Which of the following is NOT typically required under Part 135 regulations?

The requirement for a flight instructor endorsement is not typically found within the regulatory framework of Part 135 operations. Part 135 is focused on the operation of smaller commercial aircraft, including commuter and on-demand services, emphasizing operating certificates, adherence to safety regulations, and special training and policies to ensure flight safety and operational integrity.

In the context of Part 135, an operating certificate is critical because it validates that the operator meets all required safety and operational standards set by the FAA. Compliance with safety regulations is a fundamental principle in aviation to protect passengers, crew, and the aircraft itself, making it an unavoidable requirement for all commercial operators. Special training and policies are also mandated under Part 135 to ensure that all personnel involved in flight operations are adequately prepared to manage varying flight conditions and emergencies.

While a flight instructor endorsement is important for individuals who are teaching flight maneuvers, it is not a prerequisite specifically tied to the operation of commercial flights under Part 135. Hence, it is the correct choice as the option that is not typically required in this regulatory context.