, impacting the aircraft's structural integrity and potentially leading to a catastrophic failure if not managed properly. The necessity for immediate notification to the NTSB's field office stems from the critical nature of the situation, which requires swift investigation and response to determine the cause of the fire and prevent future occurrences.

While other incidents such as a ground fire during preparation for takeoff, flight control system issues, and landing gear damage can also pose significant safety concerns, they typically do not hold the same level of urgency as an in-flight fire. In-flight fires can lead to more immediate and severe outcomes, necessitating a higher priority for investigation and documentation by the NTSB to enhance aviation safety protocols.