Which of the following is NOT a requirement for a safety pilot?

The requirement for a safety pilot does not include holding a flight instructor rating. A safety pilot's primary role is to assist the pilot flying under visual flight rules (VFR) when they are operating in conditions that may not allow them to maintain visual reference to the ground. To perform this role, a safety pilot is required to hold a valid medical certificate, possess at least a private pilot license, and have the appropriate category and class rating for the aircraft being flown. These qualifications ensure that the safety pilot has the necessary skills and authority to operate the aircraft and be responsible for the flight safety, but there is no requirement for them to have a flight instructor rating.

While a flight instructor rating may indicate a higher level of training and experience, it is not essential for the function of a safety pilot in VFR flight. Therefore, the requirement to be a certified flight instructor is not relevant in this context, making it the correct answer to the question.