Which one of these engines requires a functional check before installation?

The PT6A-65B engine, as indicated, requires a functional check before installation due to specific operational requirements and safety protocols associated with this engine model. The functional check is essential to ensure that all systems are operating correctly, including the fuel system, ignition system, and accessory components. Conducting a functional check helps in identifying potential issues that may not be apparent during a visual inspection alone.

Engines like the PT6A-20 and PT6A-52 may have different operational procedures or may not necessitate a functional check before installation to the same extent. Each model has its own maintenance guidelines, which dictate the need for functional checks based on design and operational complexities. The focus on the PT6A-65B highlights the importance of maintaining rigorous safety checks to prevent issues that could lead to engine malfunctions during operation.