Describe the function of the vacuum system in multi-engine aircraft.

The vacuum system in multi-engine aircraft is primarily designed to operate gyroscopic instruments that require a vacuum source to function properly. These gyroscopic instruments, such as the artificial horizon (attitude indicator) and heading indicator, rely on a spinning gyroscope that maintains its orientation relative to the Earth's surface. To achieve this, a vacuum system generates negative pressure, which drives and stabilizes the gyroscope, allowing the instruments to provide accurate flight information.

The vacuum system is essential for the reliable operation of these instruments, especially in circumstances where electric systems may be less reliable due to failure or electrical interference. The use of a vacuum system adds redundancy to the aircraft's instrumentation, enhancing safety and operational integrity.

In contrast, other options such as powering the autopilot system, maintaining cabin pressure, or optimizing engine performance do not directly pertain to the vacuum system's primary role in the operation of essential flight instruments. Each of these functions is typically handled by different systems within the aircraft, underscoring the specialized use of the vacuum system in supporting gyroscopic instruments.