What is a requirement for aircraft operating under 14 CFR Part 135?

Aircraft operating under 14 CFR Part 135 are specifically designed for commuter and on-demand operations, including air taxi services. This regulatory part addresses the operational standards for aircraft that do not fall under the larger and more stringent regulations of Part 121, which apply to scheduled air carriers. By focusing on air taxi and certain commuter operations, Part 135 provides a framework that accommodates smaller aircraft and less frequent flights, making it suitable for business and leisure travel in a more versatile and immediate manner. This reflects the diversity of operations and allows for flexibility in the aviation industry.

The other choices do not accurately characterize the requirements of Part 135. For instance, a seating capacity of 20 or more is not mandatory for Part 135 operations, as many Part 135 aircraft can have fewer seats. Compliance with Part 121 standards is relevant to larger commercial operations, which is outside the scope of Part 135. Additionally, while payload limitations are significant for operational safety, the key factor for Part 135 is its emphasis on the type of operation (i.e., air taxi and commuter) rather than restricting aircraft to a specific maximum payload.