What type of aircraft does CS 23 apply to?

The correct choice refers to aircraft that are classified as having 9 passenger seats or fewer and a Maximum Takeoff Weight (MTOW) greater than 5700 kg. CS 23, which stands for Certification Specification 23, outlines the airworthiness requirements for small aircraft, particularly those that fall below the higher safety and operational standards applicable to larger commercial aircraft.

This specification is designed to address the needs of general aviation aircraft, ensuring they meet safety standards while being adaptable for a range of small aircraft types, including those that may carry a limited number of passengers. The focus on a maximum seating capacity and a specific MTOW reflects the classification's intent to promote safety and operational reliability without imposing excessively stringent requirements that would be suitable for larger, more complex aircraft.

In contrast, the other options do not align with the scope of CS 23. For instance, commercial airliners with more than 100 seats and commuter aircraft with over 19 passenger seats are governed by different certification requirements due to their larger capacities and more complex operational demands. Motor gliders, while they have specific criteria for certification, do not fall under the convention of CS 23, which is strictly aimed at small general aviation aircraft.