What airborne incident requires immediate notification to the nearest NTSB field office?

Immediate notification to the nearest NTSB field office is required in the case of a flight control system malfunction or failure. This is because such malfunctions can pose serious safety risks, impacting the ability to control the aircraft and potentially leading to accidents or emergencies. The NTSB (National Transportation Safety Board) is responsible for investigating significant aviation accidents and incidents, and a flight control failure directly relates to flight safety. Timely reporting allows for a thorough investigation to determine causes, which can help improve safety measures in the aviation industry.

In contrast, incidents like engine noise during ascent, routine adjustments of cabin pressure, and weather-related turbulence generally do not require immediate notification as they are considered to be part of normal operational variances and do not directly threaten the aircraft's structural integrity or safety. Routine adjustments and minor noise issues can often be managed without escalating to the NTSB, as they do not typically indicate underlying technical failures that would warrant an investigation.