Within what time frame must the nearest NTSB field office be notified when an aircraft is involved in an accident resulting in substantial damage?

When an aircraft is involved in an accident that results in substantial damage, the appropriate protocol requires immediate notification to the nearest National Transportation Safety Board (NTSB) field office. This urgency is essential as it allows for a swift response, which can include an investigation to determine the cause of the accident, collection of evidence, and ensuring the safety of aviation operations.

Immediate notification serves several crucial functions: it helps facilitate timely investigations, protects the integrity of the accident site, and allows the NTSB to coordinate any necessary resources or assistance. This prompt response is vital in aviation safety measures, leading to better understanding and prevention of future incidents.

The other timeframes are not aligned with the NTSB's requirement for immediate reporting. While there are regulations for follow-up reports or notifications within specific periods, the initial report to the NTSB must happen right away to ensure all relevant actions can be taken without delay.