What action must a pilot take if deviating from any rule in Part 91 during an emergency?

In an emergency situation, a pilot is allowed to deviate from any rule in Part 91 to the extent necessary to deal with that emergency. The key requirement is that the pilot must notify Air Traffic Control (ATC) of the deviation when requested or follow up with a written report if it's deemed necessary. The purpose of this requirement is to ensure that safety protocols are maintained while also allowing flexibility to adjust procedures in urgent situations.

The necessity for documentation comes after the emergency has been resolved, as it aids regulatory bodies in understanding the circumstances that led to the deviation. This documentation provides insight into the decision-making process and any factors that influenced the pilot's actions during the emergency, which can be valuable for both oversight and for improving safety measures in the future.

While immediate notification to ATC in real-time is important, the requirement to send a written report upon request provides a structured way to account for the actions taken and the rationale behind them. Therefore, the necessity of the written report is foundational in maintaining a clear record and ensuring accountability within the operational framework established by the FAA.