Which procedure should be followed regarding the hydraulic system before commencing towing operations?

The procedure that states the hydraulic system must be fully operational and connected before commencing towing operations is essential for ensuring the safety and effectiveness of the tow. A fully operational hydraulic system allows for critical functions such as braking and steering of the aircraft to remain under control during towing. This system is integral to managing the aircraft's weight and movement, and disconnecting or having it malfunction could lead to significant hazards, including loss of control or damage to either the aircraft or tow vehicle.

Having the hydraulic system operational ensures that all systems that rely on hydraulic power are functional, and any diagnostic checks can verify its readiness before any towing activities begin. This procedure is a standard safety protocol to prevent accidents and ensure a smooth towing process, making it crucial for the overall operation.