What action occurs when the landing gear free fall system is engaged?

When the landing gear free fall system is engaged, the primary action that occurs is that the landing gear descends by gravity. This system is designed as a backup mechanism for scenarios where hydraulic pressure is lost and the landing gear cannot be extended using the normal hydraulic system. In such situations, engaging the free fall system allows the gear to drop down due to its own weight, ensuring that the aircraft can land safely, even in the event of hydraulic failure.

Other options do not correctly describe the action of the free fall system. The gear cannot be locked in place by this system, as it is meant to facilitate extension rather than securing it. The gear does not extend using hydraulic force in free fall mode since that is precisely what would be avoided if hydraulic failure has occurred. Lastly, the gear does not retract immediately in this process; rather, the free fall system's sole purpose is to allow for the extension of the gear when necessary.