What is a key safety feature of the main gear manual extension system?

The key safety feature of the main gear manual extension system is that it allows manual control transfer to the emergency system. This capability is crucial because in the event of a failure in the primary landing gear system, crew members can manually operate the gear extension. This system provides an alternative means to lower the landing gear, safeguarding against complete loss of function. It enhances the aircraft's safety by ensuring that pilots still have a method to deploy the landing gear and land safely, thus preventing potential accidents.

In contrast to this answer, the options involving automatic functions, mechanical unlocking, or visual inspection points do not describe the primary purpose of the manual extension system. Rather than allowing for automatic retraction, the system is specifically designed for situations where pilots need to take over control in an emergency. It does not deal with the unlocking of the nose gear provided by a different mechanism, and while visual inspection is important for overall maintenance, it is not a direct safety feature of the extension system itself.