Under what circumstances should the nearest NTSB field office be notified immediately?

The situation in which the nearest NTSB field office should be notified immediately is an in-flight fire. This is because an in-flight fire poses a significant threat to the safety of the aircraft, passengers, and crew. It can lead to critical emergencies that require immediate response and investigation to ensure safety protocols are followed and to understand the circumstances that led to the incident.

Notifying the NTSB about an in-flight fire is essential, as it prompts an investigation into the cause of the fire, assessing whether it was due to mechanical failure, human error, or other factors. This is part of the NTSB's role in ensuring aviation safety by gathering data and making recommendations to prevent similar occurrences in the future.

Other situations, such as in-flight turbulence causing passenger discomfort, routine maintenance, or a scheduled landing approach, do not warrant immediate notification to the NTSB. While these events may require reporting under different circumstances or might be addressed in operational procedures, they do not involve the immediate risks to safety that an in-flight fire entails.