What type of aircraft operations does FAR Part 121 cover?

FAR Part 121 specifically addresses the regulations surrounding scheduled air carrier operations, including those conducted by airlines that provide commercial passenger and cargo service. This part outlines the requirements for both the operators and the aircraft involved in these operations, ensuring a standard for safety, maintenance, and operational procedures.

The reason this is the correct choice is because Part 121 is integral to the regulatory framework that governs how airlines operate, including the necessity for those carriers to adhere to strict safety standards, training requirements for pilots and crew, and maintenance protocols for aircraft. These regulations are designed to protect the safety of passengers and crew members during commercial flight operations.

Other options refer to different types of operations that fall under different regulatory categories. For instance, military operations are governed under separate regulations that pertain to the specific needs and capabilities of military aircraft. Air ambulance services, while they may operate under Part 135 regulations in some cases, typically do not fall under the parameters defined by Part 121. Lastly, experimental flight operations are managed under Part 91 and require compliance with significantly different standards tailored for testing new aviation technology or aircraft configurations.