What function does the landing gear free fall system serve?

The landing gear free fall system is designed to allow the landing gear to extend under the influence of gravity in the event that the normal hydraulic extension system fails. This feature is critical for ensuring that, even in a hydraulic failure scenario, the aircraft can safely land with the gear fully deployed. By relying on gravity, the free fall system provides a backup method for gear deployment that does not depend on the aircraft's hydraulic system. This redundancy is essential for enhancing the safety of the aircraft during critical phases of flight, particularly on approach and landing.

In contrast, the other functions described in the choices do not align with the purpose of the free fall system. For instance, manually retracting the landing gear would typically involve the pilot using the appropriate control switches in the cockpit, not a free fall mechanism. Providing backup hydraulic pressure is also not the role of the free fall system, as it is specifically designed to operate independently of the hydraulic system. Lastly, preventing accidental gear retraction pertains to safety mechanisms that ensure the gear remains locked during flight, which is unrelated to the free fall deployment technique.