What happens if the main hydraulic system fails?

When the main hydraulic system fails, the emergency hydraulic system is designed to activate as a backup. This feature is critical for maintaining control of the aircraft's essential flight operations. The emergency system typically powers key components that are necessary for safety, allowing the pilots to retain control and manage the situation effectively.

The presence of an emergency hydraulic system helps ensure that essential functions, such as control surfaces and landing gear, remain operable, thus preventing a catastrophic scenario.

The other options imply more severe consequences that are not necessarily true. Shutting down the aircraft is not a typical response to a hydraulic failure, as there are always safety procedures in place to handle such failures. Only the lights failing suggests a very limited scope of failure unrelated to the hydraulic system's function, and claiming that the aircraft would be unable to fly ignores the role of redundancy and backup systems that allow for continued operation.